Internet Draft Jesse Walker
Expiration: June 2005 Amol Kulkarni, Ed.
File: draft-ietf-rap-cops-tls-10.txt Intel Corp.
COPS Over TLS
Last Updated: December 1, 2004
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667 [RFC3667]. By submitting this Internet-
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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
[RFC2119].
Abstract
This document describes how to use Transport Layer Security (TLS)
to secure Common Open Policy Service (COPS) connections over the
Internet.
This document also updates RFC 2748 by modifying the contents of
the Client-Accept message.
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Table Of Contents
Glossary..........................................................3
1 Introduction...................................................3
2 COPS Over TLS..................................................3
3 Separate Ports versus Upward Negotiation.......................3
4 COPS/TLS Objects and Error codes...............................4
4.1 The TLS Message Integrity Object (Integrity-TLS)..............4
4.2 Error Codes...................................................4
5 COPS/TLS Secure Connection Initiation..........................5
5.1 PEP Initiated Security Negotiation............................5
5.2 PDP Initiated Security Negotiation............................6
6 Connection Closure.............................................6
6.1 PEP System Behavior...........................................7
6.2 PDP System Behavior...........................................7
7 Endpoint Identification and Access Control.....................7
7.1 PDP Identity..................................................8
7.2 PEP Identity..................................................9
8 Backward Compatibility.........................................9
9 IANA Considerations.............................................9
10 Security Considerations.......................................10
11 References....................................................10
11.1 Normative References........................................10
11.2 Informative References......................................10
12 Author Addresses.............................................11
13 IPR Disclosure Acknowledgement...............................11
14 Disclaimer of Validity.......................................11
15 Copyright Statement..........................................11
16 Disclaimer...................................................12
17 Acknowledgements.............................................12
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Glossary
COPS - Common Open Policy Service. See [RFC2748].
COPS/TCP - A plain-vanilla implementation of COPS.
COPS/TLS - A secure implementation of COPS using TLS.
PDP - Policy Decision Point. Also referred to as the Policy
Server. See [RFC2753].
PEP - Policy Enforcement Point. Also referred to as the Policy
Client. See [RFC2753].
1 Introduction
COPS [RFC2748] 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 confidentiality. 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 [RFC2246] 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 similar to how you would
use COPS over TCP (COPS/TCP). Apart from a specific procedure used
to initialize the connection, there is no difference between
COPS/TLS and COPS/TCP.
3 Separate Ports versus Upward Negotiation
There are two ways in which insecure and secure versions of the same
protocol can be run simultaneously.
In the first method, the secure version of the protocol is also
allocated a well-known port. This strategy of having well-known port
numbers for both, the secure and insecure versions, is known as
'Separate Ports'. The clients requiring security can simply connect
to the well-known secure port. This method is easy to implement,
with no modifications needed to existing insecure implementations.
The disadvantage, however, is that it doesn't scale well, with a new
port required for each secure implementation. More problems with
this approach have been listed in [RFC2595].
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The second method is known as 'Upward Negotiation'. In this method,
the secure and insecure versions of the protocol run on the same
port. The client connects to the server, both discover each others'
capabilities, and start security negotiations if desired. This
method usually requires some changes to the protocol being secured.
COPS/TLS uses the Upward Negotiation method to secure COPS messages.
4 COPS/TLS Objects and Error codes
This section describes the COPS objects and error codes needed to
support COPS/TLS.
4.1 The TLS Message Integrity Object (Integrity-TLS)
The TLS Integrity object is used by the PDP and the PEP to start the
TLS negotiation. This object should be included only in the Client-
Open or Client-Accept messages. It MUST NOT be included in any other
COPS message.
0 1 2 3
+----------+----------+----------+----------+
| Length (Octets) | C-Num=16 | C-Type=2 |
+----------+----------+----------+----------+
| //////// | Flags |
+----------+----------+----------+----------+
Note: //// implies the field is reserved, set to 0 and should be
ignored on receipt.
Flags: 16 bits
0x01 = StartTLS
This flag indicates that the sender of the message
wishes to initiate a TLS handshake.
The Client-Type of any message containing this object MUST be 0.
Client-Type 0 is used to negotiate COPS connection level security
and must only be used during the connection establishment phase.
Please refer to section 4.1 of [RFC2748] for more details.
4.2 Error Codes
This section uses the error codes described in section 2.2.8 (Error
Object) of [RFC2748].
Error Code: 13= Unknown COPS Object:
Sub-code (octet 2) contains the unknown object's C-Num and (octet 3)
contains unknown object's C-Type. If the PEP or PDP does not support
TLS, the C-Num specified will be 16 and the C-Type will be 2. This
demonstrates that the TLS version of the Integrity object not known.
