Network Working Group T. Looker
Internet-Draft MATTR
Intended status: Informational P. Bastian
Expires: 21 December 2023 19 June 2023
JWT and CWT Status List
draft-looker-oauth-jwt-cwt-status-list-00
Abstract
This specification defines a status list representation and
processing rules for usage with JSON Web Tokens [RFC7519] and CBOR
Web Tokens [RFC8392].
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://vcstuff.github.io/draft-looker-oauth-jwt-cwt-status-list/
draft-looker-oauth-jwt-cwt-status-list.html. Status information for
this document may be found at https://datatracker.ietf.org/doc/draft-
looker-oauth-jwt-cwt-status-list/.
Source for this draft and an issue tracker can be found at
https://github.com/vcstuff/draft-looker-oauth-jwt-cwt-status-list.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. JSON Web Token Representation . . . . . . . . . . . . . . . . 4
4.1. Referenced Token Format and Processing Requirements . . . 4
4.1.1. Status Claim Format . . . . . . . . . . . . . . . . . 5
4.2. Status List JWT Format and Processing Requirements . . . 5
4.2.1. Status List Claim Format . . . . . . . . . . . . . . 7
4.2.2. Status List Encoding . . . . . . . . . . . . . . . . 7
5. Status Types . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Status Types Values . . . . . . . . . . . . . . . . . . . 10
5.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Extended Status List Types . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. Correct decoding and parsing of the encoded status
list . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Cached and Stale status lists . . . . . . . . . . . . . . 10
6.3. Authorized access to the Status List . . . . . . . . . . 10
6.4. History . . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
7.1. Herd Privacy . . . . . . . . . . . . . . . . . . . . . . 11
7.2. Profiling . . . . . . . . . . . . . . . . . . . . . . . . 11
7.3. Correlation Risks and Tracking . . . . . . . . . . . . . 11
7.4. Malicious Issuers . . . . . . . . . . . . . . . . . . . . 11
7.5. Hosting Service (what's a better name here?) . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Normative References . . . . . . . . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
Document History . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
JSON Web Tokens (JWTs) [RFC7519] and CBOR Web Tokens (CWTs) [RFC8392]
as secure token formats, have vast possible applications. Some of
these applications can involve issuing a token whereby certain
semantics about the token can change over time which are important to
be able to communicate to relying parties in an interoperable manner,
such as whether the token is considered invalidated or suspended by
its issuer.
This document defines a Status List in JWT and CWT representations
that describes the individual statuses of multiple Referenced Tokens.
The statuses of all Referenced Tokens are conveyed via a bit array in
the Status List. Each Referenced Token is allocated an index during
issuance which represents a position within this bit array and the
value of the bit(s) at this position correspond to the Referenced
Token's status. The document also defines how an issuer of a
Referenced Token in JWT or CWT representation references a Status
List Token. Status Lists may be composed for expressing a range of
Status Types, the document defines basic Status Types for the most
common use cases as well as an extensibility mechanism for custom
Status Types. The Status List Token may be used by an issuer in the
Issuer-Holder-Verifier model, as described in (XXX) to express the
status of verifiable credentials (Referenced Tokens) issued by an
issuer.
The following diagram depicts the basic conceptual relationship.
+------------------+ +-------------------+
| | References | |
| |------------------->| |
| Referenced Token | | Status List Token |
| (JWT/CWT Based) | | (JWT/CWT Based) |
| | Describes Status | |
| |<-------------------| |
+------------------+ +-------------------+
1.1. Rationale
Revocation mechanisms are an essential part for most identity
ecosystems. In the past, revocation of X.509 TLS certificates has
been proven difficult as traditional certificate revocation lists
(CRLs) have limited scalability and the Online Certificate Status
Protocol (OCSP) has additional privacy risks as the client is leaking
the requested website to a third party. OCSP stapling is addressing
some of these problems at the cost of less up-to-date data. Modern
approaches use accumulator-based revocation registries and Zero-
Knowledge-Proofs to accommodate for this privacy gap but face
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scalability issues again.
