Internet Draft Electronic Signature Formats
Internet Draft ETSI TC-SEC (ETSI)
S/MIME Working Group D. Pinkas (Bull)
expires in six months J. Ross (Security & Standards)
Target Category: Informational N. Pope (Security & Standards)
March 2001
Electronic Signature Formats
for long term electronic signatures
<draft-ietf-smime-esformats-04.txt>
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Abstract
The informational RFC defines the format of an electronic signature
that can remain valid over long periods. This includes evidence as to
its validity even if the signer or verifying party later attempts to
deny (i.e. repudiates, see [ISONR]) the validity of the signature.
The format can be considered as an extension to RFC 2630 [CMS] and RFC
2634 [ESS], where, when appropriate additional signed and unsigned
attributes have been defined.
The contents of this Informational RFC is technically equivalent to
ETSI TS 101 733 V.1.2.2. The ETSI TS is under the ETSI Copyright (C).
Individual copies of this ETSI deliverable can be downloaded from
http://www.etsi.org
1. Introduction
This document is intended to cover electronic signatures for various
types of transactions, including business transactions (e.g. purchase
requisition, contract, and invoice applications) where long term
validity of such signatures is important.
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Electronic signatures can be used for any transaction between an
individual and a company, between two companies, between an individual
and a governmental body, etc. This document is independent of any
environment. It can be applied to any environment e.g. smart cards, GSM
SIM cards, special programs for electronic signatures etc.
An electronic signature produced in accordance with this document
provides evidence that can be processed to get confidence that some
commitment has been explicitly endorsed under a signature policy, at a
given time, by a signer under an identifier, e.g. a name or a
pseudonym, and optionally a role.
The European Directive on a community framework for Electronic
Signatures defines an electronic signature as: "data in electronic form
which is attached to or logically associated with other electronic data
and which serves as a method of authentication". An electronic
signature as used in the current document is a form of advanced
electronic signature as defined in the Directive.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in [RFC2119].
TABLE OF CONTENTS
1. Introduction 1
2 Overview 4
2.1 Aim 4
2.2 Basis of Present Document 4
2.3 Major Parties 5
2.4 Electronic Signatures and Validation Data 6
2.5 Forms of Validation Data 7
2.6 Extended Forms of Validation Data 10
2.7 Archive Validation Data 12
2.8 Arbitration 13
2.9 Validation Process 13
2.10 Example Validation Sequence 14
2.11 Additional optional features 19
3. Data structure of an Electronic Signature 20
3.1 General Syntax 20
3.2 Data Content Type 20
3.3 Signed-data Content Type 20
3.4 SignedData Type 20
3.5 EncapsulatedContentInfo Type 21
3.6 SignerInfo Type 21
3.6.1 Message Digest Calculation Process 21
3.6.2 Message Signature Generation Process 21
3.6.3 Message Signature Verification Process 21
3.7 CMS Imported Mandatory Present Attributes 22
3.7.1 Content Type 22
3.7.2 Message Digest 22
3.7.3 Signing Time 22
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3.8 Alternative Signing Certificate Attributes 22
3.8.1 ESS Signing Certificate Attribute Definition 22
3.8.2 Other Signing Certificate Attribute Definition 23
3.9 Additional Mandatory Attributes 24
3.9.1 Signature policy Identifier 24
3.10 CMS Imported Optional Attributes 26
3.10.1 Countersignature 26
3.11 ESS Imported Optional Attributes 26
3.11.1 Content Reference Attribute 27
3.11.2 Content Identifier Attribute 27
3.11.3 Content Hints Attribute 27
3.12 Additional Optional Attributes 28
3.12.1 Commitment Type Indication Attribute 28
3.12.2 Signer Location attribute 30
3.12.3 Signer Attributes attribute 31
3.12.4 Content Timestamp attribute 31
3.13 Support for Multiple Signatures 32
3.13.1 Independent Signatures 32
3.13.2 Embedded Signatures 32
4. Validation Data 32
4.1 Electronic Signature Timestamp 33
4.1.1 Signature Timestamp Attribute Definition 33
4.2 Complete Validation Data 34
4.2.1 Complete Certificate Refs Attribute Definition 35
4.2.2 Complete Revocation Refs Attribute Definition 35
4.3 Extended Validation Data 37
4.3.1 Certificate Values Attribute Definition 37
4.3.2 Revocation Values Attribute Definition 38
4.3.3 ES-C Timestamp Attribute Definition 38
4.3.4 Time-Stamped Certificates and CRLs Attribute Definition 39
4.4 Archive Validation Data 39
4.4.1 Archive Timestamp Attribute Definition 40
5. Security considerations 41
5.1 Protection of Private Key 41
5.2 Choice of Algorithms 41
6. Conformance Requirements 41
6.1 Signer 41
6.2 Verifier using timestamping 42
6.3 Verifier using secure records 42
7. References 43
8. Authors' Addresses 44
9. Full Copyright Statement 45
Annex A (normative): ASN.1 Definitions 46
A.1 Definitions Using X.208 (1988) ASN.1 Syntax 46
A.2 Definitions Using X.680 1997 ASN.1 Syntax 54
Annex B (informative): General Description 64
B.1 The Signature Policy 64
B.2 Signed Information 65
B.3 Components of an Electronic Signature 65
B.3.1 Reference to the Signature Policy 65
B.3.2 Commitment Type Indication 66
B.3.3 Certificate Identifier from the Signer 67
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B.3.4. Role Attributes 68
B.3.4.1 Claimed Role 68
B.3.4.2 Certified Role 68
B.3.5 Signer Location 69
B.3.6 Signing Time 69
B.3.7 Content Format 70
B.4 Components of Validation Data 70
B.4.1 Revocation Status Information 70
B.4.2 CRL Information 71
B.4.3 OCSP Information 72
B.4.4 Certification Path 72
B.4.5 Timestamping for Long Life of Signature 73
B.4.6 Timestamping before CA Key Compromises 74
B.4.6.1 Timestamping the ES with Complete validation data 75
B.4.6.2 Timestamping Certificates and Revocation Information 75
B.4.7 Timestamping for Long Life of Signature 76
B.4.8 Reference to Additional Data 77
B.4.9 Timestamping for Mutual Recognition 77
B.4.10 TSA Key Compromise 78
B.5 Multiple Signatures 79
Annex C (informative): Identifiers and roles 79
C.1 Signer Name Forms 79
C.2 TSP Name Forms 79
C.3 Roles and Signer Attributes 80
2 Overview
2.1 Aim
The aim of this document is to define an Electronic Signature (ES) that
remains valid over long periods. This includes evidence as to its
validity even if the signer or verifying party later attempts to deny
(repudiates) the validity of the signature.
This document specifies the use of trusted service providers (e.g.
TimeStamping Authorities (TSA)), and the data that needs to be archived
(e.g. cross certificates and revocation lists) to meet the requirements
of long term electronic signatures. An electronic signature defined by
this document can be used for arbitration in case of a dispute between
the signer and verifier, which may occur at some later time, even years
later. This document uses a signature policy, referenced by the signer,
as the basis for establishing the validity of an electronic signature.
2.2 Basis of Present Document
This document is based on the use of public key cryptography to produce
digital signatures, supported by public key certificates.
A Public key certificate is a public keys of a user, together with some
other information, rendered unforgeable by encipherment with the
private key of the Certification Authority (CA) which issued it (ITU-T
Recommendation X.509 [1]).
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This document also specifies the uses of timestamping services to prove
the validity of a signature long after the normal lifetime of critical
elements of an electronic signature and to support non-repudiation. It
also, as an option, defines the use of additional timestamps to provide
very long-term protection against key compromise or weakened
algorithms.
This document builds on existing standards that are widely adopted.
This includes:
* RFC 2459 [RFC2459] Internet X.509 Public Key Infrastructure
Certificate and CRL Profile (PKIX);
* RFC 2630 [CMS] Crytographic Message Syntax (CMS);
* RFC 2634 [ESS] Enhanced Security Services (ESS);
* RFC 2439 [OCSP] One-line Certificate Status Protocol (OCSP);
* ITU-T Recommendation X.509 [1] Authentication framework;
* RFC (to be published) [TSP] PKIX Time Stamping protocol (TSP).
NOTE: See section 7 for a full set of references.
2.3 Major Parties
The following are the major parties involved in a business transaction
supported by electronic signatures as defined in this document:
* the Signer;
* the Verifier;
* the Arbitrator;
* Trusted Service Providers (TSP).
A Signer is an entity that initially creates the electronic signature.
When the signer digitally signs over data using the prescribed format,
this represents a commitment on behalf of the signing entity to the
data being signed.
A verifier is an entity that verifies an evidence. (ISO/IEC 13888-1
[13]). Within the context of this document this is an entity that
validates an electronic signature.
An arbitrator, is an entity which arbitrates disputes between a signer
and a verifier when there is a disagreement on the validity of a
digital signature.
Trusted Service Providers (TSPs) are one or more entities that help
to build trust relationships between the signer and verifier. Use of
some specific TSP services MAY be mandated by signature policy. TSP
supporting services may provide the following information: user
certificates, cross-certificates, timestamping tokens, CRLs, ARLs,
OCSP responses.
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The following TSPs are used to support the validation or
the verification of electronic signatures :
* Certification Authorities;
* Registration Authorities;
* Repository Authorities (e.g. a Directory);
* TimeStamping Authorities;
* One-line Certificate Status Protocol responders;
* Attribute Authorities;
* Signature Policy Issuers.
Certification Authorities provide users with public key certificates.
Registration Authorities allows the registration of entities before a
CA generates certificates.
Repository Authorities publish CRLs issued by CAs, cross-certificates
(i.e. CA certificates) issued by CAs, signature policies issued by
Signature Policy Issuers and optionally public key certificates (i.e.
leaf certificates) issued by CAs.
TimeStamping Authorities attest that some data was formed before a
given trusted time.
One-line Certificate Status Protocol responders (OSCP responders)
provide information about the status (i.e. revoked, not revoked,
unknown) of a particular certificate.
A Signature Policy Issuer issues signatures policies that define the
technical and procedural requirements for electronic signature
creation, validation and verification, in order to meet a particular
business need.
Attributes Authorities provide users with attributes linked to public
key certificates
2.4 Electronic Signatures and Validation Data
Validation of an electronic signature in accordance with this document
requires:
* The electronic signature; this includes:
- the signature policy;
- the signed user data;
- the digital signature;
- other signed attributes provided by the signer;
. - other unsigned attributes provided by the signer.
* Validation data which is the additional data needed to validate
the electronic signature; this includes:
- certificates references;
- certificates;
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- revocation status information references;
- revocation status information;
- time-stamps from Time Stamping Authorities (TSAs).
* The signature policy specifies the technical requirements on
signature creation and validation in order to meet a particular
business need. A given legal/contractual context may recognize a
particular signature policy as meeting its requirements.
For example: a specific signature policy may be recognized by court
of law as meeting the requirements of the European Directive for
electronic commerce. A signature policy may be written using a formal
notation like ASN.1 or in an informal free text form provided the
rules of the policy are clearly identified. However, for a given
signature policy there shall be one definitive form which has a unique
binary encoded value.
Signed user data is the user's data that is signed.
The Digital Signature is the digital signature applied over the
following attributes provided by the signer:
* hash of the user data (message digest);
* signature Policy Identifier;
* other signed attributes
The other signed attributes include any additional information which
must be signed to conform to the signature policy or this document
(e.g. signing time).
According to the requirements of a specific signature policy in use,
various Validation Data shall be collected and attached to or
associated with the signature structure by the signer and/or the
verifier. The validation data includes CA certificates as well as
revocation status information in the form of certificate revocation
lists (CRLs) or certificate status information provided by an on-line
service. Additional data also includes timestamps and other time
related data used to provide evidence of the timing of given events. It
is required, as a minimum, that either the signer or verifier obtains a
timestamp over the signer's signature or a secure time record of the
electronic signature must be maintained. Such secure records must not
be undetectably modified and must record the time close to when the
signature was first validated.
2.5 Forms of Validation Data
An electronic signature may exist in many forms including:
* the Electronic Signature (ES), which includes the digital
signature and other basic information provided by the signer;
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* the ES with Timestamp (ES-T), which adds a timestamp to the
Electronic Signature, to take initial steps towards providing
long term validity;
* the ES with Complete validation data (ES-C), which adds to the
ES-T references to the complete set of data supporting the
validity of the electronic signature (i.e. revocation status
information).
