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RFC 3520 - Session Authorization Policy Element


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Network Working Group                                         L-N. Hamer
Request for Comments: 3520                                       B. Gage
Category: Standards Track                                Nortel Networks
                                                             B. Kosinski
                                                     Invidi Technologies
                                                                H. Shieh
                                                           AT&T Wireless
                                                              April 2003

                 Session Authorization Policy Element

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 (2003).  All Rights Reserved.

Abstract

   This document describes the representation of a session authorization
   policy element for supporting policy-based per-session authorization
   and admission control.  The goal of session authorization is to allow
   the exchange of information between network elements in order to
   authorize the use of resources for a service and to co-ordinate
   actions between the signaling and transport planes.  This document
   describes how a process on a system authorizes the reservation of
   resources by a host and then provides that host with a session
   authorization policy element which can be inserted into a resource
   reservation protocol (e.g., the Resource ReSerVation Protocol (RSVP)
   PATH message) to facilitate proper and secure reservation of those
   resources within the network.  We describe the encoding of session
   authorization information as a policy element conforming to the
   format of a Policy Data object (RFC 2750) and provide details
   relating to operations, processing rules and error scenarios.

Table of Contents

   1. Conventions used in this document..............................3
   2. Introduction...................................................3
   3. Policy Element for Session Authorization.......................4
      3.1 Policy Data Object Format..................................4
      3.2 Session Authorization Policy Element.......................4
      3.3 Session Authorization Attributes...........................4
        3.3.1 Authorizing Entity Identifier..........................6
        3.3.2 Session Identifier.....................................7
        3.3.3 Source Address.........................................7
        3.3.4 Destination Address....................................9
        3.3.5 Start time............................................10
        3.3.6 End time..............................................11
        3.3.7 Resources Authorized..................................11
        3.3.8 Authentication data...................................12
   4. Integrity of the AUTH_SESSION policy element..................13
      4.1 Shared symmetric keys.....................................13
        4.1.1 Operational Setting using shared symmetric keys.......13
      4.2 Kerberos..................................................14
        4.2.1. Operational Setting using Kerberos...................15
      4.3 Public Key................................................16
        4.3.1. Operational Setting for public key based
               authentication.......................................16
          4.3.1.1 X.509 V3 digital certificates.....................17
          4.3.1.2 PGP digital certificates..........................17
   5. Framework.....................................................18
      5.1 The coupled model.........................................18
      5.2 The associated model with one policy server...............18
      5.3 The associated model with two policy servers..............19
      5.4 The non-associated model..................................19
   6. Message Processing Rules......................................20
      6.1 Generation of the AUTH_SESSION by the authorizing entity..20
      6.2 Message Generation (RSVP Host)............................20
      6.3 Message Reception (RSVP-aware Router).....................20
      6.4 Authorization (Router/PDP)................................21
   7. Error Signaling...............................................22
   8. IANA Considerations...........................................22
   9. Security Considerations.......................................24
   10. Acknowledgments..............................................24
   11. Normative References.........................................25
   12. Informative References.......................................27
   13. Intellectual Property Statement..............................27
   14. Contributors.................................................28
   15. Authors' Addresses...........................................29
   16. Full Copyright Statement.....................................30

1. 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 BCP 14, RFC 2119
   [RFC-2119].

2. Introduction

   RSVP [RFC-2205] is one example of a resource reservation protocol
   that is used by a host to request specific services from the network
   for particular application data streams or flows.  RSVP requests will
   generally result in resources being reserved in each router along the
   data path.  RSVP allows users to obtain preferential access to
   network resources, under the control of an admission control
   mechanism.  Such admission control is often based on user or
   application identity [RFC-3182], however, it is also valuable to
   provide the ability for per-session admission control.

   In order to allow for per-session admission control, it is necessary
   to provide a mechanism for ensuring use of resources by a host has
   been properly authorized before allowing the reservation of those
   resources.  In order to meet this requirement, there must be
   information in the resource reservation message which may be used to
   verify the validity of the reservation request.  This can be done by
   providing the host with a session authorization policy element which
   is inserted into the resource reservation message and verified by the
   network.