The approach of this specification seeks to find a balance between
scalability, security and privacy by minimizing the status
information to mere bits and compressing the resulting binary data.
Thereby a Status List may contain statuses of 100.000 or more
Referenced Tokens, but still remain relatively small. Placing large
amounts of Referenced Tokens into the same list also enables a herd
privacy towards the Issuer.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
Status List A bit array that lists the statuses of many Referenced
Tokens.
Status List Token A token in JWT or CWT representation that contains
a Status List.
Referenced Token A token in JWT or CWT representation which contains
a reference to a Status List Token. The information from the
contained Status List may give a verifier additional information
about up-to-date status of the Referenced Token.
4. JSON Web Token Representation
4.1. Referenced Token Format and Processing Requirements
The following rules apply to validating a Referenced Token in JWT
representation which references a Status List Token. Application of
additional restrictions and policy are at the discretion of the
verifying party.
1. The JWT MUST contain an "iss" (issuer) claim that contains a
unique string based identifier for the entity that issued the
JWT. In the absence of an application profile specifying
otherwise, compliant applications MUST compare issuer values
using the Simple String Comparison method defined in
Section 6.2.1 of [RFC3986]. The value MUST be equal to that of
the "iss" claim contained within the referenced Status List
Token.
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2. The JWT MUST contain an "status" (status) claim conforming to the
rules outlined in Section 4.1.1
The following example is the decoded header and payload of a JWT
meeting the processing rules as defined above.
{
"alg": "ES256",
"kid": "11"
}
.
{
"iss": "https://example.com",
"status": {
"bits": 1,
"idx": 0,
"uri": "https://example.com/statuslists/1"
}
}
4.1.1. Status Claim Format
The following rules apply to validating the "status" (status) claim
1. The claim value MUST be a valid JSON object.
2. The claim value object MUST contain an "idx" (index) attribute
with a numeric based value that represents the index to check for
status information in the Status List for the current JWT. The
value of this attribute MUST be a non-negative number, containing
a value of zero or greater. Refer to xx for details on the
validation procedure.
3. The claim value object MUST contain a "uri" attribute with a
string based value that identifies the Status List containing the
status information for the JWT. The value of this attribute MUST
be a uri conforming to [RFC3986]
4.2. Status List JWT Format and Processing Requirements
The following rules apply to validating a JWT based Status List
Token. Application of additional restrictions and policy are at the
discretion of the verifying party.
1. The JWT MUST contain an "iss" (issuer) claim that contains a
unique string based identifier for the entity that issued the
JWT. In the absence of an application profile specifying
otherwise, compliant applications MUST compare issuer values
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using the Simple String Comparison method defined in
Section 6.2.1 of [RFC3986]. The value MUST be equal to that of
the "iss" claim contained within the Referenced Token.
2. The JWT MUST contain a "sub" (subject) claim that contains an
unique string based identifier for that Referenced Token. The
value MUST be equal to that of the "uri" claim contained in the
"status" claim of the Referenced Token.
3. The JWT MUST contain an "iat" (issued at) claim that identifies
the time at which it was issued.
4. The JWT MUST contain an "status_list" (status list) claim
conforming to the rules outlined in Section 4.2.1.
5. The JWT MAY contain an "exp" (expiration time) claim that
convey's when it is considered expired by its issuer.
6. The JWT MAY contain other claims.
7. The JWT MUST be digitally signed using an asymmetric
cryptographic algorithm. Relying parties MUST reject the JWT if
it is using a Message Authentication Code (MAC) based algorithm.
Relying parties MUST reject JWTs with an invalid signature.
8. Relying parties MUST reject a JWT that is not valid in all other
respects per "JSON Web Token (JWT)" [RFC7519].
