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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 4261

     Internet Draft                                       Jesse Walker
     Expiration: November 2003                           Amol Kulkarni
     File: draft-ietf-rap-cops-tls-06.txt                  Intel Corp.
 
 
 
                               COPS Over TLS
 
                         Last Updated: May 23, 2003
 
 
 
 Status of this Memo
 
    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of [RFC2026].
 
    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups.  Note that
    other groups may also distribute working documents as Internet-
    Drafts.
 
    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or obsoleted by other
    documents at any time.  It is inappropriate to use Internet-Drafts
    as reference material or to cite them other than as "work in
    progress."
 
    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt
 
    The list of Internet-Draft Shadow Directories can be accessed at
    http://www.ietf.org/shadow.html.
 
 
 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 [RFC2119].
 
 
 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
    3  Separate Ports versus Upward Negotiation.......................3
    3.1 The COPS/TLS approach.........................................4
    3.2.1 The ClientSI object format..................................4
    3.2.2 Error Codes and Sub-Codes...................................5
    4  Usage Scenarios................................................5
    4.1 Security Mandatory on both, Client and Server.................6
    4.2 Security Mandatory on Client and Optional on Server...........6
    4.3 Security Optional on Client and Mandatory on Server...........6
    4.4 Security Optional on both, Client and Server..................6
    4.5 Security Mandatory on Client but not supported by Server......6
    4.6 Security Optional on Client but not supported by Server.......6
    4.7 Security Mandatory on Server but not supported by Client......6
    4.8 Security Optional on Server but not supported by Client.......6
    5  Secure Connection Initiation...................................7
    6  Connection Closure.............................................7
    6.1.  PEP System Behavior.........................................7
    6.2.  PDP System Behavior.........................................8
    7  Port Number....................................................8
    8  Endpoint Identification and Access Control.....................8
    8.1  PDP Identity.................................................9
    8.2  PEP Identity................................................10
    9  Other Considerations..........................................10
    9.1 Backward Compatibility.......................................10
    9.2 IANA Considerations..........................................10
    10  Security Considerations......................................10
    11  Acknowledgements.............................................10
    12 References....................................................10
    12.1 Normative References........................................10
    12.2 Informative References......................................11
    13 Author Addresses..............................................11
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 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 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 [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. The main advantage of this strategy
    is that it is very simple to implement, with no modifications needed
    to existing insecure implementations. Thus it is the most popular
    approach. The disadvantage, however, is that it doesn't scale well,
    with a new port required for each secure implementation. Hence, the
    IESG discourages designers from using the strategy.
 
    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 in the protocol being secured
    so that it can support the upward negotiation. There is also a high
    handshake overhead involved in this method.
 
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 3.1 The COPS/TLS approach
 
    COPS/TLS uses a combination of both these approaches to achieve
    simultaneous operation with COPS/TCP. Initially, the authors had
    hoped to use the Separate Ports strategy for implementing COPS/TLS,
    however, due to the reluctance of the IESG to assign a well-known
    port, they settled on the following approach.
 
    When the COPS/TLS server is initialized, it SHOULD bind to any non-
    well-known port of its choice. The standard COPS server running over
    TCP MUST know the TCP port on which COPS/TLS is running. How this is
    achieved is outside the scope of this document.
 
    The system acting as the PEP also acts as the TLS client. It needs
    to first connect to the COPS/TCP server, from where it can be
    redirected to the COPS/TLS server.
 
    During the initial negotiation with the COPS/TCP server, the Message
    Integrity Object MUST be used to authenticate the validity of the
    COPS messages. The use of the integrity object is described in
    [RFC2748]. How the keys indicated by the Integrity Object are shared
    between the Client and Server is outside the scope of this document.
 
 3.2 Object Format and Error Codes
 
    This section describes the ClientSI object sent in the ClientOpen
    message and the error codes the server returns.
 
 3.2.1 The ClientSI object format
 
 
          0         1          2          3
    +----------+----------+----------+----------+
    |    Length (Octets)  | C-Num=9  | C-Type=2 |
    +----------+----------+----------+----------+
    |       Protocol      |        Flags        |
    +----------+----------+----------+----------+
    |          :          :          :          |
    //         :          :          :         //
    +----------+----------+----------+----------+
    |       Protocol      |        Flags        |
    +----------+----------+----------+----------+
 
 
    Protocol:
         1 = TLS
 
    Flags:
         0 = Protocol Support Optional
         1 = Protocol Support Required
 
 
 
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    This ClientSI object MUST be included with the ClientOpen message
    (Client Type = 0) when the client supports security. For each
    supported protocol, there MUST be a 32 bit Protocol+Flags pair
    appended to the object. At present, only one protocol (TLS) is
    described. However, the ClientSI object definition is general enough
    to allow addition of new protocols in the future.
    If multiple protocols are supported by the client, it MUST ensure
    that no more than one has the 'Protocol Support Required' flag set.
    Note that it is also valid to mark all protocols as optional.
 
 3.2.2 Error Codes and Sub-Codes
 
    This section adds to, and modifies, the error codes described in
    section 2.2.8 (Error Object) of [RFC2748].
 
    Error Code: 12 = Redirect to Preferred Server:
                Sub-code:
                  0 = Regular redirect (no security necessary)
                  1 = Use TLS
    Error Code: 16 = Security Failure
                17 = Security Required
 
    A new error sub-code has been added to the pre-existing error code
    12. The sub-code informs the client that it SHOULD use TLS when
    connecting to the redirected server. In the future, more sub-codes
    may be added to specify additional protocols.
 