   This document describes the session authorization policy element
   (AUTH_SESSION) used to convey information about the resources
   authorized for use by a session.  The host must obtain an
   AUTH_SESSION element from an authorizing entity via a session
   signaling protocol such as SIP [RFC-3261].  The host then inserts the
   AUTH_SESSION element into the resource reservation message to allow
   verification of the network resource request; in the case of RSVP,
   this element MUST be encapsulated in the Policy Data object [RFC-
   2750] of an RSVP PATH message.  Network elements verify the request
   and then process the resource reservation message based on admission
   policy.

   [RFC-3521] describes a framework in which a session authorization
   policy element may be utilized to contain information relevant to the
   network's decision to grant a reservation request.

3. Policy Element for Session Authorization

3.1 Policy Data Object Format

   The Session Authorization policy element conforms to the format of a
   POLICY_DATA object which contains policy information and is carried
   by policy based admission protocols such as RSVP.  A detailed
   description of the POLICY_DATA object can be found in "RSVP
   Extensions for Policy Control" [RFC-2750].

3.2 Session Authorization Policy Element

   In this section we describe a policy element (PE) called session
   authorization (AUTH_SESSION).  The AUTH_SESSION policy element
   contains a list of fields which describe the session, along with
   other attributes.

          +-------------+-------------+-------------+-------------+
          | Length                    | P-Type = AUTH_SESSION     |
          +-------------+-------------+-------------+-------------+
          // Session Authorization Attribute List                //
          +-------------------------------------------------------+

   Length: 16 bits
      The length of the policy element (including the Length and P-Type)
      is in number of octets (MUST be in multiples of 4) and indicates
      the end of the session authorization information block.

   P-Type: 16 bits (Session Authorization Type)
      AUTH_SESSION = 0x04
      The Policy element type (P-type) of this element.  The Internet
      Assigned Numbers Authority (IANA) acts as a registry for policy
      element types as described in [RFC-2750].

   Session Authorization Attribute List: variable length
      The session authorization attribute list is a collection of
      objects which describes the session and provides other information
      necessary to verify the resource reservation request. An initial
      set of valid objects is described in Section 3.3.

3.3 Session Authorization Attributes

   A session authorization attribute may contain a variety of
   information and has both an attribute type and subtype.  The
   attribute itself MUST be a multiple of 4 octets in length, and any
   attributes that are not a multiple of 4 octets long MUST be padded to
   a 4-octet boundary.  All padding bytes MUST have a value of zero.

      +--------+--------+--------+--------+
      | Length          | X-Type |SubType |
      +--------+--------+--------+--------+
      | Value ...
      +--------+--------+--------+--------+

   Length: 16 bits
      The length field is two octets and indicates the actual length of
      the attribute (including Length, X-Type and SubType fields) in
      number of octets.  The length does NOT include any bytes padding
      to the value field to make the attribute a multiple of 4 octets
      long.

   X-Type: 8 bits
      Session authorization attribute type (X-Type) field is one octet.
      IANA acts as a registry for X-Types as described in section 7,
      IANA Considerations.  Initially, the registry contains the
      following X-Types:

      1  AUTH_ENT_ID          The unique identifier of the entity which
                              authorized the session.

      2  SESSION_ID           Unique identifier for this session.

      3  SOURCE_ADDR          Address specification for the session
                              originator.

      4  DEST_ADDR            Address specification for the session
                              end-point.

      5  START_TIME           The starting time for the session.

      6  END_TIME             The end time for the session.

      7  RESOURCES            The resources which the user is authorized
                              to request.

      8  AUTHENTICATION_DATA  Authentication data of the session
                              authorization policy element.

   SubType: 8 bits
      Session authorization attribute sub-type is one octet in length.
      The value of the SubType depends on the X-Type.

   Value: variable length
      The attribute specific information.