{
"typ": "statuslist+jwt",
"alg": "ES256",
"kid": "11"
}
.
{
"iss": "https://example.com",
"sub": "https://example.com/statuslists/1",
"iat": 1683560915,
"exp": 1686232115,
"status_list": {
"bits": 1,
"lst": "H4sIAMo_jGQC_zvp..MAZLRLMQMAAAA"
}
}
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4.2.1. Status List Claim Format
The following rules apply to validating the "status_list" (status
list) claim
1. The claim value MUST be a valid JSON object.
2. The claim value object MUST contain a "bits" (bit size) attribute
with an numeric based value that represents the number of bits
per Referenced Token in the Status List ("lst") of the Status
List JWT. The allowed values for "bits" are 1,2,4 and 8.
3. The claim value object MUST contain a "lst" (list) attribute with
a string based value that represents the status values for all
the tokens it conveys statuses for. The value MUST be computed
using the algorithm described in Section 4.2.2.
4.2.2. Status List Encoding
Each status of a Referenced Token MUST be represented with a bit size
of 1,2,4, or 8. Therefore up to 2,4,16, or 256 statuses for a
Referenced Token, depending on the bit-size, are possible. This
limitation is intended to limit bit manipulation necessary to a
single byte for every operation and thus keeping implementations
simpler and less error prone.
1. The overall Status List is encoded as a byte array. Depending on
the "bit-size" each byte corresponds to 8/(#bit-size) statuses
(8,4,2, or 1). The status of each Referenced Token is identified
using the "index" that maps to one or more specific bits within
the byte array. The index starts counting at 0 and ends with
"size" - 1(being the last valid entry). The bits within an array
are counted from least significant bit "0" to the most
significant bit ("7"). All bits of the byte array at a
particular index are set to a status value.
2. The complete byte array is compressed using gZIP [RFC1952].
3. The result of the gZIP compression is then encoded as URL-safe
base64 encoding without padding encoding as defined in Section 2
of [RFC7515] and stored as a string.
Example of a Status List representing the statuses of 16 Referenced
Tokens (1-bit status type) with indices 0 to 15 (2 bytes):
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status[0] = 1
status[1] = 0
status[2] = 0
status[3] = 1
status[4] = 1
status[5] = 1
status[6] = 0
status[7] = 1
status[8] = 1
status[9] = 1
status[10] = 0
status[11] = 0
status[12] = 0
status[13] = 1
status[14] = 0
status[15] = 1
These bits are concatenated:
byte 0 1 2
bit 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+...
values |1|0|1|1|1|0|0|1| |1|0|1|0|0|0|1|1| |0|...
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+...
index 7 6 5 4 3 2 1 0 15 ... 10 9 8 23
\_______________/ \_______________/
0xB9 0xA3
Resulting in the byte array:
byte_array = [0xB9, 0xA3]
After compression and Base64URL encoding the generated Status List
is:
"status_list": {
"bits": 1,
"lst": "H4sIAMo_jGQC_9u5GABc9QE7AgAAAA"
}
Example of a more complex status list of length 12 using 2 bit
statuses (3 bytes):
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status[0] = 1
status[1] = 2
status[2] = 0
status[3] = 3
status[4] = 0
status[5] = 1
status[6] = 0
status[7] = 1
status[8] = 1
status[9] = 2
status[10] = 3
status[11] = 3
These bits are concatenated:
byte 0 1 2
bit 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
values |1|1|0|0|1|0|0|1| |0|1|0|0|0|1|0|0| |1|1|1|1|1|0|0|1|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
\ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ /
status 3 0 2 1 1 0 1 0 3 3 2 1
index 3 2 1 0 7 6 5 4 11 10 9 8
\___________/ \___________/ \___________/
0xC9 0x44 0xF9
Resulting in the byte array:
byte_array = [0xC9, 0x44, 0xF9]
After compression and Base64URL encoding the generated Status List
is:
"status_list": {
"bits": 2,
"lst": "H4sIAMo_jGQC_zvp8hMAZLRLMQMAAAA"
}
5. Status Types
This document defines the possible statuses of Referenced Tokens as
Status Type values. If the Status List contains more than one bit
per token (as defined by "bits" in the Status List) then the whole
value of bits MUST describe one value. A Status List can not
encompass multiple statuses per individual bits for a Reference
Token.
