Internet Draft Jesse Walker
Expiration: April 2002 Amol Kulkarni
File: draft-ietf-rap-cops-tls-02.txt Intel Corp.
COPS Over TLS
Last Updated: October 18, 2001
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC-2119].
Abstract
This memo describes how to use TLS to secure COPS connections over
the Internet.
Please send comments on this document to the rap@ops.ietf.org
mailing list.
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Table Of Contents
1. Introduction...................................................3
2. COPS Over TLS..................................................3
2.1. Connection Initiation........................................3
2.2. Connection Closure...........................................4
2.2.1. PEP System Behavior........................................4
2.2.2. PDP System Behavior........................................4
2.3. Port Number..................................................5
3. Endpoint Identification and Access Control.....................5
3.1. PDP Identity.................................................5
3.2. PEP Identity.................................................6
4. IANA Considerations............................................6
5. Security Considerations........................................6
6. Acknowledgements...............................................6
7. References.....................................................7
8. Author Addresses...............................................7
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1. Introduction
COPS [COPS] was designed to distribute clear-text policy information
from a centralized Policy Decision Point (PDP) to a set of Policy
Enforcement Points (PEP) in the Internet. COPS provides its own
security mechanisms to protect the per-hop integrity of the deployed
policy. However, the use of COPS for sensitive applications such as
some types of security policy distribution requires additional
security measures, such as data privacy. This is because some
organizations find it necessary to hide some or all of their security
policies, e.g., because policy distribution to devices such as mobile
platforms can cross domain boundaries.
TLS [TLS] was designed to provide channel-oriented security. TLS
standardizes SSL and may be used with any connection-oriented
service. TLS provides mechanisms for both one- and two-way
authentication, dynamic session keying, and data stream privacy and
integrity.
This document describes how to use COPS over TLS. "COPS over TLS" is
abbreviated COPS/TLS.
2. COPS Over TLS
COPS/TLS is very simple: use COPS over TLS exactly as you would use
COPS over TCP.
2.1. Connection Initiation
The system acting as the PEP also acts as the TLS client. This system
initiates a connection to the PDP to the secure COPS port. When this
succeeds, the PEP system sends the TLS ClientHello to begin the TLS
handshake. When the TLS handshake completes, the PEP MAY initiate the
first COPS message. All COPS data MUST be sent as TLS "application
data". Normal COPS behavior follows.
All PEP implementations of COPS/TLS MUST support an access control
mechanism to identify authorized PDPs. This requirement provides a
level of assurance that the policy arriving at the PEP is actually
valid. The access control mechanism implemented is outside the scope
of this document. PEP implementations SHOULD require the use of this
access control mechanism for operation of COPS over TLS. When access
control is enabled, the PEP implementation MUST NOT initiate COPS/TLS
connections to systems not authorized as PDPs by the access control
mechanism.
Similarly, PDP COPS/TLS implementations MUST support an access
control mechanism permitting them to restrict their services to
authorized PEP systems only. However, implementations MUST NOT
require the use of an access control mechanism at the PDP, as
organizations might not consider the types of policy being deployed
as sensitive, and therefore do not need to incur the expense of
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managing credentials for the PEP systems. If access controls are
used, however, the PDP implementation MUST terminate COPS/TLS
connections from unauthorized PEP systems and log an error if an
auditable logging mechanism is present.
2.2. Connection Closure
TLS provides facilities to securely close its connections. Reception
of a valid closure alert assures an implementation that no further
data will arrive on that connection. The TLS specification requires
TLS implementations to initiate a closure alert exchange before
closing a connection. It also permits TLS implementations to close
connections without waiting to receive closure alerts from the peer,
provided they send their own first. A connection closed in this way
is known as an "incomplete close". TLS allows implementations to
reuse the session in this case, but COPS/TLS makes no use of this
capability.
A connection closed without first sending a closure alert is known as
a "premature close". Note that a premature close does not call into
question the security of the data already received, but simply
indicates that subsequent data might have been truncated. Because TLS
is oblivious to COPS message boundaries, it is necessary to examine
the COPS data itself (specifically the Message header) to determine
whether truncation occurred.
2.2.1. PEP System Behavior
PEP implementations MUST treat premature closes as errors and any
data received as potentially truncated. The COPS protocol allows the
PEP system to find out whether truncation took place. A PEP system
detecting an incomplete close SHOULD recover gracefully.
PEP systems MUST send a closure alert before closing the connection.
Clients unprepared to receive any more data MAY choose not to wait
for the PDP system's closure alert and simply close the connection,
thus generating an incomplete close on the PDP side.
2.2.2. PDP System Behavior
COPS permits a PEP to close the connection at any time, and requires
PDPs to recover gracefully. In particular, PDPs SHOULD be prepared to
receive an incomplete close from the PEP, since a PEP often shuts
down for operational reasons unrelated to the transfer of policy
information between the PEP and PDP.
Implementation note: The PDP ordinarily expects to be able to
signal end of data by closing the connection. However, the PEP
may have already sent the closure alert and dropped the
connection.
PDP systems MUST attempt to initiate an exchange of closure alerts
with the PEP system before closing the connection. PDP systems MAY
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close the connection after sending the closure alert, thus generating
an incomplete close on the PEP side.