3.3.1 Authorizing Entity Identifier

   AUTH_ENT_ID is used to identify the entity which authorized the
   initial service request and generated the session authorization
   policy element.  The AUTH_ENT_ID may be represented in various
   formats, and the SubType is used to define the format for the ID. The
   format for AUTH_ENT_ID is as follows:

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      AUTH_ENT_ID

   SubType
      The following sub-types for AUTH_ENT_ID are defined.  IANA acts as
      a registry for AUTH_ENT_ID sub-types as described in section 7,
      IANA Considerations.  Initially, the registry contains the
      following sub-types of AUTH_ENT_ID:

      1  IPV4_ADDRESS        IPv4 address represented in 32 bits

      2  IPV6_ADDRESS        IPv6 address represented in 128 bits

      3  FQDN                Fully Qualified Domain Name as defined in
                             RFC 1034 as an ASCII string.

      4  ASCII_DN            X.500 Distinguished name as defined in RFC
                             2253 as an ASCII string.

      5  UNICODE_DN          X.500 Distinguished name as defined in RFC
                             2253 as a UTF-8 string.

      6  URI                 Universal Resource Identifier, as defined
                             in RFC 2396.

      7  KRB_PRINCIPAL       Fully Qualified Kerberos Principal name
                             represented by the ASCII string of a
                             principal followed by the @ realm name as
                             defined in RFC 1510 (e.g.,
                             principalX@realmY).

      8  X509_V3_CERT        The Distinguished Name of the subject of
                             the certificate as defined in RFC 2253 as a
                             UTF-8 string.

      9  PGP_CERT            The PGP digital certificate of the
                             authorizing entity as defined in RFC 2440.

   OctetString
      Contains the authorizing entity identifier.

3.3.2 Session Identifier

   SESSION_ID is a unique identifier used by the authorizing entity to
   identify the request.  It may be used for a number of purposes,
   including replay detection, or to correlate this request to a policy
   decision entry made by the authorizing entity.  For example, the
   SESSION_ID can be based on simple sequence numbers or on a standard
   NTP timestamp.

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

    X-Type
      SESSION_ID

   SubType
      No subtypes for SESSION_ID are currently defined; this field MUST
      be set to zero.  The authorizing entity is the only network entity
      that needs to interpret the contents of the SESSION_ID therefore
      the contents and format are implementation dependent.

   OctetString
      Contains the session identifier.

3.3.3 Source Address

   SOURCE_ADDR is used to identify the source address specification of
   the authorized session.  This X-Type may be useful in some scenarios
   to make sure the resource request has been authorized for that
   particular source address and/or port.

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      SOURCE_ADDR

   SubType
      The following sub types for SOURCE_ADDR are defined.  IANA acts as
      a registry for SOURCE_ADDR sub-types as described in section 7,
      IANA Considerations.  Initially, the registry contains the
      following sub types for SOURCE_ADDR:

      1  IPV4_ADDRESS        IPv4 address represented in 32 bits

      2  IPV6_ADDRESS        IPv6 address represented in 128 bits

      3  UDP_PORT_LIST       list of UDP port specifications,
                             represented as 16 bits per list entry.

      4  TCP_PORT_LIST       list of TCP port specifications,
                             represented as 16 bits per list entry.

   OctetString
      The OctetString contains the source address information.

   In scenarios where a source address is required (see Section 5), at
   least one of the subtypes 1 through 2 (inclusive) MUST be included in
   every Session Authorization Data Policy Element.  Multiple
   SOURCE_ADDR attributes MAY be included if multiple addresses have
   been authorized.  The source address field of the resource
   reservation datagram (e.g., RSVP PATH) MUST match one of the
   SOURCE_ADDR attributes contained in this Session Authorization Data
   Policy Element.

   At most, one instance of subtype 3 MAY be included in every Session
   Authorization Data Policy Element.  At most, one instance of subtype
   4 MAY be included in every Session Authorization Data Policy Element.
   Inclusion of a subtype 3 attribute does not prevent inclusion of a
   subtype 4 attribute (i.e., both UDP and TCP ports may be authorized).

   If no PORT attributes are specified, then all ports are considered
   valid; otherwise, only the specified ports are authorized for use.

   Every source address and port list must be included in a separate
   SOURCE_ADDR attribute.

3.3.4 Destination Address

   DEST_ADDR is used to identify the destination address of the
   authorized session.  This X-Type may be useful in some scenarios to
   make sure the resource request has been authorized for that
   particular destination address and/or port.