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The registry in this document describes the basic Status Type values
required for the most common use cases. The registry may be extended
as describes in XXX.
5.1. Status Types Values
A status describes the state, mode, condition or stage of an entity
that is described by the status list. Status Types MUST be numeric
based values between 0 and 255. Status types described by this
specification comprise: 0x00 - "VALID" - The status of the Token is
valid, correct or legal. 0x01 - "INVALID" - The status of the Token
is revoked, annulled, taken back, recalled or cancelled. This state
is irreversible. 0x02 - "SUSPENDED" - The status of the Token is
temporarily invalid, hanging, debarred from privilege. This state is
reversible.
The issuer of the Status List Token MUST choose an adequate "bits"
(bit size) to be able to describe the required Status Types.ST be
used for the "typ" attribute within the "status_list".
5.1.1. Examples
In the first example the Status List shall be used as a revocation
list. It only requires the Status Types "VALID" and "INVALID",
therefore a "bits" of 1 is sufficient.
In the second example the Status List shall additionally include the
Status Type "SUSPENDED. As the Status Type value for "SUSPENDED" is
0x02 and doe snot fit into 1 bit, the "bits" is required to be 2.
5.2. Extended Status List Types
6. Security Considerations
6.1. Correct decoding and parsing of the encoded status list
TODO elaborate on risks of incorrect parsing/decoding leading to
erroneous status data
6.2. Cached and Stale status lists
TODO consumers/Verifiers of the status list should be aware if they
fetch the up-to-date data
6.3. Authorized access to the Status List
TODO elaborate on authorization mechanisms preventing misuse and
profiling as described in privacy section
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6.4. History
TODO elaborate on status list only providing the up-to date/latest
status, no historical data, may be provided by the underlying hosting
architecture
7. Privacy Considerations
7.1. Herd Privacy
TODO elaborate on herd privacy, size of the status list
7.2. Profiling
TODO elaborate on Verifiers regularly fetching the status list to
create a profile, possible countermeasures with authorized access to
the status list
7.3. Correlation Risks and Tracking
TODO elaborate on Issuer-Verifier correlation and Verifier-Verifier
correlation as the status list introduces unique,trackable data TODO
elaborate on issuers avoiding sequential usage of indices and status
lists TODO elaborate that a status list only gives information about
the maximum number of possible statuses that a list conveys, issuers
are recommended to pre-allocate lists, use dead entries that are
never assigned or other obfuscation mechanisms
7.4. Malicious Issuers
TODO elaborate on issuers generating unique status lists per
Referenced Token that do not offer herd privacy
7.5. Hosting Service (what's a better name here?)
TODO elaborate on increased privacy if the status list is hosted by a
third party instead of the issuer reducing tracking possiblities TODO
evaluate deifnition of Status List Provider? An entity that hosts
the Status List as a resource for potential verifiers. The Status
List Provider may be the issuer of the Status List but may also be
outsourced to a trusted third party.
8. IANA Considerations
This document has no IANA actions.
9. Normative References
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[RFC1952] Deutsch, P., "GZIP file format specification version 4.3",
RFC 1952, DOI 10.17487/RFC1952, May 1996,
<https://www.rfc-editor.org/rfc/rfc1952>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/rfc/rfc7515>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/rfc/rfc7519>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
Acknowledgments
TODO acknowledge.
Document History
-00
* Initial draft
Authors' Addresses
Tobias Looker
MATTR
Email: tobias.looker@mattr.global
Paul Bastian
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Email: paul.bastian@posteo.de
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