The signer must provide at least the ES form, but in some cases may
decide to provide the ES-T form and in the extreme case could provide
the ES-C form. If the signer does not provide ES-T, the verifier must
either create the ES-T on first receipt of an electronic signature or
shall keep a secure time record of the ES. Either of these two
approaches provide independent evidence of the existence of
the signature at the time it was first verified which should be near
the time it was created, and so protects against later repudiation of
the existence of the signature. If the signer does not provide ES-C the
verifier must create the ES-C when the complete set of revocation and
other validation data is available.
The ES satisfies the legal requirements for electronic signatures as
defined in the European Directive on electronic signatures, see Annex C
for further discussion on relationship of this document to the
Directive. It provides basic authentication and integrity protection
and can be created without accessing on-line (timestamping) services.
However, without the addition of a timestamp or a secure time record
the electronic signature does not protect against the threat that the
signer later denies having created the electronic signature (i.e. does
not provide non-repudiation of its existence).
The ES-T time-stamp or time record should be created close to the time
that ES was created to provide protection against repudiation. At this
time all the data needed to complete the validation may not be
available but what information is readily available may be used to
carry out some of the initial checks. For example, only part of the
revocation information may be available for verification at that point
in time. Generally, the ES-C form cannot be created at the same time as
the ES, as it is necessary to allow time for any revocation information
to be captured. Also, if a certificate is found to be temporarily
suspended, it will be necessary to wait until the end of the suspension
period.
The signer should only create the ES-C in situations where it was
prepared to wait for a sufficient length of time after creating the ES
form before dispatching the ES-C. This, however, has the advantage that
the verifier can be presented with the complete set of data supporting
the validity of the ES.
Support for ES-C by the verifier is mandated (see section 6 for
specific conformance requirements).
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An Electronic Signature (ES), with the additional validation data
forming the ES-T and ES-C is illustrated in Figure 1:
+------------------------------------------------------------ES-C-----+
|+--------------------------------------------ES-T-----+ |
||+------Elect.Signature (ES)----------+ +------------+| +-----------+|
|||+---------+ +----------+ +---------+| |Timestamp || |Complete ||
||||Signature| | Other | | Digital || |over digital|| |certificate||
||||Policy ID| | Signed | |Signature|| |signature || |and ||
|||| | |Attributes| | || +------------+| |revocation ||
|||+---------+ +----------+ +---------+| | |references ||
||+------------------------------------+ | +-----------+|
|+-----------------------------------------------------+ |
+---------------------------------------------------------------------+
Figure 1: Illustration of an ES, ES-T and ES-C
The verifiers conformance requirements of an ES with a timestamp of the
digital signature is defined in subsection 6.2.
The ES on its own satisfies the legal requirements for electronic
signatures as defined in the European Directive on electronic
signatures. The signers conformance requirements of an ES are defined
in subsection 6.1, and are met using a structure as indicated in figure
2:
+------Elect.Signature (ES)-----------|
|+---------+ +----------+ +---------+ |
||Signature| | Other | | Digital | |
||Policy ID| | Signed | |Signature| |
|| | |Attributes| | | |
|+---------+ +----------+ +---------+ |
|+-----------------------------------+|
Figure 2: Illustration of an ES
Where there are requirements for long term signatures without
timestamping the digital signature, then a secure record is needed of
the time of verification in association with the electronic signature
(i.e. both must be securely recorded). In addition the certificates
and revocation information used at the time of verification should to
be recorded as indicated in figure 3 as an ES-C(bis).
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+-------------------------------------------------------ES-C-----+
| |
| +------Elect.Signature (ES)----------+| +-----------+|
| |+---------+ +----------+ +---------+|| |Complete ||
| ||Signature| | Other | | Digital ||| |certificate||
| ||Policy ID| | Signed | |Signature||| |and ||
| || | |Attributes| | ||| |revocation ||
| |+---------+ +----------+ +---------+|| |references ||
| +------------------------------------+| +-----------+|
| |
+----------------------------------------------------------------+
Figure 3: Illustration of an ES-C(bis)
The verifiers conformance requirements of an ES-C(bis) is defined in
subsection 6.3.
Note: A timestamp attached to the electronic signature or a secure time
record helps to protect the validity of the signature even if some of
the verification data associated with the signature become compromised
AFTER the signature was generated. The timestamp or a secure time
record provides evidence that the signature was generated BEFORE the
event of compromise; hence the signature will maintain its validity
status.
2.6 Extended Forms of Validation Data
The complete validation data (ES-C) described above may be extended to
form an ES with eXtended validation data (ES-X) to meet following
additional requirements.
Firstly, when the verifier does not has access to,
* the signer's certificate,
* all the CA certificates that make up the full certification
path,
* all the associated revocation status information, as referenced
in the ES-C.
then the values of these certificates and revocation information may be
added to the ES-C. This form of extended validation data is called a
X-Long.
Secondly, if there is a risk that any CA keys used in the certificate
chain may be compromised, then it is necessary to additionally
timestamp the validation data by either:
* timestamping all the validation data as held with the ES(ES-C),
this eXtended validation data is called a Type 1 X-Timestamp; or
* timestamping individual reference data as used for complete
validation.
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This form of eXtended validation data is called a Type 2 X-Timestamp.
NOTE: The advantages/drawbacks for Type 1 and Type 2 X-Timestamp are
discussed in this document (see section B.4.6.)
If all the above conditions occur then a combination of the two formats
above may be used. This form of eXtended validation data is called
a X-Long-Timestamped.
Support for the extended forms of validation data is optional.
An Electronic Signature (ES) , with the additional validation data
forming the ES-X long is illustrated in Figure 4:
+------------------------------------------------------- ES-X Long--+
|+--------------------------------------- EC-C --------+ |
||+---- Elect.Signature (ES)----+ +--------+| +--------+ |
|||+-------+-+-------+-+-------+| +---------+|Complete|| |Complete| |
||||Signa- | |Other | |Digital|| |Timestamp||certi- || |certi- | |
||||ture | |Signed | |Signa- || |over ||ficate || |ficate | |
||||Policy | |Attri- | |ture || |digital ||and || |and | |
||||ID | |butes | | || |signature||revoc. || |revoc. | |
|||+-------+ +-------+ +-------+| +---------+|refs || |data | |
||+-----------------------------+ +--------+| +--------+ |
|+-----------------------------------------------------+ |
+-------------------------------------------------------------------+
Figure 4: Illustration of an ES and ES-X long.
An Electronic Signature (ES) , with the additional validation data
forming the eXtended Validation Data - Type 1 is illustrated in
Figure 5:
+---------------------------------------------------------- ES-X 1 -+
|+---------------------------------------- EC-C --------+ |
|| +---- Elect.Signature (ES)----+ +--------+| +-------+ |
|| |+-------+ +-------+ +-------+| +---------+|Complete|| | | |
|| ||Signa- | |Other | |Digital|| |Timestamp||certifi-|| | Time- | |
|| ||ture | |Signed | |Signa- || |over ||cate and|| | stamp | |
|| ||Policy | |Attri- | |ture || |digital ||revoc. || | over | |
|| ||ID | |butes | | || |signature||refs || | CES | |
|| |+-------+ +-------+ +-------+| +---------+| || | | |
|| +-----------------------------+ +--------+| +-------+ |
|+------------------------------------------------------+ |
+-------------------------------------------------------------------+
Figure 5: Illustration of ES with ES-X Type 1
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An Electronic Signature (ES) , with the additional validation data
forming the eXtended Validation Data - Type 2 is illustrated in
Figure 6:
+-------------------------------------------------------- ES-X 2 ---+
|+--------------------------------------- EC-C --------+ |
||+---- Elect.Signature (ES)----+ +--------+| +--------+ |
|||+-------+ +-------+ +-------+| +---------+|Complete|| |Times | |
||||Signa- | |Other | |Digital|| |Timestamp||certs || |Stamp | |
||||ture | |Signed | |Signa- || |over ||and || |over | |
||||Policy | |Attri- | |ture || |digital ||revoc. || |Complete| |
||||ID | |butes | | || |signature||refs || |certs | |
|||+-------+ +-------+ +-------+| +---------+| || |and | |
||+-----------------------------+ +--------+| |revoc. | |
|| | |refs | |
|+-----------------------------------------------------+ +--------+ |
+-------------------------------------------------------------------+
Figure 6: Illustration of ES with ES-X Type 2
2.7 Archive Validation Data
Before the algorithms, keys and other cryptographic data used at the
time the ES-C was built become weak and the cryptographic functions
become vulnerable, or the certificates supporting previous timestamps
expires, the signed data, the ES-C and any additional information
(ES-X) should be timestamped. If possible this should use stronger
algorithms (or longer key lengths) than in the original timestamp.
This additional data and timestamp is called Archive Validation Data
(ES-A). The Timestamping process may be repeated every time the
protection used to timestamp a previous ES-A become weak. An ES-A
may thus bear multiple embedded time stamps.
An example of an Electronic Signature (ES), with the additional
validation data for the ES-C and ES-X forming the ES-A is illustrated
in Figure 7.
+-------------------------------- ES-A --------- ----------+
| +-------------------- ES-A -----------------+ |
| | +--------- ES-X -------------- + | |
| | |..............................| +-----+ | +-----+ |
| | |..............................| |Time | | |Time | |
| | |..............................| |Stamp| | |Stamp| |
| | | | +-----+ | +-----+ |
| | +----------------------------- + | |
| +-------------------------------------------+ |
+----------------------------------------------------------+
Figure 7: Illustration of ES -A
Support for ES-A is optional.
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2.8 Arbitration
The ES-C may be used for arbitration should there be a dispute between
the signer and verifier, provided that:
* a copy of the signature policy referenced by the signer is
available;
* the arbitrator knows where to retrieve the signer's certificate
(if not already present), all the cross-certificates and the
required CRLs and/or OCSPs responses referenced in the ES-C;
* none of the issuing key from the certificate chain have ever
been compromised;
* the cryptography used at the time the ES-C was built has not
been broken at the time the arbitration is performed.
When the second condition is not met, then the plaintiff must provide
an ES-X Long.
When it is known by some external means that the third condition is
not met, then the plaintiff must provide an ES-X Timestamped.
When the two previous conditions are not met, the plaintiff must
provide the two above information (i.e. an ES-X Timestamped and Long).
When the last condition is not met, the plaintiff must provide an
ES-A.
It should be noticed that a verifier may need to get two time stamps
at two different instants of time: one soon after the generation of
the ES and one soon after some grace period allowing any entity from
the certification chain to declare a key compromise.
2.9 Validation Process
The Validation Process validates an electronic signature in accordance
with the requirements of the signature policy. The output status of
the validation process can be:
* valid;
* invalid;
* incomplete verification.
A Valid response indicates that the signature has passed verification
and it complies with the signature validation policy.
A signature validation policy is a part of the signature policy which
specifies the technical requirements on the signer in creating a
signature and verifier when validating a signature.
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An Invalid response indicates that either the signature format is
incorrect or that the digital signature value fails verification
(e.g. the integrity checks on the digital signature value fails or
any of the certificates on which the digital signature verification
depends is known to be invalid or revoked).
An Incomplete Validation response indicates that the format and
digital signature verifications have not failed but there is
insufficient information to determine if the electronic signature
is valid under the signature policy. This can include situations
where additional information, which does not effect the validity of
the digital signature value, may be available but is invalid.
In the case of Incomplete Validation, it may be possible to request
that the electronic signature be checked again at a later date when
additional validation information might become available. Also, in the
case of incomplete validation, additional information may be made
available to the application or user, thus allowing the application or
user to decide what to do with partially correct electronic signatures.
The validation process may also output validation data :
* a signature timestamp;
* the complete validation data;
* the archive validation data.
2.10 Example Validation Sequence
Figure 8, and subsequent description, describes how the validation
process may build up a complete electronic signature over time.
Soon after receiving the electronic signature (ES) from the signer (1),
the digital signature value may be checked, the validation process
must at least add a time-stamp (2), unless the signer has provided one
which is trusted by the verifier. The validation process may also
validate the electronic signature, as required under the identified
signature policy, using additional data (e.g. certificates, CRL, etc.)
provided by trusted service providers. If the validation process is not
complete then the output from this stage is the ES-T.
When all the additional data (e.g. the complete certificate and
revocation information) necessary to validate the electronic signature
first becomes available, then the validation process:
* obtains all the necessary additional certificate and revocation
status information;
* completes all the validation checks on the ES, using the
complete certificate and revocation information (if a timestamp
is not already present, this may be added at the same stage
combining ES-T and ES-C process);
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* records the complete certificate and revocation references (3);
* indicates the validity status to the user (4).