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This error code should be used by either PEP or PDP to indicate a
security-related connection closure if it cannot support a TLS
connection for the COPS protocol.
If the PDP wishes to negotiate a different security mechanism than
requested by the PEP in the Client-Open, it should send the
following error code:
Error Code: 15= Authentication Required
Where the Sub-code (octet 2) contains the C-Num=16 value for the
Integrity Object and (octet 3) will specify the PDP
required/preferred Integrity object C-Type. If the server does not
support any form of COPS-Security, it will set the Sub-code (octet
2) to 16 and (octet 3) to zero instead, signifying that no type of
the Integrity object is supported.
5 COPS/TLS Secure Connection Initiation
Security negotiation may be initiated either by the PDP or the PEP.
The PEP can initiate a negotiation via a Client-Open message, while
a PDP can initiate a negotiation via a Client-Accept message.
Once the TLS connection is established, all COPS data MUST be sent
as TLS "application data".
5.1 PEP Initiated Security Negotiation
A PEP MAY initiate a TLS security negotiation with a PDP using the
Client-Open message. To do this, the Client-Open message MUST have a
Client-Type of 0 and MUST include the Integrity-TLS object.
Upon receiving the Client-Open message, the PDP SHOULD respond with
a Client-Accept message containing the Integrity-TLS object.
Note that in order to carry the Integrity-TLS object, the contents
of the Client-Accept message defined in section 3.7 of [RFC2748]
need not change, other than the C-Type of the integrity object
contained there-in should now be C-Type=2. For Example:
<Client-Accept> ::= <Common Header>
<KA Timer>
[<ACCT Timer>]
[<Integrity (C-Num=16, C-Type=2)>]
Upon receiving the appropriate Client-Accept message, the PEP SHOULD
initiate the TLS handshake.
The message exchange is as follows:
C: Client-Open (Client-Type = 0, Integrity-TLS)
S: Client-Accept (Client-Type = 0, Integrity-TLS)
<TLS handshake>
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C/S: <...further messages...>
In case the PDP does not wish to open a secure connection with the
PEP, it MUST reply with a Client-Close message and close the
connection. The Client-Close message MUST include the error code
15=Authentication required, with the Sub-code (octet 2) set to 16
for the Integrity object's C-Num and (octet 3) set to the C-Type
corresponding to the server's preferred Integrity type or zero for
no security.
A PEP requiring the Integrity-TLS object in a Client-Accept message
MUST close the connection if the Integrity-TLS object is missing. It
MUST include the error code 15= Authentication required, with the
Sub-code (octet 2) containing the required Integrity object's C-
Num=16 and (octet 3) containing the required Integrity object's C-
Type=2, in the ensuing Client-Close message.
5.2 PDP Initiated Security Negotiation
The PEP initially opens a TCP connection with the PDP on the
standard COPS port and sends a Client-Open message. This Client-Open
message MUST have a Client-Type of 0.
The PDP SHOULD then reply with a Client-Accept message. In order to
signal the PEP to start the TLS handshake, the PDP MUST include the
Integrity-TLS object in the Client-Accept message.
Upon receiving the Client-Accept message with the Integrity-TLS
object, the PEP SHOULD initiate the TLS handshake. If for any reason
the PEP cannot initiate the handshake, it MUST close the connection.
The message exchange is as follows:
C: Client-Open (Client-Type = 0)
S: Client-Accept (Client-Type = 0, Integrity-TLS)
<TLS handshake>
C/S: <...further messages...>
After receiving the Client-Accept, the PEP MUST NOT send any
messages until the TLS handshake is complete. Upon receiving any
message from the PEP before the TLS handshake starts, the PDP MUST
issue a Client-Close message with an error code 15= Authentication
Required.
A PDP wishing to negotiate security with a PEP having an existing
non-secure connection MUST send a Client-Close with the error code
15= Authentication required, with the Sub-code (octet 2) containing
the required Integrity object's C-Num=16 and (octet 3) containing
the required Integrity object's C-Type=2 and wait for the PEP to
reconnect. Upon receiving the Client-Open message, it SHOULD use the
Client-Accept message to initiate security negotiation.
6 Connection Closure
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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.
6.1 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.
PEPs 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.
6.2 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
close the connection after sending the closure alert, thus
generating an incomplete close on the PEP side.
7 Endpoint Identification and Access Control
All PEP implementations of COPS/TLS MUST support an access control
mechanism to identify authorized PDPs. This requirement provides a
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level of assurance that the policy arriving at the PEP is actually
valid. PEP deployments 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, deployments MAY choose not to
use 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 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.