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      DEST_ADDR

   SubType
      The following sub types for DEST_ADDR are defined.  IANA acts as a
      registry for DEST_ADDR sub-types as described in section 7, IANA
      Considerations.  Initially, the registry contains the following
      sub types for DEST_ADDR:

      1  IPV4_ADDRESS        IPv4 address represented in 32 bits

      2  IPV6_ADDRESS        IPv6 address represented in 128 bits

      3  UDP_PORT_LIST       list of UDP port specifications,
                             represented as 16 bits per list entry.

      4  TCP_PORT_LIST       list of TCP port specifications,
                             represented as 16 bits per list entry.

   OctetString
      The OctetString contains the destination address specification.

   In scenarios where a destination address is required (see Section 5),
   at least one of the subtypes 1 through 2 (inclusive) MUST be included
   in every Session Authorization Data Policy Element.  Multiple
   DEST_ADDR attributes MAY be included if multiple addresses have been
   authorized.  The destination address field of the resource

   reservation datagram (e.g., RSVP PATH) MUST match one of the
   DEST_ADDR attributes contained in this Session Authorization Data
   Policy Element.

   At most, one instance of subtype 3 MAY be included in every Session
   Authorization Data Policy Element.  At most, one instance of subtype
   4 MAY be included in every Session Authorization Data Policy Element.
   Inclusion of a subtype 3 attribute does not prevent inclusion of a
   subtype 4 attribute (i.e., both UDP and TCP ports may be authorized).

   If no PORT attributes are specified, then all ports are considered
   valid; otherwise, only the specified ports are authorized for use.

   Every destination address and port list must be included in a
   separate DEST_ADDR attribute.

3.3.5 Start time

   START_TIME is used to identify the start time of the authorized
   session and can be used to prevent replay attacks.  If the
   AUTH_SESSION policy element is presented in a resource request, the
   network SHOULD reject the request if it is not received within a few
   seconds of the start time specified.

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      START_TIME

   SubType
      The following sub types for START_TIME are defined.  IANA acts as
      a registry for START_TIME sub-types as described in section 7,
      IANA Considerations.  Initially, the registry contains the
      following sub types for START_TIME:

      1  NTP_TIMESTAMP        NTP Timestamp Format as defined in
                              RFC 1305.

   OctetString
      The OctetString contains the start time.

3.3.6 End time

   END_TIME is used to identify the end time of the authorized session
   and can be used to limit the amount of time that resources are
   authorized for use (e.g., in prepaid session scenarios).

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      END_TIME

   SubType
      The following sub types for END_TIME are defined.  IANA acts as a
      registry for END_TIME sub-types as described in section 7, IANA
      Considerations.  Initially, the registry contains the following
      sub types for END_TIME:

      1  NTP_TIMESTAMP        NTP Timestamp Format as defined in
                              RFC 1305.

   OctetString
      The OctetString contains the end time.

3.3.7 Resources Authorized

   RESOURCES is used to define the characteristics of the authorized
   session.  This X-Type may be useful in some scenarios to specify the
   specific resources authorized to ensure the request fits the
   authorized specifications.

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      RESOURCES

   SubType
      The following sub-types for RESOURCES are defined.  IANA acts as a
      registry for RESOURCES sub-types as described in section 7, IANA
      Considerations.  Initially, the registry contains the following
      sub types for RESOURCES:

      1  BANDWIDTH     Maximum bandwidth (kbps) authorized.

      2  FLOW_SPEC     Flow spec specification as defined in RFC 2205.

      3  SDP           SDP Media Descriptor as defined in RFC 2327.

      4  DSCP          Differentiated services codepoint as defined in
                       RFC 2474.

   OctetString
      The OctetString contains the resources specification.

   In scenarios where a resource specification is required (see Section
   5), at least one of the subtypes 1 through 4 (inclusive) MUST be
   included in every Session Authorization Data Policy Element.
   Multiple RESOURCE attributes MAY be included if multiple types of
   resources have been authorized (e.g., DSCP and BANDWIDTH).