+---------------------------------------- ES-C ----------+
|+----------------------------- ES-T -------+ |
||+--- Elect.Signature (ES) ----+ | +--------+ |
|||+-------+ +-------+ +-------+|+---------+| |Complete| |
||||Signa- | |Other | |Digital|||Timestamp|| |certifi-| |
||||ture | |Signed | |Signa- |||over || |cate and| |
||||Policy | |Attri- | |ture |||digital || |revoca- | |
||||ID | |butes | | |||signature|| |tion | |
|||+-------+ +-------+ +-------+|+---------+| |referen-| |
||+------------\----------------+ ^ | |ces | |
|| \ | | +--------+ |
|| \ 1 / | ^ |
|+----------------\----------------/--------+ | |
+------------------\--------------/-------------- /------+
\ /2 ----3-----/
+----------+ | / /
| Signed |\ v / |
|User data | \ +--------------------+ +------------+
+----------+ \--->| Validation Process |---> |- Valid |
+---|--^-------|--^--+ 4 |- Invalid |
| | | | |- Validation|
v | v | | Incomplete|
+---------+ +--------+ +------------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure 8: Illustration of an ES with Complete validation data (ES-C)
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At the same time as the validation process creates the ES-C, the
validation process may provide and/or record the values of certificates
and revocation status information used in ES-C, called the ES-X Long
(5). This is illustrated in figure 9:
+---------------------------------------------------- ES-X ---------+
|+--------------------------------------- ES-C --------+ +--------+ |
||+--- Elect.Signature (ES) ----+ +--------+ | |Complete| |
|||+-------+ +-------+ +-------+|+---------+|Complete| | |certifi-| |
||||Signa- | |Other | |Digital|||Timestamp||certifi-| | |cate | |
||||ture | |Signed | |Signa- |||over ||cate and| | |and | |
||||Policy | |Attri- | |ture |||digital ||revoca- | | |revoca- | |
||||ID | |butes | | |||signature||tion | | |tion | |
|||+-------+ +---|---+ +-------+|+---------+|referen-| | |Data | |
||+--------------\--------------+ ^ |ces | | +--------+ |
|| \ | +--------+ | ^ |
|| \ 1 2/ ^ | | |
|+------------------\--------------/-----------|-------+ / |
+--------------------\------------/-----------/-------------/-------+
\ / ---3---/ /
+----------+ | / / -----------5-----/
| Signed |\ v | | /
|User data | \ +--------------------+ +-----------+
+----------+ \--->| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure 9: Illustration ES with eXtended validation data (Long)
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When the validation process creates the ES-C it may also create
extended forms of validation data. A first alternative is to timestamp
all data forming the Type 1 X-Timestamp (6). This is illustrated in
figure 10:
+---------------------------------------------------- ES-X -------+
|+--------------------------------------- ES-C --------+ +------+ |
||+--- Elect.Signature (ES) ----+ +--------+ | |Time- | |
|||+-------+ +-------+ +-------+|+---------+|Complete| | |stamp | |
||||Signa- | |Other | |Digital|||Timestamp||certifi-| | |over | |
||||ture | |Signed | |Signa- |||over ||cate and| | |CES | |
||||Policy | |Attri- | |ture |||digital ||revoca- | | +------+ |
||||ID | |butes | | |||signature||tion | | ^ |
|||+-------+ +--|----+ +-------+|+---------+|referen-| | | |
||+-------------|---------------+ ^ |ces | | | |
|| | | +--------+ | | |
|| \ 1 2/ ^ | | |
|+----------------\------------------/---------|-------+ | |
+------------------\----------------/----------/-------------/----+
\ / ----3--/ /
+----------+ | / / --------------6---/
| Signed |\ v | | /
|User data | \ +--------------------+ +-----------+
+----------+ \--->| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure 10: Illustration of ES with eXtended validation data - Type 1 X-
Timestamp
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Another alternative is to timestamp the certificate and revocation
information references used to validate the electronic signature (but
not the signature) (6'); this is called Type 2 X-Timestamped. This is
illustrated in figure 11:
+---------------------------------------------------- ES-X ----------+
|+--------------------------------------- ES-C --------+ +---------+ |
||+--- Elect.Signature (ES) ----+ +--------+ | |Timestamp| |
|||+-------+ +-------+ +-------+|+---------+|Complete| | |over | |
||||Signa- | |Other | |Digital|||Timestamp||certifi-| | |Complete | |
||||ture | |Signed | |Signa- |||over ||cate and| | |Certifi- | |
||||Policy | |Attri- | |ture |||digital ||revoc. | | |cate and | |
||||ID | |butes | | |||signature||refs | | |revoc. | |
|||+-------+ +---^---+ +-------+|+----^----++---^----+ | |refs | |
||+--------------\--------------+ | | | +---------+ |
|+----------------\------------------/----------|------+ ^ |
+----------------1-\----------------/----------/--------------|------+
\ / -----3--/ |
+----------+ | 2/ / --------------6'-----/
| Signed |\ v | | /
|User data | \ +--------------------+ +-----------+
+----------+ \--->| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure 11: Illustration of ES with eXtended validation data - Type 2 X-
Timestamp
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Before the algorithms used in any of electronic signatures become or
are likely, to be compromised or rendered vulnerable in the future, it
is necessary to timestamp the entire electronic signature, including
all the values of the validation and user data as an ES with Archive
validation data (ES-A)
An ES-A is illustrated in figure 12:
-------------------------------------------- ES-A --------------------+
----------------------------------------------------------------+ |
+------------------------------- EC-C --------++-----+ | |
| ||Time-| | |
|+-- Elect.Signature (ES) -+ +--------+||stamp| +-------+ |
||+------++-------++-------|+------+|Complete|||over | Complete| |
|||Signa-||Other ||Digital||Time- ||certifi-|||CES | |certi- |+----|
|||ture ||Signed ||Signa- ||stamp ||cate and||+-----+ |ficate |Arch-|
|||Policy||Attri- ||ture ||over ||revoca- ||+------+ |and |ive |
|||ID ||butes || ||digit.||tion |||Time- | |revoca-|Time |
||+------++---|---++-------||signa-||referen-|||stamp-| |tion |stamp|
|+------------|------------+|ture ||ces |||over | |data |+----|
| | +------++--------+|Complete\+-------+ ^ |
| | ^ ^ ||cert. | | | |
+-------------|----------------|---------|----+|and rev| | | |
\ | / |refs. | | | |
\ | / +-------+ | | |
-----------------\-------------|-------/------------------------+ | |
+----------+ \ | / / |
| Signed | \2 |3 / /--------------7-------/ |
|User data | \ | | / |
+-------\--+ \ | | / |
---------\------------|--------|----|---/-----------------------------+
\ v | | |
1\ +--------------------+ +-----------+
\------>| Validation Process |---> | - Valid |
+---|--^-------|--^--+ 4 | - Invalid |
| | | | +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure 12: Illustration of an ES with Archive validation data (ES-A)
2.11 Additional optional features of an ES
This document also defines additional optional features of
an electronic signature to:
* indicate a commitment type being made by the signer;
* indicate the role under which a signature was created;
* support multiple signatures.
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3. Data structure of an Electronic Signature
This section uses and builds upon the Cryptographic Message Syntax
(CMS), as defined in RFC 2630 [CMS], and Enhanced Security Services
(ESS), as defined in RFC 2634 [ESS]. The overall structure
of Electronic Signature is as defined in [CMS]. The Electronic
Signature (ES) uses attributes defined in [CMS], [ESS] and
this document. This document defines in full the ES attributes which it
uses and are not defined elsewhere.
The mandated set of attributes and the digital signature value is
defined as the minimum Electronic Signature (ES) required by this
document. A signature policy MAY mandate other signed attributes to be
present.
3.1 General Syntax
The general syntax of the ES is as defined in [CMS].
3.2 Data Content Type
The data content type of the ES is as defined in [CMS].
The data content type is intended to refer to arbitrary octet strings,
such as ASCII text files; the interpretation is left to the
application. Such strings need not have any internal structure
(although they could have their own ASN.1 definition or other
structure).
3.3 Signed-data Content Type
The Signed-data content type of the ES is as defined in [CMS].
The signed-data content type consists of a content of any type and zero
or more signature values. Any number of signers in parallel can sign
any type of content. The typical application of the signed-data content
type represents one signer's digital signature on content of the data
content type.
To make sure that the verifier uses the right certificate, this
document mandates that the hash of the signers certificate is always
included in the Signing Certificate signed attribute.
3.4 SignedData Type
The syntax of the SignedData type of the ES is as defined in [CMS].
The fields of type SignedData have the meanings defined [CMS] except
that:
* version is the syntax version number. The value of version must
be 3.
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* The identification of signer's certificate used to create the
signature is always present as a signed attribute.
* The degenerate case where there are no signers is not valid in
this document.
3.5 EncapsulatedContentInfo Type
The syntax of the EncapsulatedContentInfo a type of the ES is as
defined in [CMS].
For the purpose of long term validation as defined by this document, it
is advisable that either the eContent is present, or the data which is
signed is archived in such as way as to preserve the any data encoding.
It is important that the OCTET STRING used to generate the signature
remains the same every time either the verifier or an arbitrator
validates the signature.
The degenerate case where there are no signers is not valid in this
document.
3.6 SignerInfo Type
The syntax of the SignerInfo a type of the ES is as defined in [CMS].
Per-signer information is represented in the type SignerInfo. In the
case of multiple independent signatures, there is an instance
of this field for each signer.
The fields of type SignerInfo have the meanings defined in [CMS]
except that signedAttributes must, as a minimum, contain the following
attributes:
* ContentType as defined in section 3.7.1.
* MessageDigest as defined in section 3.7.2.
* SigningTime as defined in section 3.7.3.
* SigningCertificate as defined in section 3.8.1.
* SignaturePolicyId as defined in section 3.9.1.
3.6.1 Message Digest Calculation Process
The message digest calculation process is as defined in [CMS].
3.6.2 Message Signature Generation Process
The input to the digital signature generation process is as defined in
[CMS].
3.6.3 Message Signature Verification Process
The procedures for CMS signed data validation are as defined in
[CMS] and enhanced in this document.
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The input to the signature verification process includes the signer's
public key verified as correct using either the ESS Signing
Certificate attribute or the Other Signing Certificate attribute.
3.7 CMS Imported Mandatory Present Attributes
The following attributes MUST be present with the signed-data defined
by this document. The attributes are defined in [CMS].
3.7.1 Content Type
The syntax of the content-type attribute type of the ES is as defined
in [CMS].
3.7.2 Message Digest
The syntax of the message-digest attribute type of the ES is as defined
in [CMS].
3.7.3 Signing Time
The syntax of the message-digest attribute type of the ES is as defined
in [CMS] and further qualified by this document.
The signing-time attribute type specifies the time at which the signer
claims to have performed the signing process.
This present document recommends the use of GeneralizedTime.
3.8 Alternative Signing Certificate Attributes
One, and only one, of the following two alternative attributes MUST be
present with the signed-data defined by this document to identify the
signing certificate. Both attributes include an identifier and a hash
of the signing certificate. The first, which is adopted in existing
standards, may be only used with the SHA-1 hashing algorithm. The
other shall be used when other hashing algorithms are to be supported.
The signing certificate attribute is designed to prevent the simple
substitution and re-issue attacks, and to allow for a restricted set of
authorization certificates to be used in verifying a signature.
3.8.1 ESS Signing Certificate Attribute Definition
The syntax of the signing certificate attribute type of the ES is as
defined in [ESS], and further qualified and profile in this document.
The ESS signing certificate attribute must be a signed attribute.
This document mandates the presence of this attribute as a signed CMS
attribute, and the sequence must not be empty. The certificate used to
verify the signature must be identified in the sequence, the Signature
Validation Policy may mandate other certificate references to be
present, that may include all the certificates up to the point of
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trust. The encoding of the ESSCertID for this certificate must include
the issuerSerial field.
The issuerAndSerialNumber present in the SignerInfo must be
consistent with issuerSerial field. The certificate identified must be
used during the signature verification process. If the hash of the
certificate does not match the certificate used to verify the
signature, the signature must be considered invalid.
The sequence of policy information field is not used in this document.
NOTE: Where an attribute certificate is used by the signer to associate
a role, or other attributes of the signer, with the electronic
signature this is placed in the Signer Attribute attribute as defined
in section 3.12.3.