    Error Code 17 SHOULD be used by either Client or Server if they
    require security but the other side doesn't support it.
 
 4 Usage Scenarios
 
    When the client needs to open a secure connection with the server,
    it SHOULD first connect to the non-secure port, and send a Client
    Open message with a ClientType=0.
 
    The policies implemented on the client dictate whether security is
    mandatory or optional.
 
    If the policies specify that security is mandatory, the above-
    mentioned ClientSI object MUST be included in the Client Open
    message. This object MUST list one protocol as required by setting
    the corresponding flag to 1.
 
    If the policies do not explicitly specify that a secure connection
    is required, the client SHOULD include the ClientSI object, listing
    protocol support as optional.
 
    Note that if the client's policies specifically prohibit a secure
    connection, it MAY attempt to establish a non-secure connection.
 
    Based on the client's policies and the server's policy requirements
    for the client, the following scenarios occur:
 
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 4.1 Security Mandatory on both, Client and Server
 
    The server MUST send a ClientClose message with a Redirect object,
    redirecting the client to the COPS/TLS secure port. Additionally,
    the error object included in the ClientClose message MUST have the
    error code = 12 and sub code = 1.
 
 4.2 Security Mandatory on Client and Optional on Server
 
    The server SHOULD send a ClientClose message with a Redirect object,
    redirecting the client to the COPS/TLS secure port. Additionally,
    the error object included in the ClientClose message MUST have the
    error code = 12 and sub code = 1.
 
    If the server does not redirect the client to the secure port, it
    MUST send a ClientClose with the error code 16.
 
 4.3 Security Optional on Client and Mandatory on Server
 
    The server MUST send a ClientClose message with a Redirect object,
    redirecting the client to the COPS/TLS secure port. Additionally,
    the error object included in the ClientClose message MUST have the
    error code = 12 and sub code = 1.
 
 4.4 Security Optional on both, Client and Server
 
    The server SHOULD send a ClientClose message with a Redirect object,
    redirecting the client to the COPS/TLS secure port. Additionally,
    the error object included in the ClientClose message MUST have the
    error code = 12 and sub code = 1.
 
    Optionally, the server MAY proceed to establish an insecure
    connection over COPS/TCP.
 
 4.5 Security Mandatory on Client but not supported by Server
 
    The server MUST send a ClientClose with the error code 16.
 
 4.6 Security Optional on Client but not supported by Server
 
    The server SHOULD attempt to establish a non-secure connection with
    the client.
 
 4.7 Security Mandatory on Server but not supported by Client
 
    If security is required by the server it MUST send a ClientClose
    with the error code 16.
 
 4.8 Security Optional on Server but not supported by Client
 
    The server it MAY attempt to establish a non-secure connection with
    the client.
 
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 5 Secure Connection Initiation
 
    Once the PEP receives a redirect from the COPS/TCP server, it
    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
    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.
 
 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
 
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    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.
 
 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 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 TCP
    port is any non-well-known port of the PDP's choice. This port MUST
    be communicated to the COPS/TCP server running on the well-known
    COPS TCP port. 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.
 
 8  Endpoint Identification and Access Control
 
    Implementations of COPS/TLS MUST use X.509 v3 certificates
    conforming to [RFC2459] to identify PDP and PEP systems. COPS/TLS
    systems MUST perform certificate verification processing conforming
    to [RFC2459]. In case the Certificate Authority cannot be accessed,
    communication MAY revert to insecure.
 
    If a subjectAltName extension of type dNSName or iPAddress is
    present in the PDP's certificate, that MUST be used as the PDP
 
 
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    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
    [RFC2459]. 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.
 
 8.1  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.
 
    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
 
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    MAY provide a configuration setting that disables this check, but
    then MUST provide a setting which enables it.
 
 8.2  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 [RFC2459]. 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.
 
 9 Other Considerations
 
 9.1 Backward Compatibility
    The client and server SHOULD be backward compatible with peers that
    do not support security. A client SHOULD be able to handle errors
    generated by a server which does not understand the ClientSI object
    mentioned above. Similarly, if a server receives a ClientOpen for
    Client type=0, which does not contain the ClientSI object, it SHOULD
    assume that the client wishes to open a non-secure connection and
    proceed accordingly.
 
 9.2 IANA Considerations
 
    This draft defines some new error codes and sub codes which require
    IANA approval. Section 3.2.2 has more details on these codes.
 
 10  Security Considerations
 
    This entire document concerns security.
 
 11  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.
 
 12  References
 12.1 Normative References
 
 
 
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       [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 200.
 
       [RFC2459] Housley, R., Ford, W., Polk, W., Solo, D., "Internet
       Public Key Infrastructure: Part I: X.509 Certificate and CRL
       Profile", RFC 2459, January 1999.
 
       [RFC2246] Dierks, T., Allen, C., "The TLS Protocol", RFC 2246,
       January 1999.
 
 12.2 Informative References
 
       [RFC2818] Rescorla, E., "HTTP Over TLS", RFC2818, May 2000.
 
 13  Author Addresses
 
       Jesse R. Walker
       Intel Corporation
       2111 N.E. 25th Avenue
       Hillsboro, OR  97214
       USA
       jesse.walker[at]intel.com
 
       Amol Kulkarni
       Intel Corporation
       JF3-206
       2111 N.E. 25th Avenue
       Hillsboro, OR  97214
       USA
       amol.kulkarni[at]intel.com
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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