3.3.8 Authentication data

   The AUTHENTICATION_DATA attribute contains the authentication data of
   the AUTH_SESSION policy element and signs all the data in the policy
   element up to the AUTHENTICATION_DATA.  If the AUTHENTICATION_DATA
   attribute has been included in the AUTH_SESSION policy element, it
   MUST be the last attribute in the list.  The algorithm used to
   compute the authentication data depends on the AUTH_ENT_ID SubType
   field.  See Section 4 entitled Integrity of the AUTH_SESSION policy
   element.

   A summary of AUTHENTICATION_DATA attribute format is described below.

      +-------+-------+-------+-------+
      | Length        |X-Type |SubType|
      +-------+-------+-------+-------+
      | OctetString ...
      +-------+-------+-------+-------+

   Length
      Length of the attribute, which MUST be > 4.

   X-Type
      AUTHENTICATION_DATA

   SubType
      No sub types for AUTHENTICATION_DATA are currently defined.  This
      field MUST be set to 0.

   OctetString
      The OctetString contains the authentication data of the
      AUTH_SESSION.

4. Integrity of the AUTH_SESSION policy element

   This section describes how to ensure the integrity of the policy
   element is preserved.

4.1 Shared symmetric keys

   In shared symmetric key environments, the AUTH_ENT_ID MUST be of
   subtypes: IPV4_ADDRESS, IPV6_ADDRESS, FQDN, ASCII_DN, UNICODE_DN or
   URI.  An example AUTH_SESSION policy element is shown below.

         +--------------+--------------+--------------+--------------+
         | Length                      | P-type = AUTH_SESSION       |
         +--------------+--------------+--------------+--------------+
         | Length                      |SESSION_ID    |     zero     |
         +--------------+--------------+--------------+--------------+
         | OctetString (The session identifier) ...
         +--------------+--------------+--------------+--------------+
         | Length                      | AUTH_ENT_ID  | IPV4_ADDRESS |
         +--------------+--------------+--------------+--------------+
         | OctetString (The authorizing entity's Identifier) ...
         +--------------+--------------+--------------+--------------+
         | Length                      |AUTH DATA.    |     zero     |
         +--------------+--------------+--------------+--------------+
         |                          KEY_ID                           |
         +--------------+--------------+--------------+--------------+
         | OctetString (Authentication data) ...
         +--------------+--------------+--------------+--------------+

4.1.1 Operational Setting using shared symmetric keys

   This assumes both the Authorizing Entity and the Network router/PDP
   are provisioned with shared symmetric keys and with policies
   detailing which algorithm to be used for computing the authentication
   data along with the expected length of the authentication data for
   that particular algorithm.

   Key maintenance is outside the scope of this document, but
   AUTH_SESSION implementations MUST at least provide the ability to
   manually configure keys and their parameters locally.  The key used

   to produce the authentication data is identified by the AUTH_ENT_ID
   field.  Since multiple keys may be configured for a particular
   AUTH_ENT_ID value, the first 32 bits of the AUTH_DATA field MUST be a
   key ID to be used to identify the appropriate key.  Each key must
   also be configured with lifetime parameters for the time period
   within which it is valid as well as an associated cryptographic
   algorithm parameter specifying the algorithm to be used with the key.
   At a minimum, all AUTH_SESSION implementations MUST support the
   HMAC-MD5-128 [RFC-2104], [RFC-1321] cryptographic algorithm for
   computing the authentication data.  New algorithms may be added by
   the IETF standards process.

   It is good practice to regularly change keys.  Keys MUST be
   configurable such that their lifetimes overlap allowing smooth
   transitions between keys.  At the midpoint of the lifetime overlap
   between two keys, senders should transition from using the current
   key to the next/longer-lived key.  Meanwhile, receivers simply accept
   any identified key received within its configured lifetime and reject
   those that are not.

4.2 Kerberos

   In a Kerberos environment, the AUTH_ENT_ID MUST be of the subtype
   KRB_PRINCIPAL.  The KRB_PRINCIPAL field is defined as the Fully
   Qualified Kerberos Principal name of the authorizing entity.
   Kerberos [RFC-1510] authentication uses a trusted third party (the
   Kerberos Distribution Center - KDC) to provide for authentication of
   the AUTH_SESSION to a network server.  It is assumed that a KDC is
   present and both host and verifier of authentication information
   (authorizing entity and router/PDP) implement Kerberos
   authentication.