3.8.2 Other Signing Certificate Attribute Definition
The following attribute is identical to the ESS SigningCertificate
defined above except that this attribute can be used with hashing
algorithms other than SHA-1.
This attribute must be used in the same manner as defined above for
the ESS SigningCertificate attribute.
The following object identifier identifies the signing certificate
attribute:
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
The signing certificate attribute value has the ASN.1 syntax
OtherSigningCertificate
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THIS DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL
}
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue
}
OtherHashValue ::= OCTET STRING
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OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}
3.9 Additional Mandatory Attributes
3.9.1 Signature policy Identifier
This document mandates that a reference to the signature policy, is
included in the signedData, this reference is either explicitly
identified or implied by the semantics of the signed content and other
external data. A signature policy defines the rules for creation and
validation of an electronic signature, is included as a signed
attribute with every signature. The signature policy identifier must be
a signed attribute.
The following object identifier identifies the signature policy
identifier attribute:
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
Signature-policy-identifier attribute values have ASN.1 type
SignaturePolicyIdentifier.
SignaturePolicyIdentifier ::= CHOICE{
SignaturePolicyId SignaturePolicyId,
SignaturePolicyImplied SignaturePolicyImplied }
SignaturePolicyId ::= SEQUENCE {
sigPolicyIdentifier SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
The presence of the NULL type indicates that the signature policy is
implied by the semantics of the signed data and other external data.
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The sigPolicyId field contains an object-identifier which
uniquely identifies a specific version of the signature policy. The
syntax of this field is as follows:
SigPolicyId ::= OBJECT IDENTIFIER
The sigPolicyHash field contains the identifier of the hash algorithm
and the hash of the value of the signature policy.
If the signature policy is defined using a computer processable
notation like ASN.1, then the hash is calculated on the value without
the outer type and length fields and the hashing algorithm must be as
specified in the field signPolicyHshAlg.
If the signature policy is defined using another structure, the type of
structure and the hashing algorithm must be either specified as part
of the signature policy, or indicated using a signature policy
qualifier.
SigPolicyHash ::= ETSIHashAlgAndValue
A signature policy identifier may be qualified with other information
about the qualifier. The semantics and syntax of the qualifier is as
associated with the object-identifier in the sigPolicyQualifierId
field. The general syntax of this qualifier is as follows:
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId
}
This document specifies the following qualifiers:
* spuri: This contains the web URI or URL reference to the
signature policy
* spUserNotice: This contains a user notice which should be
displayed whenever the signature is validated.
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-- sigpolicyQualifierIds defined in this document
SigPolicyQualifierId ::= OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL
}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER
}
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200))
}
3.10 CMS Imported Optional Attributes
The following attributes MAY be present with the signed-data defined by
this document. The attributes are defined in ref [CMS] and are imported
into this specification and were appropriate qualified and profiling by
this document.
3.10.1 Countersignature
The syntax of the countersignature attribute type of the ES is as
defined in [CMS]. The countersignature attribute must be an unsigned
attribute.
3.11 ESS Imported Optional Attributes
The following attributes MAY be present with the signed-data defined by
this document. The attributes are defined in ref [ESS] and are imported
into this specification and were appropriate qualified and profiling
by this document.
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3.11.1 Content Reference Attribute
The content reference attribute is a link from one SignedData to
another. It may be used to link a reply to the original message to
which it refers, or to incorporate by reference one SignedData into
another.
The content reference attribute MUST be used as defined in [ESS]. The
content reference MUST be a signed attribute.
The syntax of the content reference attribute type of the ES is as
defined in [ESS].
3.11.2 Content Identifier Attribute
The content identifier attribute provides an identifier for the signed
content for use when reference may be later required to that content,
for example in the content reference attribute in other signed data
sent later.
The content identifier must be a signed attribute.
The syntax of the content identifier attribute type of the ES is as
defined in [ESS].
The minimal signedContentIdentifier should contain a concatenation of
user-specific identification information (such as a user name or public
keying material identification information), a GeneralizedTime string,
and a random number.
3.11.3 Content Hints Attribute
The content hints attribute provides information that describes the
format of the signed content. It may be used by the signer to indicate
to a verifier the precise format that MUST be used to present the data
(e.g. text, voice, video) to a verifier. This attribute MUST be
present when it is mandatory to present the signed data to human users
on verification.
The syntax of the content hints attribute type of the ES is as defined
in ESS (RFC 2634, section 2.9 [9]).
When used to indicate the precise format of the data to be presented to
the user the following rules apply:
The contentType (defined in RFC 2630 [8]) indicates the type of the
associated content. It is an object identifier (i.e. a unique string of
integers) assigned by an authority that defines the content type.
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The UTF8String shall define the presentation format. The format may be
defined by MIME types as indicated below.
Note 1: The contentType can be id-data defined in CMS (RFC 2630 [8]).
The UTF8String can be used to indicate the encoding of the data, like
MIME type. RFC 2045 [25] provides a common structure for encoding a
range of electronic documents and other multi-media types, see annex B
for further information, a system supporting verification of electronic
signature may present information to users in the form identified by
the MIME type.
id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs7(7) 1 }
3.12 Additional Optional Attributes
3.12.1 Commitment Type Indication Attribute
There may be situation were a signer wants to explicitly indicate to a
verifier that by signing the data, it illustrates a type of commitment
on behalf of the signer. The commitmentTypeIndication attribute conveys
such information.
The commitmentTypeIndication attribute must be a signed attribute.
The commitment type may be:
* defined as part of the signature policy, in which case the
commitment type has precise semantics that is defined as part of
the signature policy.
* be a registered type, in which case the commitment type has
precise semantics defined by registration, under the rules of the
registration authority. Such a registration authority may be a
trading association or a legislative authority.
The signature policy specifies a set of attributes that it
"recognizes". This "recognized" set includes all those commitment types
defined as part of the signature policy as well as any externally
defined commitment types that the policy may choose to recognize. Only
recognized commitment types are allowed in this field.
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The following object identifier identifies the commitment type
indication attribute:
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
Commitment-Type-Indication attribute values have ASN.1 type
CommitmentTypeIndication.
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL
}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY
commitmentTypeIdentifier
}
The use of any qualifiers to the commitment type is outside the scope
of this document.
The following generic commitment types are defined in this document:
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 6}
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These generic commitment types have the following meaning:
Proof of origin indicates that the signer recognizes to have created,
approved and sent the message.
Proof of receipt indicates that signer recognizes to have received the
content of the message.
Proof of delivery indicates that the TSP providing that indication has
delivered a message in a local store accessible to the recipient of the
message.
Proof of sender indicates that the entity providing that indication has
sent the message (but not necessarily created it).
Proof of approval indicates that the signer has approved the content of
the message.
Proof of creation indicates that the signer has created the message
(but not necessarily approved, nor sent it).
3.12.2 Signer Location attribute
The signer-location attribute is an attribute which specifies a
mnemonic for an address associated with the signer at a particular
geographical (e.g. city) location. The mnemonic is registered in the
country in which the signer is located and is used in the provision of
the Public Telegram Service (according to ITU-T Recommendation F.1
[PTS]).
The signer-location attribute must be a signed attribute.
The following object identifier identifies the signer-location
attribute:
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
Signer-location attribute values have ASN.1 type SignerLocation.
SignerLocation ::= SEQUENCE {
-- at least one of the following must be present
countryName [0] DirectoryString OPTIONAL,
-- as used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- as used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL
}
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
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3.12.3 Signer Attributes attribute
The signer-attributes attribute is an attribute which specifies
additional attributes of the signer (e.g. role).
It may be either:
* claimed attributes of the signer; or
* certified attributes of the signer;
The signer-attributes attribute must be a signed attribute.
The following object identifier identifies the signer-attribute
attribute:
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
signer-attribute attribute values have ASN.1 type SignerAttribute.
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes
}
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in X.509 : see section 10.3
NOTE: The claimed and certified attribute are imported from ITU-T
Recommendations X.501 [16] and ITU-T Recommendation X.509 : Draft
Amendment on Certificate Extensions, October 1999.
3.12.4 Content Timestamp attribute
The content timestamp attribute is an attribute which is the timestamp
of the signed data content before it is signed.
The content timestamp attribute must be a signed attribute.
The following object identifier identifies the signer-attribute
attribute:
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
Content timestamp attribute values have ASN.1 type ContentTimestamp:
ContentTimestamp::= TimeStampToken
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The value of messageImprint field within TimeStampToken must be a hash
of the value of eContent field within encapContentInfo within the
signedData.
For further information and definition of TimeStampToken see [TSP].
3.13 Support for Multiple Signatures
3.13.1 Independent Signatures
Multiple independent signatures are supported by independent SignerInfo
from each signer.
Each SignerInfo must include all the attributes required under this
document and must be processed independently by the verifier.
3.13.2 Embedded Signatures
Multiple embedded signatures are supported using the counter-signature
unsigned attribute (see section 3.10.1). Each counter signature is
carried in Countersignature held as an unsigned attribute to the
SignerInfo to which the counter-signature is applied.
4. Validation Data
This section specifies the validation data structures which builds on
the electronic signature specified in section 3. This includes:
* Timestamp applied to the electronic signature value.
* Complete validation data which comprises the timestamp of the
signature value, plus references to all the certificates and
revocation information used for full validation of the electronic
signature.
The following optional eXtended forms of validation data are also
defined:
* X-timestamp: There are two types of timestamp used in extended
validation data defined by this document.
- Type 1 -Timestamp which comprises a timestamp over the ES
with Complete validation data (ES-C).
- Type 2 X-Timestamp which comprises of a timestamp over the
certification path references and the revocation information
references used to support the ES-C.
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* X-Long : This comprises a Complete validation data
plus the actual values of all the certificates and
revocation information used in the ES-C.
* X-Long-Timestamp: This comprises a Type 1 or Type 2
X-Timestamp plus the actual values of all the
certificates and revocation information used in the
ES-C.
This section also specifies the data structures used in Archive
validation data:
* Archive validation data comprises a Complete validation data,
the certificate and revocation values (as in a X-Long
validation data), any other existing X-timestamps, plus the
Signed User data and an additional archive timestamp over all
that data. An archive timestamp may be repeatedly applied
after long periods to maintain validity when electronic
signature and timestamping algorithms weaken.
The additional data required to create the forms of electronic
signature identified above is carried as unsigned attributes
associated with an individual signature by being placed in the
unsignedAttrs field of SignerInfo. Thus all the attributes defined
in section 4 are unsigned attributes.
NOTE: Where multiple signatures are to be supported, as described in
section 3.13, each signature has a separate SignerInfo. Thus, each
signature requires its own unsigned attribute values to create ES-T,
ES-C etc.
4.1 Electronic Signature Timestamp
An Electronic Signature with Timestamp is an Electronic Signature for
which part, but not all, of the additional data required for validation
is available (e.g. some certificates and revocation information is
available but not all).
The minimum structure Timestamp validation data is the Signature
Timestamp Attribute as defined in section 4.1.1 over the ES signature
value.
4.1.1 Signature Timestamp Attribute Definition
The Signature Timestamp attribute is timestamp of the signature value.
It is an unsigned attribute. Several instances of this attribute from
different TSAs may occur with an electronic signature.
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The Signature Validation Policy specifies, in the
signatureTimestampDelay field of TimestampTrustConditions, a maximum
acceptable time difference which is allowed between the time indicated
in the signing time attribute and the time indicated by the Signature
Timestamp attribute. If this delay is exceeded then the electronic
signature must be considered as invalid.
The following object identifier identifies the Signature Timestamp
attribute:
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 14}
The Signature timestamp attribute value has ASN.1 type
SignatureTimeStampToken.
SignatureTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken must be a hash
of the value of signature field within SignerInfo for the signedData
being timestamped.
For further information and definition of TimeStampToken see [TSP]
4.2 Complete Validation Data
An electronic signature with complete validation data is an Electronic
Signature for which all the additional data required for validation
(i.e. all certificates and revocation information) is available.
Complete validation data (ES-C) build on the electronic signature
Timestamp as defined above.
The minimum structure of a Complete validation data is:
* the Signature Timestamp Attribute, as defined in section 4.1.1;
* Complete Certificate Refs, as defined in section 4.2.1;
* Complete Revocation Refs, as defined in section 4.2.2.
The Complete validation data MAY also include the following additional
information, forming a X-Long validation data, for use if later
validation processes may not have access to this information:
* Complete Certificate Values, as defined in section 4.2.3;
* Complete Revocation Values, as defined in section 4.2.4.
