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Network Working Group                                          J. WalkerRequest for Comments: 4261                              A. Kulkarni, Ed.Updates:2748                                                Intel Corp.Category: Standards Track                                  December 2005Common Open Policy Service (COPS)Over Transport Layer Security (TLS)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).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 updatesRFC 2748 by modifying the contents of the   Client-Accept message.Walker & Kulkarni           Standards Track                     [Page 1]

RFC 4261                     COPS Over TLS                 December 2005Table Of Contents1. Introduction ....................................................22. COPS Over TLS ...................................................33. Separate Ports versus Upward Negotiation ........................34. COPS/TLS Objects and Error codes ................................44.1. The TLS Message Integrity Object (Integrity-TLS) ...........44.2. Error Codes ................................................45. COPS/TLS Secure Connection Initiation ...........................55.1. PEP Initiated Security Negotiation .........................55.2. PDP Initiated Security Negotiation .........................66. Connection Closure ..............................................76.1. PEP System Behavior ........................................76.2. PDP System Behavior ........................................87. Endpoint Identification and Access Control ......................87.1. PEP Identity ...............................................97.2. PDP Identity ...............................................98. Cipher Suite Requirements ......................................109. Backward Compatibility .........................................1010. IANA Considerations ...........................................1011. Security Considerations .......................................1112. Acknowledgements ..............................................1113. References ....................................................1213.1. Normative References .....................................1213.2. Informative References ...................................121.  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   (e.g., 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.Walker & Kulkarni           Standards Track                     [Page 2]

RFC 4261                     COPS Over TLS                 December 2005Glossary   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].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 inRFC 2119 [RFC2119].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, because a   new port is required for each secure implementation.  More problems   with this approach have been listed in [RFC2595].   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.Walker & Kulkarni           Standards Track                     [Page 3]

RFC 4261                     COPS Over TLS                 December 2005   In view of the many issues with the Separate Ports approach, the   authors have decided to use the Upward Negotiation method for   COPS/TLS.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 tosection 4.1 of [RFC2748] for more details.4.2.  Error Codes   This section uses the error codes described insection 2.2.8 (Error   Object) of [RFC2748].   Error Code:                13= Unknown COPS Object:Walker & Kulkarni           Standards Track                     [Page 4]

RFC 4261                     COPS Over TLS                 December 2005   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 MUST be 16 and the C-Type MUST be 2.  This   demonstrates that the TLS version of the Integrity object is not   known.   This error code MUST 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 MUST 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) MUST specify the PDP   required/preferred Integrity object C-Type.  If the server does not   support any form of COPS-Security, it MUST 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 by either 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 insection 3.7 of [RFC2748] need   not change, except that the C-Type of the integrity object contained   there-in should now be C-Type=2.  For Example:Walker & Kulkarni           Standards Track                     [Page 5]

RFC 4261                     COPS Over TLS                 December 2005      <Client-Accept> ::= <Common Header>                          <KA Timer>                          [<ACCT Timer>]                          [<Integrity (C-Num=16, C-Type=2)>]   Note also that this new format of the Client-Accept message does not   replace or obsolete the existing Client-Accept message format, which   can continue to be used for non-secure COPS session negotiations.   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>      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.   The ensuing Client-Close message 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=2.5.2.  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.Walker & Kulkarni           Standards Track                     [Page 6]

RFC 4261                     COPS Over TLS                 December 2005   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 then 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   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.Walker & Kulkarni           Standards Track                     [Page 7]

RFC 4261                     COPS Over TLS                 December 2005   PEP systems SHOULD 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 the 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   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].Walker & Kulkarni           Standards Track                     [Page 8]

RFC 4261                     COPS Over TLS                 December 2005   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 type 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 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.  PEP Identity   When PEP systems are not access controlled, the PDP does not need   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.7.2.  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 (ACL) or filter identifying   the set of authorized PDPs associated with each CA.  Deployments must   take care to avoid circular dependencies in accessing trust anchorsWalker & Kulkarni           Standards Track                     [Page 9]

RFC 4261                     COPS Over TLS                 December 2005   and ACLs.  At a minimum, trust anchors and ACLs may be installed   manually.   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 iPAddress 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 that enables it.8. Cipher Suite Requirements   Implementations MUST support the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher   suite.  All other cipher suites are optional.9.  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.10.  IANA Considerations   The IANA has added the following C-Num, C-Type combination for the   Integrity-TLS object to the registry athttp://www.iana.org/assignments/cops-parameters:   0x10  0x02    Message Integrity, Integrity-TLS      [RFC4261]Walker & Kulkarni           Standards Track                    [Page 10]

RFC 4261                     COPS Over TLS                 December 2005   For Client-Type 0, the IANA has added the following Flags value for   the Integrity-TLS object:      0x01 = StartTLS   Further, for Client-Type 0, the IANA has added the following text for   Error Sub-Codes:      Error Code: 15      Error Sub-Code:      Octet 2: C-Num of the Integrity object      Octet 3: C-Type of the supported/preferred Integrity object or               Zero.     Error-Code    Error-SubCode      Description                 Octet 2  Octet 3     ---------------------------------------------------       15          16        0        No security       15          16        2        Integrity-TLS supported/preferred   Further values for the Flags field and the reserved field can only be   assigned by IETF Consensus rule, as defined in [RFC2434].11.  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.12.  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.Walker & Kulkarni           Standards Track                    [Page 11]

RFC 4261                     COPS Over TLS                 December 200513.  References13.1.  Normative References   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2748] Durham, D., Boyle, J., Cohen, R., Herzog, S., Rajan, R.,             and A. Sastry, "The COPS (Common Open Policy Service)             Protocol",RFC 2748, January 2000.   [RFC2753] Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework             for Policy-based Admission Control",RFC 2753, January             2000.   [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet             X.509 Public Key Infrastructure Certificate and Certificate             Revocation List (CRL) Profile",RFC 3280, April 2002.   [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",RFC 2246, January 1999.13.2.  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.   [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an             IANA Considerations Section in RFCs",BCP 26,RFC 2434,             October 1998.Walker & Kulkarni           Standards Track                    [Page 12]

RFC 4261                     COPS Over TLS                 December 2005Authors' Addresses   Amol Kulkarni   Intel Corporation   2111 N.E. 25th Avenue   Hillsboro, OR  97214   USA   EMail: amol.kulkarni@intel.com   Jesse R. Walker   Intel Corporation   2111 N.E. 25th Avenue   Hillsboro, OR  97214   USA   EMail: jesse.walker@intel.comWalker & Kulkarni           Standards Track                    [Page 13]

RFC 4261                     COPS Over TLS                 December 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   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.Intellectual Property   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 inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Walker & Kulkarni           Standards Track                    [Page 14]