   An example of the Kerberos AUTH_DATA policy element is shown below.

      +--------------+--------------+--------------+--------------+
      | Length                      | P-type = AUTH_SESSION       |
      +--------------+--------------+--------------+--------------+
      | Length                      |SESSION_ID    |     zero     |
      +--------------+--------------+--------------+--------------+
      | OctetString (The session identifier) ...
      +--------------+--------------+--------------+--------------+
      | Length                      | AUTH_ENT_ID  | KERB_P.      |
      +--------------+--------------+--------------+--------------+
      | OctetString (The principal@realm name) ...
      +--------------+--------------+--------------+--------------+

4.2.1. Operational Setting using Kerberos

   An authorizing entity is configured to construct the AUTH_SESSION
   policy element that designates use of the Kerberos authentication
   method (KRB_PRINCIPAL) as defined in RFC 1510.  Upon reception of the
   resource reservation request, the router/PDP contacts the local KDC,
   with a KRB_AS_REQ message, to request credentials for the authorizing
   entity (principal@realm).  In this request, the client (router/PDP)
   sends (in cleartext) its own identity and the identity of the server
   (the authorizing entity taken from the AUTH_ENT_ID field) for which
   it is requesting credentials.  The local KDC responds with these
   credentials in a KRB_AS_REP message, encrypted in the client's key.
   The credentials consist of 1) a "ticket" for the server and 2) a
   temporary encryption key (often called a "session key").  The
   router/PDP uses the ticket to access the authorizing entity with a
   KRB_AP_REQ message.  The session key (now shared by the router/PDP
   and the authorizing entity) is used to authenticate the router/PDP,
   and is used to authenticate the authorizing entity.  The session key
   is an encryption key and is also used to encrypt further
   communication between the two parties.  The authorizing entity
   responds by sending a concatenated message of a KRB_AP_REP and a
   KRB_SAFE.  The KRB_AP_REP is used to authenticate the authorizing
   entity.  The KRB_SAFE message contains the authentication data in the
   safe-body field.  The authentication data must be either a 16 byte
   MD5 hash or 20 byte SHA-1 hash of all data in the AUTH_SESSION policy
   element up to the AUTHENTICATION_DATA (note that when using Kerberos
   the AUTH_SESSION PE should not include AUTHENTICATION_DATA as this is
   sent in the KRB_SAFE message).  The router/PDP independently computes
   the hash, and compares it with the received hash in the user-data
   field of the KRB-SAFE-BODY [RFC-1510].

   At a minimum, all AUTH_SESSION implementations using Kerberos MUST
   support the Kerberos des-cbc-md5 encryption type [RFC-1510] (for
   encrypted data in tickets and Kerberos messages) and the Kerberos
   rsa-md5-des checksum type [RFC-1510] (for the KRB_SAFE checksum)
   checksum.  New algorithms may be added by the IETF standards process.
   Triple-DES encryption is supported in many Kerberos implementations
   (although not specified in [RFC-1510]), and SHOULD be used over
   single DES.

   For cases where the authorizing entity is in a different realm (i.e.,
   administrative domain, organizational boundary), the router/PDP needs
   to fetch a cross-realm Ticket Granting Ticket (TGT) from its local
   KDC.  This TGT can be used to fetch authorizing entity tickets from
   the KDC in the remote realm.  Note that for performance
   considerations, tickets are typically cached for extended periods.

4.3 Public Key

   In a public key environment, the AUTH_ENT_ID MUST be of the subtypes:
   X509_V3_CERT or PGP_CERT.  The authentication data is used for
   authenticating the authorizing entity.  An example of the public key
   AUTH_SESSION policy element is shown below.