The Complete validation data MAY also include one of the following
additional attributes, forming a X-Timestamp validation data, to
provide additional protection against later CA compromise and provide
integrity of the validation data used:
* ES-C Timestamp, as defined in section 4.2.5; or
* Time-Stamped Certificates and CRLs references, as defined in
section 4.2.6.
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NOTE 1: As long as the CA's are trusted such that these keys cannot
be compromised or the cryptography used broken, the ES-C provides long
term proof of a valid electronic signature.
A valid electronic signature is an electronic signature which passes
validation according to a signature validation policy.
NOTE 2: The ES-C provides the following important property for long
standing signatures; that is having been found once to be valid, must
continue to be so months or years later. Long after the validity period
of the certificates have expired, or after the user key has been
compromised.
4.2.1 Complete Certificate Refs Attribute Definition
The Complete Certificate Refs attribute is an unsigned attribute. It
references the full set of CA certificates that have been used to
validate a ES with Complete validation data (ES-C) up to (but not
including) the signer's certificate. Only a single instance of this
attribute must occur with an electronic signature.
Note: The signer's certified is referenced in the signing certificate
attribute (see section 3.1).
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
The complete certificate refs attribute value has the ASN.1 syntax
CompleteCertificateRefs.
CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID
OTHERCertID is defined in section 3.8.2.
The IssuerSerial that must be present in OTHERCertID. The certHash
must match the hash of the certificate referenced.
NOTE: Copies of the certificate values may be held using the
Certificate Values attribute defined in section 4.3.1.
4.2.2 Complete Revocation Refs Attribute Definition
The Complete Revocation Refs attribute is an unsigned attribute. Only a
single instance of this attribute must occur with an electronic
signature. It references the full set of the CRL or OCSP responses that
have been used in the validation of the signer and CA certificates
used in ES with Complete validation data.
The following object identifier identifies the CompleteRevocationRefs
attribute:
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
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The complete revocation refs attribute value has the ASN.1 syntax
CompleteRevocationRefs.
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CompleteRevocationRefs must contain one CrlOcspRef for the signing
certificate, followed by one for each OTHERCertID in the
CompleteCertificateRefs attribute. The second and subsequent CrlOcspRef
fields must be in the same order as the OTHERCertID to which they
relate. At least one of CRLListID or OcspListID or OtherRevRefs should
be present for all but the "trusted" CA of the certificate path.
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash ETSIHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash ETSIHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}
When creating an crlValidatedID, the crlHash is computed over the
entire DER encoded CRL including the signature. The crlIdentifier would
normally be present unless the CRL can be inferred from other
information.
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The crlIdentifier is to identify the CRL using the issuer name and the
CRL issued time which must correspond to the time "thisUpdate"
contained in the issued CRL. The crlListID attribute is an unsigned
attribute. In the case that the identified CRL is a Delta CRL then
references to the set of CRLs to provide a complete revocation list
must be included.
The OcspIdentifier is to identify the OSCP response using the issuer
name and the time of issue of the OCSP response which must correspond
to the time "producedAt" contained in the issued OCSP response. Since
it may be needed to make the difference between two OCSP responses
received within the same second, then the hash of the response
contained in the OcspResponsesID may be needed to solve the ambiguity.
NOTE: Copies of the CRL and OCSP responses values may be held using
the Revocation Values attribute defined in section 4.3.2.
OtherRevRefs ::= SEQUENCE {
otherRevRefType OtherRevRefType,
otherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIER
The syntax and semantics of other revocation references is outside the
scope of this document. The definition of the syntax of the other form
of revocation information is as identified by OtherRevRefType.
4.3 Extended Validation Data
4.3.1 Certificate Values Attribute Definition
The Certificate Values attribute is an unsigned attribute. Only a
single instance of this attribute must occur with an electronic
signature. It holds the values of certificates referenced in the
CompleteCertificateRefs attribute.
Note: If an Attribute Certificate is used, it is not provided in this
structure but must be provided by the signer as a signer-attributes
attribute (see section 12.3).
The following object identifier identifies the CertificateValues
attribute:
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
The certificate values attribute value has the ASN.1 syntax
CertificateValues.
CertificateValues ::= SEQUENCE OF Certificate
Certificate is defined in RFC2459 and ITU-T Recommendation X.509 [1])
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4.3.2 Revocation Values Attribute Definition
The Revocation Values attribute is an unsigned attribute. Only a single
instance of this attribute must occur with an electronic signature. It
holds the values of CRLs and OCSP referenced in the
CompleteRevocationRefs attribute.
The following object identifier identifies the Revocation Values
attribute:
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 24}
The revocation values attribute value has the ASN.1 syntax
RevocationValues.
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals
}
OtherRevVals ::= SEQUENCE {
otherRevValType OtherRevValType,
otherRevVals ANY DEFINED BY otherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIER
The syntax and semantics of the other revocation values is outside the
scope of this document. The definition of the syntax of the other form
of revocation information is as identified by OtherRevRefType.
CertificateList is defined in RFC 2459 [RFC2459] and in ITU-T
Recommendation X.509 [X509]).
BasicOCSPResponse is defined in RFC 2560 [OCSP].
4.3.3 ES-C Timestamp Attribute Definition
This attribute is used for the Type 1 X-Timestamped validation data.
The ES-C Timestamp attribute is an unsigned attribute. It is timestamp
of a hash of the electronic signature and the complete validation data
(ES-C). It is a special purpose TimeStampToken Attribute which
timestamps the ES-C. Several instances instance of this attribute may
occur with an electronic signature from different TSAs.
The following object identifier identifies the ES-C Timestamp
attribute:
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 25}
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The ES-C timestamp attribute value has the ASN.1 syntax
ESCTimeStampToken.
ESCTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken must be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the ES with
Complete validation data (ES-C):
* signature field within SignerInfo;
* SignatureTimeStampToken attribute;
* CompleteCertificateRefs attribute;
* CompleteRevocationRefs attribute.
For further information and definition of the Time Stamp Token see
[TSP].
4.3.4 Time-Stamped Certificates and CRLs Attribute Definition
This attribute is used for the Type 2 X-Timestamp validation data. A
TimestampedCertsCRLsRef attribute is an unsigned attribute. It is a
list of referenced certificates and OCSP responses/CRLs which are been
timestamped to protect against certain CA compromises. Its syntax is as
follows:
The following object identifier identifies the TimestampedCertsCRLsRef
attribute:
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 26}
The attribute value has the ASN.1 syntax TimestampedCertsCRLs.
TimestampedCertsCRLs ::= TimeStampToken
The value of messageImprint field within TimeStampToken must be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the ES with
Complete validation data (ES-C):
* CompleteCertificateRefs attribute;
* CompleteRevocationRefs attribute.
4.4 Archive Validation Data
Where an electronic signature is required to last for a very long time,
and a the timestamp on an electronic signature is in danger of being
invalidated due to algorithm weakness or limits in the validity period
of the TSA certificate, then it may be required to timestamp the
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 39]
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electronic signature several times. When this is required an archive
timestamp attribute may be required. This timestamp may be repeatedly
applied over a period of time.
4.4.1 Archive Timestamp Attribute Definition
The Archive Timestamp attribute is timestamp of the user data and the
entire electronic signature. If the Certificate values and Revocation
Values attributes are not present these attributes must be added to
the electronic signature prior to the timestamp. The Archive Timestamp
attribute is an unsigned attribute. Several instances of this attribute
may occur with on electronic signature both over time and from
different TSAs.
The following object identifier identifies the Nested Archive Timestamp
attribute:
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 27}
Archive timestamp attribute values have the ASN.1 syntax
ArchiveTimeStampToken
ArchiveTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken must be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the electronic
signature:
* encapContentInfo eContent OCTET STRING;
* signedAttributes;
* signature field within SignerInfo;
* SignatureTimeStampToken attribute;
* CompleteCertificateRefs attribute;
* CompleteRevocationData attribute;
* CertificateValues attribute
(If not already present this information must be included in
the ES-A);
* RevocationValues attribute
(If not already present this information must be included in
the ES-A);
* ESCTimeStampToken attribute if present;
* TimestampedCertsCRLs attribute if present;
* any previous ArchiveTimeStampToken attributes.
For further information and definition of TimeStampToken see [TSP]
The timestamp should be created using stronger algorithms (or longer
key lengths) than in the original electronic signatures.
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5. Security considerations
5.1 Protection of Private Key
The security of the electronic signature mechanism defined in this
document depends on the privacy of the signer's private key.
Implementations must take steps to ensure that private keys cannot be
compromised.
5.2 Choice of Algorithms
Implementers should be aware that cryptographic algorithms become
weaker with time. As new cryptoanalysis techniques are developed and
computing performance improves, the work factor to break a particular
cryptographic algorithm will reduce. Therefore, cryptographic algorithm
implementations should be modular allowing new algorithms to be readily
inserted. That is, implementers should be prepared for the set of
mandatory to implement algorithms to change over time.
6. Conformance Requirements
This document only defines conformance requirements up to a ES with
Complete validation data (ES-C). This means that none of the extended
and archive forms of Electronic Signature (ES-X, ES-A) need to be
implemented to get conformance to this standard.
This document mandates support for elements of the signature policy.
6.1 Signer
A system supporting signers according to this document must, at a
minimum, support generation of an electronic signature consisting of
the following components:
* The general CMS syntax and content type as defined in RFC 2630
(see sections 4.1 and 4.2).
* CMS SignedData as defined in RFC 2630 with version set to 3
and at least one SignerInfo must be present
(see sections 4.3, 4.4, 4.5, 4.6).
* The following CMS Attributes as defined in RFC 2630 :
- ContentType; This must always be present
(see section 3.7.1);
- MessageDigest; This must always be present
(see section 3.7.2);
- SigningTime; This must always be present
(see section 3.7.3).
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* The following ESS Attributes as defined in RFC 2634 :
- SigningCertificate: This must be set as defined
in sections 3.8.1 and 3.8.2.
* The following Attributes as defined in section 3.9:
- SignaturePolicyIdentifier; This must always be present.
* Public Key Certificates as defined in ITU-T Recommendation
X.509 [1] and profiled in RFC 2459 [7] (see section 9.1).
6.2 Verifier using timestamping
A system supporting verifiers according to this document with
timestamping facilities must, at a minimum, support:
* Verification of the mandated components of an electronic
signature, as defined in section 5.1.
* Signature Timestamp attribute, as defined in section 4.1.1.
* Complete Certificate Refs attribute, as defined in
section 4.2.1.
* Complete Revocation Refs Attribute, as defined in
section 4.2.2.
* Public Key Certificates, as defined in ITU-T
Recommendation X.509 and profiled in RFC 2459.
* Either of:
- Certificate Revocation Lists. as defined in ITU-T
Recommendation X.509 [1] and profiled in RFC 2459 [7];
or
- On-line Certificate Status Protocol responses, as
defined in RFC 2560.
6.3 Verifier using secure records
A system supporting verifiers according to the present document shall,
at a minimum, support:
* Verification of the mandated components of an electronic
signature, as defined in subsection 5.1.
* Complete Certificate Refs attribute, as defined in
subsection 4.2.1.
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* Complete Revocation Refs Attribute, as defined in
subsection 9.2.2.
* A record shall be maintained, which cannot be undetectably
modified, of the electronic signature and the time when the
signature was first validated using the referenced
certificates and revocation information.
* Public Key Certificates, as defined in ITU-T Recommendation
X.509 [1] and profiled in RFC 2459 [7] (see subsection 10.1).
* Either of:
- Certificate Revocation Lists. as defined in ITU-T
Recommendation X.509 [1] and profiled in RFC 2459 [7]
Or
- On-line Certificate Status Protocol, as defined
in RFC 2560 [8] (see subsection 10.3).
7. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ESS] P. Hoffman, "Enhanced Security Services for S/MIME",
RFC 2634, June 1999
[CMS] R. Housley, "Cryptographic Message Syntax", RFC 2630,
June 1999.
[OCSP] M. Myers, R. Ankney, A. Malpani, S. Galperin, C. Adams.
On-line Status Certificate Protocol, RFC 2560.
[TSP] C. Adams, P. Cain, D. Pinkas, R. Zuccherato. Time Stamp Protocol
(TSP), (under progress). June 2000.
[PTS] Public Telegram Service. ITU-T Recommendation F1. XXXX
[RFC2459] R. Housley, W. Ford, W. Polk, D. Solo, "Internet X.509 Public
Key Infrastructure, Certificate and CRL Profile," RFC 2459, January
1999.