2.3. Port Number
The first data a PDP expects to receive from the PEP is a Client-Open
message. The first data a TLS server (and hence a COPS/TLS server)
expects to receive is the ClientHello. Consequently, COPS/TLS runs
over a separate port in order to distinguish it from COPS alone. When
COPS/TLS runs over a TCP/IP connection, the default TCP port at the
PDP is TBD. The PEP may use any TCP port. This does not preclude
COPS/TLS from running over another transport. TLS only presumes a
reliable connection-oriented data stream.
3. Endpoint Identification and Access Control
Implementations of COPS/TLS MUST use X.509 v3 certificates conforming
to [PKIX] to identify PDP and PEP systems. COPS/TLS systems MUST
perform certificate verification processing conforming to [PKIX].
If a subjectAltName extension of type dNSName or iPAddress is present
in the PDP's certificate, that MUST be used as the PDP identity.
Otherwise, the most specific Common Name field in the Subject field
of the certificate MUST be used.
Matching is performed using the matching rules specified by [PKIX].
If more than one identity of a given type is present in the
certificate (e.g. more than one dNSName name, a match in any one of
the set is considered acceptable.), the COPS system uses the first
name to match, except as noted below in the IP address checking
requirements. Names may contain the wildcard character * which is
considered to match any single domain name component or component
fragment. For example, *.a.com matches foo.a.com but not
bar.foo.a.com. f*.com matches foo.com but not foo.bar.com.
3.1. PDP Identity
Generally, COPS/TLS requests are generated by the PEP consulting
bootstrap policy information identifying authorized PDPs. As a
consequence, the hostname or IP address for the PDP is known to the
PEP. How this bootstrap policy information arrives at the PEP is
outside the scope of this document. However, all PEP implementations
MUST provide a mechanism to securely deliver or configure the
bootstrap policy. In particular, all PEP implementations MUST support
a mechanism to securely acquire the signing certificate of the
authorized certificate authorities issuing PDP certificates, and MUST
support a mechanism to securely acquire an access control list or
filter identifying its set of authorized PDPs.
PEP implementations that participate in multiple domains, such as
those on mobile platforms, MAY use different certificate authorities
and access control lists in each domain.
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Organizations may choose to deliver some or all of the bootstrap
policy configuration from an untrusted source, such as DHCP. In this
circumstance, COPS over TLS provides no protection from attack when
this untrusted source is compromised.
If the PDP hostname or IP address is available via the access control
mechanism, the PEP MUST check it against the PDP's identity as
presented in the PDP's TLS Certificate message.
In some cases the bootstrap policy will identify the authorized PDP
only by an IP address of the PDP system. In this case, the
subjectAltName MUST be present in the certificate, and it MUST
include an iPAdress format matching the expected name of the policy
server.
If the hostname of the PDP does not match the identity in the
certificate, a PEP on a user oriented system MUST either notify the
user (PEP systems MAY afford the user the opportunity to continue
with the connection in any case) or terminate the connection with a
bad certificate error. PEPs on unattended systems MUST log the error
to an appropriate audit log (if available) and MUST terminate the
connection (with a bad certificate error). Unattended PEP systems MAY
provide a configuration setting that disables this check, but then
MUST provide a setting which enables it.
3.2. PEP Identity
When PEP systems are not access controlled, the PDP need have no
external knowledge of what the PEP's identity ought to be and so
checks are neither possible nor necessary. In this case, there is no
requirement for PEP systems to register with a certificate authority,
and COPS over TLS uses one-way authentication, of the PDP to the PEP.
When PEP systems are access controlled, PEPs must be PKI clients in
the sense of [PKIX]. In this case, COPS over TLS uses two-way
authentication, and the PDP MUST perform the same identity checks for
the PEPs as described above for the PDP.
When access controls are in effect at the PDP, PDP implementations
MUST have a mechanism to securely acquire the signing certificates of
the certificate authorities issuing certificates to any of the PEPs
they support.
4. IANA Considerations
COPS over TLS uses a separate TCP port from COPS. IANA should assign
the value TBD to this port.
5. Security Considerations
This entire document concerns security.
6. Acknowledgements
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This document freely plagiarizes and adapts Eric Rescorla's similar
document RFC2818 that specifies how HTTP runs over TLS. Discussions
with David Durham and Ylian Sainte-Hillaire also lead to improvements
in this document.
7. References
[COPS] Durham, D., Boyle, J., Cohen, R., Herzog, R., Rajan, R.,
Sastry, A., "The COPS (Common Open Policy Service) Protocol", RFC
2748, January 200.
[PKIX] Housley, R., Ford, W., Polk, W., Solo, D., "Internet Public
Key Infrastructure: Part I: X.509 Certificate and CRL Profile",
RFC 2459, January 1999.
[RFC2026] Bradner, S., "The Internet Standards Process - Revision
3", RFC 2026, October 1996
[RFC2119] Bradner, S., "Key Words for use in RFCs to indicate
Requirement Levels", RFC 2119, March 1997.
[TLS] Dierks, T., Allen, C., "The TLS Protocol", RFC2246, January
1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC2818, May 2000.
8. Author Addresses
Jesse R. Walker
Intel Corporation
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
jesse.walker@intel.com
Amol Kulkarni
Intel Corporation
JF3-206
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
amol.kulkarni@intel.com
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