      +--------------+--------------+--------------+--------------+
      | Length                      | P-type = AUTH_SESSION       |
      +--------------+--------------+--------------+--------------+
      | Length                      |SESSION_ID    |     zero     |
      +--------------+--------------+--------------+--------------+
      | OctetString (The session identifier) ...
      +--------------+--------------+--------------+--------------+
      | Length                      | AUTH_ENT_ID  |   PGP_CERT   |
      +--------------+--------------+--------------+--------------+
      | OctetString (Authorizing entity Digital Certificate) ...
      +--------------+--------------+--------------+--------------+
      | Length                      |AUTH DATA.    |     zero     |
      +--------------+--------------+--------------+--------------+
      | OctetString (Authentication data) ...
      +--------------+--------------+--------------+--------------+

4.3.1. Operational Setting for public key based authentication

      Public key based authentication assumes the following:

      -  Authorizing entities have a pair of keys (private key and
         public key).

      -  Private key is secured with the authorizing entity.

      -  Public keys are stored in digital certificates and a trusted
         party, certificate authority (CA) issues these digital
         certificates.

      -  The verifier (PDP or router) has the ability to verify the
         digital certificate.

   Authorizing entity uses its private key to generate
   AUTHENTICATION_DATA.  Authenticators (router, PDP) use the
   authorizing entity's public key (stored in the digital certificate)
   to verify and authenticate the policy element.

4.3.1.1 X.509 V3 digital certificates

   When the AUTH_ENT_ID is of type X509_V3_CERT, AUTHENTICATION_DATA
   MUST be generated following these steps:

   -  A Signed-data is constructed as defined in section 5 of CMS
      [RFC-3369].  A digest is computed on the content (as specified in
      section 6.1) with a signer-specific message-digest algorithm.  The
      certificates field contains the chain of authorizing entity's
      X.509 V3 digital certificates.  The certificate revocation list is
      defined in the crls field.  The digest output is digitally signed
      following section 8 of RFC 3447, using the signer's private key.

   When the AUTH_ENT_ID is of type X509_V3_CERT, verification MUST be
   done following these steps:

   -  Parse the X.509 V3 certificate to extract the distinguished name
      of the issuer of the certificate.
   -  Certification Path Validation is performed as defined in section 6
      of RFC 3280.
   -  Parse through the Certificate Revocation list to verify that the
      received certificate is not listed.
   -  Once  the X.509 V3 certificate is validated, the public key of the
      authorizing entity can be extracted from the certificate.
   -  Extract the digest algorithm and the length of the digested data
      by parsing the CMS signed-data.
   -  The recipient independently computes the message digest.  This
      message digest and the signer's public key are used to verify the
      signature value.

   This verification ensures integrity, non-repudiation and data origin.

4.3.1.2 PGP digital certificates

   When the AUTH_ENT_ID is of type PGP_CERT, AUTHENTICATION_DATA MUST be
   generated following these steps:

   -  AUTHENTICATION_DATA contains a Signature Packet as defined in
      section 5.2.3 of RFC 2440.  In summary:

      -  Compute the hash of all data in the AUTH_SESSION policy element
         up to the AUTHENTICATION_DATA.
      -  The hash output is digitally signed following section 8 of
         RFC 3447, using the signer's private key.

   When the AUTH_ENT_ID is of type PGP_CERT, verification MUST be done
   following these steps:

   -  Validate the certificate.
   -  Once the PGP certificate is validated, the public key of the
      authorizing entity can be extracted from the certificate.
   -  Extract the hash algorithm and the length of the hashed data by
      parsing the PGP signature packet.
   -  The recipient independently computes the message digest.  This
      message digest and the signer's public key are used to verify the
      signature value.

   This verification ensures integrity, non-repudiation and data origin.

5. Framework

   [RFC-3521] describes a framework in which the AUTH_SESSION policy
   element may be utilized to transport information required for
   authorizing resource reservation for media flows. [RFC-3521]
   introduces 4 different models:

      1- the coupled model
      2- the associated model with one policy server
      3- the associated model with two policy servers
      4- the non-associated model.

   The fields that are required in an AUTH SESSION policy element
   dependent on which of the models is used.

5.1 The coupled model

   In the Coupled Model, the only information that MUST be included in
   the policy element is the SESSION_ID; it is used by the Authorizing
   Entity to correlate the resource reservation request with the media
   authorized during session set up.  Since the End Host is assumed to
   be untrusted, the Policy Server SHOULD take measures to ensure that
   the integrity of the SESSION_ID is preserved in transit; the exact
   mechanisms to be used and the format of the SESSION_ID are
   implementation dependent.