[PKCS9] RSA Laboratories, "The Public-Key Cryptography Standards
(PKCS)", RSA Data Security Inc., Redwood City, California, November
1993 Release.
[ISONR] ISO/IEC 10181-5: Security Frameworks in Open Systems.
Non-Repudiation Framework. April 1997.
[ES201733] ETSI Standard ES 201 733 V1.1.3 (2000-05) Electronic
Signature Formats. Note: copies of ETSI ES 210 733 can be freely
downloaded from the ETSI web site www.etsi.org.
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8. Authors' Addresses
This Informational RFC has been produced in ETSI TC-SEC.
ETSI
F-06921 Sophia Antipolis, Cedex - FRANCE
650 Route des Lucioles - Sophia Antipolis
Valbonne - France
Tel: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16
secretariat@etsi.fr
http://www.etsi.org
Contact Point
Harri Rasilainen
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis, Cedex
FRANCE
harri.rasilainen@etsi.fr
Denis Pinkas
Bull S.A.
12, rue de Paris
B.P. 59
78231 Le Pecq
FRANCE
Denis.Pinkas @bull.net
John Ross
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
ross@secstan.com
Nick Pope
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
pope@secstan.com
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9. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights defined
in the Internet Standards process must be followed, or as required to
translate it into languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Annex A (normative): ASN.1 Definitions
This annex provides a summary of all the ASN.1 syntax definitions for
new syntax defined in this document.
A.1 Definitions Using X.208 (1988) ASN.1 Syntax
NOTE: The ASN.1 module defined in section A.1 has precedence over that
defined in Annex A-2 in the case of any conflict.
ETS-ElectronicSignatureFormats-88syntax { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 5}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All -
IMPORTS
-- Crypographic Message Syntax (CMS): RFC 2630
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime, SigningTime,
id-countersignature, Countersignature
FROM CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms(1) }
-- ESS Defined attributes: RFC 2634
-- (Enhanced Security Services for S/MIME)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference,
id-aa-contentIdentifier, ContentIdentifier
FROM ExtendedSecurityServices
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }
-- Internet X.509 Public Key Infrastructure
-- Certificate and CRL Profile: RFC 2459
Certificate, AlgorithmIdentifier, CertificateList, Name,
GeneralNames, GeneralName, DirectoryString,Attribute,
AttributeTypeAndValue, AttributeType, AttributeValue,
PolicyInformation, BMPString, UTF8String
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 46]
Internet Draft Electronic Signature Formats
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit-
88(1)}
-- X.509 '97 Authentication Framework
AttributeCertificate
FROM AuthenticationFramework
{joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}
-- The imported AttributeCertificate is defined using the X.680 1997
-- ASN.1 Syntax,
-- an equivalent using the 88 ASN.1 syntax may be used.
-- OCSP 2560
BasicOCSPResponse, ResponderID
FROM OCSP {-- OID not assigned -- }
-- Time Stamp Protocol Internet Draft
TimeStampToken
FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
-- S/MIME Object Identifier arcs used in this document
-- ===================================================
-- S/MIME OID arc used in this document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
-- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }
-- S/MIME Arcs
-- id-mod OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 47]
Internet Draft Electronic Signature Formats
-- Definitions of Object Identifier arcs used in this document
-- ===========================================================
-- The allocation of OIDs to specific objects are given below with the
-- associated ASN.1 syntax definition
-- OID used referencing electronic signature mechanisms based on this
-- standard for use with the IDUP API (see annex D)
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1)
idupMechanism (4)etsiESv1(1) }
-- CMS Attributes Defined in this document
-- =======================================
-- Mandatory Electronic Signature Attributes
-- OtherSigningCertificate
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THIS DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL
}
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue
}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 48]
Internet Draft Electronic Signature Formats
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
"SignaturePolicy CHOICE {
SignaturePolicyId SignaturePolicyId,
SignaturePolicyImplied SignaturePolicyImplied
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyIdentifier SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= ETSIHashAlgAndValue
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId
}
SigPolicyQualifierId ::=
OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 49]
Internet Draft Electronic Signature Formats
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL
}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER
}
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200))
}
-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL
}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier
}
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 3}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 50]
Internet Draft Electronic Signature Formats
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following must be present
countryName [0] DirectoryString OPTIONAL,
-- as used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- as used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL
}
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes
}
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate -- as defined in X.509 :
see section 10.3
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 51]
Internet Draft Electronic Signature Formats
-- Content Timestamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 20}
ContentTimestamp::= TimeStampToken
-- Validation Data
-- Signature Timestamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID
-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash ETSIHash,
crlIdentifier CrlIdentifier OPTIONAL
}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 52]
Internet Draft Electronic Signature Formats
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash ETSIHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- as in OCSP response data
producedAt GeneralizedTime
-- as in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OtherRevRefType,
otherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIER
-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals
}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 53]
Internet Draft Electronic Signature Formats
OtherRevVals ::= SEQUENCE {
otherRevValType OtherRevValType,
otherRevVals ANY DEFINED BY otherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIER
-- ES-C Timestamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Timestamp
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 27}
ArchiveTimeStampToken ::= TimeStampToken
END -- ETS-ElectronicSignatureFormats-88syntax --
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 54]
Internet Draft Electronic Signature Formats
A.2 Definitions Using X.680 1997 ASN.1 Syntax
NOTE: The ASN.1 module defined in section A.1 has precedence over that
defined in section A.2 in the case of any conflict.
ETS-ElectronicSignatureFormats-97Syntax { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 6}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All -
IMPORTS
-- Cryptographic Message Syntax (CMS): RFC 2630
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime,
SigningTime, id-countersignature, Countersignature
FROM CryptographicMessageSyntax
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms(1) }
-- ESS Defined attributes: RFC 2634 (Enhanced Security Services
-- for S/MIME)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference,
id-aa-contentIdentifier, ContentIdentifier
FROM ExtendedSecurityServices
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }
-- Internet X.509 Public Key Infrastructure
- - Certificate and CRL Profile:RFC 2459
Certificate, AlgorithmIdentifier, CertificateList, Name,
GeneralNames, GeneralName, DirectoryString, Attribute,
AttributeTypeAndValue, AttributeType, AttributeValue,
PolicyInformation.
FROM PKIX1Explicit93
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit-88(1)}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 55]
Internet Draft Electronic Signature Formats
-- X.509 '97 Authentication Framework
AttributeCertificate
FROM AuthenticationFramework
{joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3}
-- OCSP 2560
BasicOCSPResponse, ResponderID
FROM OCSP
-- { OID not assigned }
-- Time Stamp Protocol Internet Draft TimeStampToken
FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
-- S/MIME Object Identifier arcs used in this document
-- ===================================================
-- S/MIME OID arc used in this document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
-- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }
-- S/MIME Arcs
-- id-mod OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier
-- Definitions of Object Identifier arcs used in this document
-- ===========================================================
-- The allocation of OIDs to specific objects are given below with the
-- associated ASN.1 syntax definition
-- OID used referencing electronic signature mechanisms based on this
-- standard for use with the IDUP API (see annex D)
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 56]
Internet Draft Electronic Signature Formats
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1)
idupMechanism (4)etsiESv1(1) }
-- CMS Attributes Defined in this document
-- =======================================
-- Mandatory Electronic Signature Attributes
-- OtherSigningCertificate
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THIS DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL
}
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue
}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
"SignaturePolicy CHOICE {
SignaturePolicyId SignaturePolicyId,
SignaturePolicyImplied SignaturePolicyImplied
}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 57]
Internet Draft Electronic Signature Formats
SignaturePolicyId ::= SEQUENCE {
sigPolicyIdentifier SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= ETSIHashAlgAndValue
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SIG-POLICY-QUALIFIER.&id
({SupportedSigPolicyQualifiers}),
qualifier SIG-POLICY-QUALIFIER.&Qualifier
({SupportedSigPolicyQualifiers}
{@sigPolicyQualifierId})OPTIONAL }
SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::=
{ noticeToUser | pointerToSigPolSpec }
SIG-POLICY-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
SIG-POLICY-QUALIFIER-ID &id
[SIG-QUALIFIER-TYPE &Qualifier] }
noticeToUser SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-sqt-unotice SIG-QUALIFIER-TYPE
SPUserNotice
}
pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-sqt-uri SIG-QUALIFIER-TYPE SPuri }
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 58]
Internet Draft Electronic Signature Formats
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL
}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER
}
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200))
}
-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier
OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentQualifierId COMMITMENT-QUALIFIER.&id,
qualifier COMMITMENT-QUALIFIER.&Qualifier
OPTIONAL }
COMMITMENT-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
COMMITMENT-QUALIFIER-ID &id
[COMMITMENT-TYPE &Qualifier] }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 1}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 59]
Internet Draft Electronic Signature Formats
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following must be present
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- As defined in X.509 : see section 10.3
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 60]
Internet Draft Electronic Signature Formats
-- Content Timestamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
ContentTimestamp::= TimeStampToken
-- Validation Data
-- Signature Timestamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OTHERCertID
-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash ETSIHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 61]
Internet Draft Electronic Signature Formats
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash ETSIHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OTHER-REVOCATION-REF.&id,
otherRevRefs OTHER-REVOCATION-REF.&Type
}
OTHER-REVOCATION-REF ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
&Type ID &id }
-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals }
OtherRevVals ::= SEQUENCE {
otherRevValType OTHER-REVOCATION-VAL.&id,
otherRevVals OTHER-REVOCATION-VAL.&Type
}
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OTHER-REVOCATION-VAL ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
&Type ID &id }
-- ES-C Timestamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Timestamp
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 27}
ArchiveTimeStampToken ::= TimeStampToken
END -- ETS-ElectronicSignatureFormats-97Syntax
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Annex B (informative): General Description
This annex captures the concepts that apply to this document and the
rational for the elements of the specification defined using ASN.1 in
the main text of this document.
The specification below includes a description why the component is
needed, with a brief description of the vulnerabilities and threats
and the manner by which they are countered.
B.1 The Signature Policy
The signature policy is a set of rules for the creation and validation
of an electronic signature, under which the signature can be
determined to be valid. A given legal/contractual context may
recognize a particular signature policy as meeting its requirements.
A signature policy may be issued, for example, by a party relying on
the electronic signatures and selected by the signer for use with that
relying party. Alternatively, a signature policy may be established
through an electronic trading association for use amongst its members.
Both the signer and verifier use the same signature policy.
The signature policy may be explicitly identified or may be implied by
the semantics of the data being signed and other external data like a
contract being referenced which itself refers to a signature policy.
An explicit signature policy has a globally unique reference, which is
bound to an electronic signature by the signer as part of the signature
calculation.
The signature policy needs to be available in human readable form so
that it can be assessed to meet the requirements of the legal and
contractual context in which it is being applied. To facilitate the
automatic processing of an electronic signature the parts of the
signature policy which specify the electronic rules for the creation
and validation of the electronic signature also needs to be in a
computer processable form.
The signature policy thus includes the following:
* Information about the signature policy that can be displayed
to the signer or the verifiers.
* Rules, which apply to functionality, covered by this document
(referred to as the Signature Validation Policy).
* Rules which may be implied through adoption of Certificate
Policies that apply to the electronic signature (e.g. rules for
ensuring the secrecy of the private signing key).
* Rules, which relate to the environment used by the signer,
e.g. the use of an agreed CAD (Card Accepting Device) used
in conjunction with a smart card.
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An explicit Signature Validation Policy may be structured so that it
can be computer processable. Any format of the signature validation
policy is allowed by this document. However, for a given explicit
signature policy there must be one definitive form that has a unique
binary encoded value.
The Signature Validation Policy includes rules regarding use of TSPs
(CA, Attribute Authorities, Time Stamping Authorities) as well as
rules defining the components of the electronic signature that must be
provided by the signer with data required by the verifier to provide
long term proof.
B.2 Signed Information
The information being signed may be defined as a MIME-encapsulated
message which can be used to signal the format of the content in order
to select the right display or application. It can be composed of
formatted text (e.g. EDIFACT), free text or of fields from an
electronic form (e-form). For example, the Adobe(tm) format "pdf" may
be used or the eXtensible Mark up Language (XML).
B.3 Components of an Electronic Signature
B.3.1 Reference to the Signature Policy
The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a "Signature policy", at a given time,
by a signer under an identifier, e.g. a name or a pseudonym, and
optionally a role".