Implementations of COPS/TLS MUST use X.509 v3 certificates
conforming to [RFC3280] to identify PDP and PEP systems. COPS/TLS
systems MUST perform certificate verification processing conforming
to [RFC3280].
If a subjectAltName extension of type dNSName or iPAddress is
present in the PDP's certificate, it MUST be used as the PDP
identity. If both types are present, dNSName SHOULD be used as the
PDP identity. If neither of the types is present, the most specific
Common Name field in the Subject field of the certificate SHOULD be
used.
Matching is performed using the matching rules specified by
[RFC3280]. If more than one identity of a given type is present in
the certificate (e.g. more than one dNSName name in the
subjectAltName certificate extension), a match in any one of the
provided identities is acceptable. Generally, the COPS system uses
the first name for matching, except as noted below in the IP
address checking requirements.
7.1 PDP Identity
Generally, COPS/TLS requests are generated by the PEP consulting
bootstrap policy information that identifies PDPs that the PEP is
authorized to connect to. This policy provides the PEP with the
hostname or IP address of the PDP. 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.
All PEP implementations MUST be able to securely acquire the trust
anchor for each authorized Certification Authority (CA) that issues
PDP certificates. Also, the PEPs MUST support a mechanism to
securely acquire an access control list or filter identifying the
set of authorized PDPs associated with each CA.
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PEP deployments that participate in multiple domains, such as those
on mobile platforms, MAY use different CAs and access control lists
in each domain.
If the PDP hostname or IP address is available via the bootstrap
policy, 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.
7.2 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 the subjects
of end entity certificates [RFC3280]. 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 trust anchor for each
authorized Certification Authority (CA) that issues certificates to
supported PEPs.
8 Backward Compatibility
The PEP and PDP SHOULD be backward compatible with peers that have
not been modified to support COPS/TLS. They SHOULD handle errors
generated in response to the Integrity-TLS object.
9 IANA Considerations
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For the Integrity-TLS object for Client-Type 0, the IANA shall add
the following Flags value:
0x01 = StartTLS
Further values for the Flags field and the reserved field can only
be assigned by IETF Consensus rule as defined in [RFC2434].
10 Security Considerations
A COPS PDP and PEP MUST check the results of the TLS negotiation to
see whether an acceptable degree of authentication and privacy have
been achieved. If the negotiation has resulted in unacceptable
algorithms or key lengths, either side MAY choose to terminate the
connection.
A man-in-the-middle attack can be launched by deleting the
Integrity-TLS object or altering the Client-Open or Client-Accept
messages. If security is required, the PEP and PDP bootstrap policy
must specify this, and PEP and PDP implementations should reject
Client-Open or Client-Accept messages that fail to include an
Integrity-TLS object.
11 References
11.1 Normative References
[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.
[RFC2748] Durham, D., Boyle, J., Cohen, R., Herzog, R., Rajan,
R., Sastry, A., "The COPS (Common Open Policy Service) Protocol",
RFC 2748, January 2000.
[RFC3280] Housley, R., Ford, W., Polk, W., Solo, D., "Internet
X.509 Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile ", RFC 3280, April 2002.
[RFC2246] Dierks, T., Allen, C., "The TLS Protocol", RFC 2246,
January 1999.
11.2 Informative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
2595, June 1999.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP
over Transport Layer Security", RFC 3207, February 2002.
[RFC2434] Alvestrand, H., Narten, T., "Guidelines for writing an
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IANA Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
12 Author Addresses
Amol Kulkarni
Intel Corporation
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
amol[dot]kulkarni[at]intel[dot]com
Jesse R. Walker
Intel Corporation
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
jesse[dot]walker[at]intel[dot]com
13 IPR Disclosure Acknowledgement
By submitting this Internet-Draft, we certify that any applicable
patent or other IPR claims of which we are aware have been
disclosed, and any of which we become aware will be disclosed, in
accordance with RFC 3668.
14 Disclaimer of Validity
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology described
in this document or the extent to which any license under such
rights might or might not be available; nor does it represent that
it has made any independent effort to identify any such rights.
Information on the procedures with respect to rights in RFC
documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
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The IETF invites any interested party to bring to its attention any
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this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
15 Copyright Statement
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Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
16 Disclaimer
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
17 Acknowledgements
This document freely plagiarizes and adapts Eric Rescorla's similar
document [RFC2818] that specifies how HTTP runs over TLS.
Discussions with David Durham, Scott Hahn and Ylian Sainte-Hillaire
also lead to improvements in this document.
The authors wish to thank Uri Blumenthal for doing a thorough
security review of the document.
Funding for the RFC Editor function is currently provided by the
Internet Society.
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