When two independent parties want to evaluate an electronic signature,
it is fundamental that they get the same result. To meet this
requirement same signature policy must be used by the signer and
verifier.
The signature policy may be explicitly identified or may be implied by
the semantics of the data being signed and other external data which
designate the signature policy to be used.
By signing over the signature policy identifier the signer explicitly
indicates that he or she has applied the signature policy in creating
the signature. Thus, undertakes any explicit or implied commitments.
In order to unambiguously identify an explicit signature policy that is
to be used to verify the signature an identifier and hash of the
"Signature policy" shall be part of the signed data. Additional
information about the explicit policy (e.g. web reference to the
document) may be carried as "qualifiers" to the signature policy
identifier.
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When the signature policy not explicitly identified, but is implied by
the semantics of the data being signed, then the signature will include
a signature policy identifier that indicates that the signature policy
is implied. In this case the verification rules must be determined by
using other external data which will designate the signature policy to
be used. If it may be determined from the context that all the
documents to be verified refer to the same signature policy, then that
policy may be predetermined or fixed within the application.
In order to identify unambiguously the "Signature Validation Policy"
to be used to verify the signature an identifier and hash of the
"Signature policy" must be part of the signed data. Additional
information about the policy (e.g. web reference to the document) may
be carried as "qualifiers" to the signature policy identifier.
B.3.2 Commitment Type Indication
The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a signature policy, at a given time,
by a signer under an identifier, e.g. a name or a pseudonym, and
optionally a role".
The commitment type can be indicated in the electronic signature
either:
* explicitly using a "commitment type indication" in the
electronic signature;
* implicitly or explicitly from the semantics of the signed data.
If the indicated commitment type is explicit using a "commitment type
indication" in the electronic signature, acceptance of a verified
signature implies acceptance of the semantics of that commitment type.
The semantics of explicit commitment types indications must be
specified either as part of the signature policy or may be registered
for generic use across multiple policies.
If a signature includes a commitment type indication other than one of
those recognized under the signature policy the signature must be
treated as invalid.
How commitment is indicated using the semantics of the data being
signed is outside the scope of this document.
NOTE: Examples of commitment indicated through the semantics of the
data being signed, are:
* An explicit commitment made by the signer indicated by the type
of data being signed over. Thus, the data structure being
signed can have an explicit commitment within the context of
the application (e.g. EDIFACT purchase order).
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* An implicit commitment which is a commitment made by the signer
because the data being signed over has specific semantics
(meaning) which is only interpretable by humans, (i.e. free
text).
B.3.3 Certificate Identifier from the Signer
The definition of the ETSI electronic signature includes: "a
commitment has been explicitly endorsed under a signature policy,
at a given time, by a signer under an identifier, e.g. a name or a
pseudonym, and optionally a role."
In many real life environments users will be able to get from
different CAs or even from the same CA, different certificates
containing the same public key for different names. The prime
advantage is that a user can use the same private key for different
purposes. Multiple use of the private key is an advantage when a smart
card is used to protect the private key, since the storage of a smart
card is always limited. When several CAs are involved, each different
certificate may contain a different identity, e.g. as a national or as
an employee from a company. Thus when a private key is used for
various purposes, the certificate is needed to clarify the context in
which the private key was used when generating the signature. Where
there is the possibility of multiple use of private keys it is
necessary for the signer to indicate to the verifier the precise
certificate to be used.
Many current schemes simply add the certificate after the signed data
and thus are subject to various substitution attacks. An example of a
substitution attack is a "bad" CA that would issue a certificate to
someone with the public key of someone else. If the certificate from
the signer was simply appended to the signature and thus not protected
by the signature, any one could substitute one certificate by another
and the message would appear to be signed by some one else.
In order to counter this kind of attack, the identifier of the signer
has to be protected by the digital signature from the signer.
Although it does not provide the same advantages as the previous
technique, another technique to counter that threat has been
identified. It requires all CAs to perform a Proof Of Possession of
the private key at the time of registration. The problem with that
technique is that it does not provide any guarantee at the time of
verification and only some proof "after the event" may be obtained, if
and only if the CA keeps the Proof Of Possession in audit trail.
In order to identify unambiguously the certificate to be used for the
verification of the signature an identifier of the certificate from
the signer must be part of the signed data.
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B.3.4 Role Attributes
The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a non repudiation security policy,
at a given time, by a signer under an identifier, e.g. a name or a
pseudonym, and optionally a role. "
While the name of the signer is important, the position of the signer
within a company or an organization can be even more important. Some
contracts may only be valid if signed by a user in a particular role,
e.g. a Sales Director. In many cases whom the sales Director really
is, is not that important but being sure that the signer is empowered
by his company to be the Sales Director is fundamental.
This document defines two different ways for providing this feature:
* by placing a claimed role name in the CMS signed
attributes field;
* by placing a attribute certificate containing a certified
role name in the CMS signed attributes field.
NOTE: Another possible approach would have been to use additional
attributes containing the roles name(s) in the signer's certificate.
However, it was decided not to follow this approach as it breaks the
basic philosophy of the certificate being issued for one primary
purpose. Also, by using separate certificates for management of the
signer's identity certificate and management of additional roles can
simplify the management, as new identity keys need not be issued if a
use of role is to be changed.
B.3.5.1 Claimed Role
The signer may be trusted to state his own role without any
certificate to corroborate this claim. In which case the claimed role
can be added to the signature as a signed attribute.
B.3.5.2 Certified Role
Unlike public key certificates that bind an identifier to a public
key, Attribute Certificates bind the identifier of a certificate to
some attributes, like a role. An Attribute Certificate is NOT issued
by a CA but by an Attribute Authority (AA). The Attribute Authority
will be most of the time under the control of an organization or a
company that is best placed to know which attributes are relevant for
which individual.
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The Attribute Authority may use or point to public key certificates
issued by any CA, provided that the appropriate trust may be placed
in that CA. Attribute Certificates may have various periods of
validity. That period may be quite short, e.g. one day. While this
requires that a new Attribute Certificate is obtained every day, valid
for that day, this can be advantageous since revocation of such
certificates may not be needed. When signing, the signer will have to
specify which Attribute Certificate it selects. In order to do
so, a reference to the Attribute Certificate will have to be included
in the signed data in order to be protected by the digital signature
from the signer.
In order to identify unambiguously the attribute certificate(s) to be
used for the verification of the signature an identifier of the
attribute certificate(s) from the signer must be part of the signed
data.
B.3.5 Signer Location
In some transactions the purported location of the signer at the time
he or she applies his signature may need to be indicated. For this
reason an optional location indicator must be able to be included.
In order to provide indication of the location of the signer at the
time he or she applied his signature a location attribute may be
included in the signature.
B.3.6 Signing Time
The definition of electronic signature includes: "a commitment has
been explicitly endorsed under a signature policy, at a given time,
by a signer under an identifier, e.g. a name or a pseudonym, and
optionally a
role. "
There are several ways to address this problem. The solution adopted
in this document is to sign over a time which the signer claims is the
signing time (i.e. claimed signing time) and to require a trusted
time stamp to be obtained when building a ES with Timestamp. When a
verifier accepts a signature, the two times must be within acceptable
limits.
The solution that is adopted in this document offers the major
advantage that electronic signatures can be generated without any on-
line connection to a trusted time source (i.e. they may be generated
off-line).
Thus two dates and two signatures are required:
* a signing time indicated by the signer and which is part of
the data signed by the signer (i.e. part of the basic
electronic signature);
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* a time indicated by a TimeStamping Authority (TSA) which is
signed over the digital signature value of the basic electronic
signature. The signer, verifier or both may obtain the TSA
timestamp.
In order for an electronic signature to be valid under a signature
policy, it must be timestamped by a TSA where the signing time as
indicated by the signer and the time of time stamping as indicated by
a TSA must be "close enough" to meet the requirements of the signature
validation policy.
"Close enough" means a few minutes, hours or even days according to
the "Signature Validation Policy".
NOTE: The need for Timestamping is further explained in section B.4.5.
A further optional attribute is defined in this document to timestamp
the content, to provide proof of the existence of the content, at the
time indicated by the timestamp.
Using this optional attribute a trusted secure time may be obtained
before the document is signed and included under the digital signature.
This solution requires an on-line connection to a trusted timestamping
service before generating the signature and may not represent the
precise signing time, since it can be obtained in advance. However,
this optional attribute may be used by the signer to prove that the
signed object existed before the date included in the timestamp (see
3.12.3, Content Timestamp).
Also, the signing time should be between the time indicated by this
timestamp and time indicated by the ES-T timestamp.
B.3.7 Content Format
When presenting signed data to a human user it may be important that
there is no ambiguity as to the presentation of the signed information
to the relying party. In order for the appropriate representation
(text, sound or video) to be selected by the relying party a content
hint may be indicated by the signer. If a relying party system does not
use the format specified in the content hints to present the data to
the relying party, the electronic signature may not be valid.
B.4 Components of Validation Data
B.4.1 Revocation Status Information
A verifier will have to prove that the certificate of the signer was
valid at the time of the signature. This can be done by either:
* using Certificate Revocation Lists (CRLs);
* using responses from an on-line certificate status server
(for example; obtained through the OCSP protocol).
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B.4.2 CRL Information
When using CRLs to get revocation information, a verifier will have to
make sure that he or she gets at the time of the first verification the
appropriate certificate revocation information from the signer's CA.
This should be done as soon as possible to minimize the time delay
between the generation and verification of the signature. This involves
checking that the signer certificate serial number is not included in
the CRL. The signer, the verifier or any other third party may obtain
either this CRL. If obtained by the signer, then it must be conveyed
to the verifier. It may be convenient to archive the CRL for ease of
subsequent verification or arbitration.
Alternatively, provided the CRL is archived elsewhere which is
accessible for the purpose of arbitration, then the serial number of
the CRL used may be archived together with the verified electronic
signature.
It may happen that the certificate serial number appears in the CRL
but with the status "suspended" (i.e. on hold). In such a case, the
electronic signature is not yet valid, since it is not possible to
know whether the certificate will or will not be revoked at the end
of the suspension period. If a decision has to be taken immediately
then the signature has to be considered as invalid. If a decision can
wait until the end of the suspension period, then two cases are
possible:
* the certificate serial number has disappeared from the list
and thus the certificate can be considered as valid and that
CRL must be captured and archived either by the verifier or
elsewhere and be kept accessible for the purpose of arbitration.
* the certificate serial number has been maintained on the list
with the status definitively revoked and thus the electronic
signature must be considered as invalid and discarded.
At this point the verifier may be convinced that he or she got a valid
signature, but is not yet in a position to prove at a later time that
the signature was verified as valid. Before addressing this point, an
alternative to CRL is to use OCSP responses.
ETSI TC-SEC, Pinkas, Ross, Pope Informational RFC [Page 71]
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B.4.3 OCSP Information
When using OCSP to get revocation information , a verifier will have
to make sure that he or she gets at the time of the first verification
an OCSP response that contains the status "valid". This should be done
as soon as possible after the generation of the signature. The signer,
the verifier or any other third party may fetch this OCSP response.
Since OSCP responses are transient and thus are not archived by any
TSP including CA, it is the responsibility of every verifier to make
sure that it is stored in a safe place. The simplest way is to store
them associated with the electronic signature. An alternative would be
to store them in some storage so that they can then be easily
retrieved.
In the same way as for the case of the CRL, it may happen that the
certificate is declared as invalid but with the secondary status
"suspended".
In such a case, the electronic signature is not yet valid, since it is
not possible to know whether the certificate will or will not be
revoked at the end of the suspension period. If a decision has to be
taken immediately then the electronic signature has to be considered
as invalid. If a decision can wait until the end of the suspension
period, then two cases are possible:
* An OCSP response with a valid status is obtained at a later
date and thus the certificate can be considered as valid and
that OCSP response must be captured.
* An OCSP response with an invalid status is obtained with a
secondary status indicating that the certificate is
definitively revoked and thus the electronic signature must be
considered as invalid and discarded.
As in the CRL case, at this point, the verifier may be convinced that
he or she got a valid signature, but is not yet in a position to prove
at a later time that the signature was verified as valid.
B.4.4 Certification Path
A verifier will have to prove that the certification path was valid,
at the time of the signature, up to a trust point according to the
naming constraints and the certificate policy constraints from the
"Signature Validation Policy". It will be necessary to capture all the
certificates from the certification path, starting with those from the
signer and ending up with those of the self-signed certificate from
one trusted root of the "Signature Validation Policy". In addition, it
will be necessary to capture the Authority Revocation Lists (ARLs) to
prove than none of the CAs from the chain was revoked at the time of
the signature.
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As in the OCSP case, at this point, the verifier may be convinced that
he or she got a valid signature, but is not yet in a position to prove
at a later time that the signature was verified as valid.
B.4.5 Timestamping for Long Life of Signature
An important property for long standing signatures is that a
signature, having been found once to be valid, must continue to be so
months or years later.
A signer, verifier or both may be required to provide on request,
proof that a digital signature was created or verified during the
validity period of the all the certificates that make up the
certificate path. In this case, the signer, verifier or both will
also be required to provide proof that all the user and CA
certificates used were not revoked when the signature was created
or verified.
It would be quite unacceptable, to consider a signature as invalid
even if the keys or certificates were later compromised. Thus there
is a need to be able to demonstrate that the signature keys was valid
around the time that the signature was created to provide long term
evidence of the validity of a signature.
It could be the case that a certificate was valid at the time of the
signature but revoked some time later. In this event, evidence must be
provided that the document was signed before the signing key was
revoked.
Timestamping by a Time Stamping Authority (TSA) can provide such
evidence. A time stamp is obtained by sending the hash value of the
given data to the TSA. The returned "timestamp" is a signed document
that contains the hash value, the identity of the TSA, and the time of
stamping. This proves that the given data existed before the time of
stamping. Timestamping a digital signature (by sending a hash of the
signature to the TSA) before the revocation of the signer's private
key, provides evidence that the signature has been created before the
key was revoked.
If a recipient wants to hold a valid electronic signature he will have
to ensure that he has obtained a valid time stamp for it, before that
key (and any key involved in the validation) is revoked. The sooner
the timestamp is obtained after the signing time, the better.
It is important to note that signatures may be generated "off-line"
and time-stamped at a later time by anyone, for example by the signer
or any recipient interested in the value of the signature. The time
stamp can thus be provided by the signer together with the signed
document, or obtained by the recipient following receipt of the signed
document.
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The time stamp is NOT a component of the Electronic Signature, but the
essential component of the ES with Timestamp.
It is required in this document that signer's digital signature value
is timestamped by a trusted source, known as a TimeStamping Authority.
This document requires that the signer's digital signature value is
timestamped by a trusted source before the electronic signature can
become a ES with Complete validation data (ES-C). The acceptable TSAs
are specified in the Signature Validation Policy.
Should both the signer and verifier be required to timestamp the
signature value to meet the requirements of the signature policy, the
signature policy MAY specify a permitted time delay between the two
time stamps.
B.4.6 Timestamping before CA Key Compromises
Timestamped extended electronic signatures are needed when there is a
requirement to safeguard against the possibility of a CA key in the
certificate chain ever being compromised. A verifier may be required
to provide on request, proof that the certification path and the
revocation information used a the time of the signature were valid,
even in the case where one of the issuing keys or OCSP responder keys
is later compromised.
The current document defines two ways of using timestamps to protect
against this compromise:
* Timestamp the ES with Complete validation data, when an OCSP
response is used to get the status of the certificate from the
signer.
* Timestamp only the certification path and revocation information
references when a CRL is used to get the status of the
certificate from the signer.
NOTE: the signer, verifier or both may obtain the timestamp.
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B.4.6.1 Timestamping the ES with Complete validation data
When an OCSP response is used, it is necessary to time stamp in
particular that response in the case the key from the responder would
be compromised. Since the information contained in the OCSP response
is user specific and time specific, an individual time stamp is needed
for every signature received. Instead of placing the time stamp only
over the certification path references and the revocation information
references, which include the OCSP response, the time stamp is placed
on the ES-C. Since the certification path and revocation information
references are included in the ES with Complete validation data they
are also protected. For the same cryptographic price, this provides an
integrity mechanism over the ES with Complete validation data. Any
modification can be immediately detected. It should be noticed that
other means of protecting/detecting the integrity of the ES with
Complete Validation Data exist and could be used.
Although the technique requires a time stamp for every signature, it
is well suited for individual users wishing to have an integrity
protected copy of all the validated signatures they have received.
By timestamping the complete electronic signature, including the
digital signature as well as the references to the certificates and
revocation status information used to support validation of that
signature, the timestamp ensures that there is no ambiguity in the
means of validating that signature.
This technique is referred to as ES with eXtended validation data
(ES-X), type 1 Timestamped in this document.
NOTE: Trust is achieved in the references by including a hash of the
data being referenced.
If it is desired for any reason to keep a copy of the additional data
being referenced, the additional data may be attached to the
electronic signature, in which case the electronic signature becomes
a ES-X Long as defined by this document.
A ES-X Long Timestamped is simply the concatenation of a ES-X
Timestamped with a copy of the additional data being referenced.
B.4.6.2 Timestamping Certificates and Revocation Information
References Timestamping each ES with Complete validation data as
defined above may not be efficient, particularly when the same set of
CA certificates and CRL information is used to validate many
signatures.
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Timestamping CA certificates will stop any attacker from issuing bogus
CA certificates that could be claimed to existing before the CA key
was compromised. Any bogus timestamped CA certificates will show that
the certificate was created after the legitimate CA key was
compromised. In the same way, timestamping CA CRLs, will stop any
attacker from issuing bogus CA CRLs which could be claimed to existing
before the CA key was compromised.
Timestamping of commonly used certificates and CRLs can be done
centrally, e.g. inside a company or by a service provider. This method
reduces the amount of data the verifier has to timestamp, for example
it could reduce to just one time stamp per day (i.e. in the case were
all the signers use the same CA and the CRL applies for the whole day).
The information that needs to be time stamped is not the actual
certificates and CRLs but the unambiguous references to those
certificates and CRLs.
To comply with extended validation data, type 2 Timestamped, this
document requires the following:
* All the CA certificates references and revocation information
references (i.e. CRLs) used in validating the ES-C are covered
by one or more timestamp.
Thus a ES-C with a timestamp signature value at time T1, can be proved
valid if all the CA and CRL references are timestamped at time T1+.
B.4.7 Timestamping for Long Life of Signature
Advances in computing increase the probability of being able to break
algorithms and compromise keys. There is therefore a requirement to be
able to protect electronic signatures against this probability.
Over a period of time weaknesses may occur in the cryptographic
algorithms used to create an electronic signature (e.g. due to the
time available for cryptoanalysis, or improvements in cryptoanalytical
techniques). Before this such weaknesses become likely, a verifier
should take extra measures to maintain the validity of the electronic
signature. Several techniques could be used to achieve this goal
depending on the nature of the weakened cryptography. In order to
simplify, a single technique, called Archive validation data, covering
all the cases is being used in this document.
Archive validation data consists of the Complete validation data and
the complete certificate and revocation data, time stamped together
with the electronic signature. The Archive validation data is
necessary if the hash function and the crypto algorithms that were
used to create the signature are no longer secure. Also, if it cannot
be assumed that the hash function used by the Time Stamping Authority
is secure, then nested timestamps of Archived Electronic Signature are
required.
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Internet Draft Electronic Signature Formats
The potential for Trusted Service Provider (TSP) key compromise should
be significantly lower than user keys, because TSP(s) are expected to
use stronger cryptography and better key protection. It can be expected
that new algorithms (or old ones with greater key lengths) will be
used. In such a case, a sequence of timestamps will protect against
forgery. Each timestamp needs to be affixed before either the
compromise of the signing key or of the cracking of the algorithms used
by the TSA. TSAs (TimeStamping Authorities) should have long keys (e.g.
which at the time of drafting this document was 2048 bits for the
signing RSA algorithm) and/or a "good" or different algorithm.
Nested timestamps will also protect the verifier against key compromise
or cracking the algorithm on the old electronic signatures.
The process will need to be performed and iterated before the
cryptographic algorithms used for generating the previous time stamp
are no longer secure. Archive validation data may thus bear multiple
embedded time stamps.
B.4.8 Reference to Additional Data
Using type 1 or 2 of Timestamped extended validation data verifiers
still needs to keep track of all the components that were used to
validate the signature, in order to be able to retrieve them again
later on. These components may be archived by an external source like
a trusted service provider, in which case referenced information that
is provided as part of the ES with Complete validation data (ES-C) is
adequate. The actual certificates and CRL information reference in the
ES-C can be gathered when needed for arbitration.
B.4.9 Timestamping for Mutual Recognition
In some business scenarios both the signer and the verifier need to
timestamp their own copy of the signature value. Ideally the two
timestamps should be as close as possible to each other.
Example: A contract is signed by two parties A and B representing
their respective organizations, to timestamp the signer and verifier
data two approaches are possible:
* under the terms of the contract pre-defined common "trusted"
TSA may be used;
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* if both organizations run their own timestamping services, A
and B can have the transaction timestamped by these two
timestamping services. In the latter case, the electronic
signature will only be considered as valid, if both timestamps
were obtained in due time (i.e. there should not be a long
delay between obtaining the two timestamps). Thus, neither A
nor B can repudiate the signing time indicated by their own
timestamping service.
Therefore, A and B do not need to agree on a common "trusted" TSA to
get a valid transaction.
It is important to note that signatures may be generated "off-line"
and timestamped at a later time by anyone, e.g. by the signer or any
recipient interested in validating the signature. The timestamp over
the signature from the signer can thus be provided by the signer
together with the signed document, and /or obtained by the verifier
following receipt of the signed document.
The business scenarios may thus dictate that one or more of the long-
term signature timestamping methods describe above be used. This will
need to be part of a mutually agreed the Signature Validation Policy
with is part of the overall signature policy under which digital
signature may be used to support the business relationship between the
two parties.
B.4.10 TSA Key Compromise
TSA servers should be built in such a way that once the private
signature key is installed, that there is minimal likelihood of
compromise over as long as possible period. Thus the validity period
for the TSA's keys should be as long as possible.
Both the ES-T and the ES-C contain at least one time stamp over the
signer's signature. In order to protect against the compromise of the
private signature key used to produce that timestamp, the Archive
validation data can be used when a different TimeStamping Authority key
is involved to produce the additional timestamp. If it is believed that
the TSA key used in providing an earlier timestamp may ever be
compromised (e.g. outside its validity period), then the ES-A should be
used. For extremely long periods this may be applied repeatedly using
new TSA keys.
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B.5 Multiple Signatures
Some electronic signatures may only be valid if they bear more than one
signature. This is the case generally when a contract is signed between
two parties. The ordering of the signatures may or may not be
important, i.e. one may or may not need to be applied before the other.
Several forms of multiple and counter signatures may need to be
supported, which fall into two basic categories:
* independent signatures;
* embedded signatures.
Independent signatures are parallel signatures where the ordering of
the signatures is not important. The capability to have more than one
independent signature over the same data must be provided.
Embedded signatures are applied one after the other and are used where
the order the signatures are applied is important. The capability to
sign over signed data must be provided.
These forms are described in section 3.13. All other multiple signature
schemes, e.g. a signed document with a countersignature, double
countersignatures or multiple signatures, can be reduced to one or more
occurrence of the above two cases.
Annex C (informative): Identifiers and roles
C.1 Signer Name Forms
The name used by the signer, held as the subject in the signer's
certificate, must uniquely identify the entity. The name must be
allocated and verified on registration with the Certification
Authority, either directly or indirectly through a Registration
Authority, before being issued with a Certificate.
This document places no restrictions on the form of the name. The
subject's name may be a distinguished name, as defined in [RFC2459],
held in the subject field of the certificate, or any other name form
held in the X.509 subjectAltName certificate extension field. In the
case that the subject has no distinguished name, the subject name can
be an empty sequence and the subjectAltName extension must be critical.
C.2 TSP Name Forms
All TSP name forms (Certification Authorities, Attribute Authorities
and TimeStamping Authorities) must be in the form of a distinguished
name held in the subject field of the certificate.
The TSP name form must include the legal jurisdiction (i.e. country)
under which it operates and an identification for the organization
providing the service.
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C.3 Roles and Signer Attributes
Where a signer signs as an individual but wishes to also identify
him/herself as acting on behalf of an organization, it may be necessary
to provide two independent forms of identification. The first identity,
with is directly associated with the signing key identifies him/her as
an individual. The second, which is managed independently, identifies
that person acting as part of the organization, possibly with a given
role.
In this case the first identity is carried in the
subject/subjectAltName field of the signer's certificate as described
above.
This document supports the following means of providing a second form
of identification:
* by placing a secondary name field containing a claimed role in
the CMS signed attributes field;
* by placing an attribute certificate containing a certified role
in the CMS signed attributes field.
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