5.2 The associated model with one policy server

   In this model, the contents of the AUTH_SESSION policy element MUST
   include:

   -  A session identifier - SESSION_ID.  This is information that the
      authorizing entity can use to correlate the resource reservation
      request with the media authorized during session set up.

   -  The identity of the authorizing entity - AUTH_ENT_ID.  This
      information is used by the Edge Router to determine which
      authorizing entity (Policy Server) should be used to solicit
      resource policy decisions.

   In some environments, an Edge Router may have no means for
   determining if the identity refers to a legitimate Policy Server
   within its domain.  In order to protect against redirection of
   authorization requests to a bogus authorizing entity, the
   AUTH_SESSION MUST also include:

   -  AUTHENTICATION_DATA.  This authentication data is calculated over
      all other fields of the AUTH_SESSION policy element.

5.3 The associated model with two policy servers

   The content of the AUTH_SESSION Policy Element is identical to the
   associated model with one policy server.

5.4 The non-associated model

   In this model, the AUTH_SESSION MUST contain sufficient information
   to allow the Policy Server to make resource policy decisions
   autonomously from the authorizing entity.  The policy element is
   created using information about the session by the authorizing
   entity.  The information in the AUTH_SESSION policy element MUST
   include:

   -  Calling party IP address or Identity (e.g., FQDN) - SOURCE_ADDR
      X-TYPE
   -  Called party IP address or Identity (e.g., FQDN) - DEST_ADDR
      X-TYPE
   -  The characteristics of (each of) the media stream(s) authorized
      for this session - RESOURCES X-TYPE
   -  The authorization lifetime - START_TIME X-TYPE
   -  The identity of the authorizing entity to allow for validation of
      the token in shared symmetric key and Kerberos schemes -
      AUTH_ENT_ID X-TYPE
   -  The credentials of the authorizing entity in a public-key
      scheme - AUTH_ENT_ID X-TYPE
   -  Authentication data used to prevent tampering with the
      AUTH_SESSION policy element - AUTHENTICATION_DATA

   Furthermore, the AUTH_SESSION policy element MAY contain:

   -  The lifetime of (each of) the media stream(s) - END_TIME X-TYPE
   -  Calling party port number - SOURCE_ADDR X-TYPE
   -  Called party port number - DEST_ADDR X-TYPE

   All AUTH_SESSION fields MUST match with the resource request.  If a
   field does not match, the request SHOULD be denied.

6. Message Processing Rules

6.1 Generation of the AUTH_SESSION by the authorizing entity

   1. Generate the AUTH_SESSION policy element with the appropriate
      contents as specified in section 5.

   2. If authentication is needed, the entire AUTH_SESSION policy
      element is constructed, excluding the length, type and subtype
      fields of the AUTH_SESSION field.  Note that the message MUST
      include either a START_TIME or a SESSION_ID (See Section 9), to
      prevent replay attacks.  The output of the authentication
      algorithm, plus appropriate header information, is appended to the
      AUTH_SESSION policy element.

6.2 Message Generation (RSVP Host)

   An RSVP message is created as specified in [RFC-2205] with the
   following modifications.

   1. RSVP message MUST contain at most one AUTH_SESSION policy element.

   2. The AUTH SESSION policy element received from the authorizing
      entity (Section 3.2) MUST be copied without modification into the
      POLICY DATA object.

   3. POLICY_DATA object (containing the AUTH_SESSION policy element) is
      inserted in the RSVP message in the appropriate place.

6.3 Message Reception (RSVP-aware Router)

   RSVP message is processed as specified in [RFC-2205] with following
   modifications.

   1. If router is policy aware then it SHOULD send the RSVP message to
      the PDP and wait for response.  If the router is policy unaware
      then it ignores the policy data objects and continues processing
      the RSVP message.

   2. Reject the message if the response from the PDP is negative.

   3. Continue processing the RSVP message.

6.4 Authorization (Router/PDP)

   1. Retrieve the AUTH_SESSION policy element.  Check the PE type field
      and return an error if the identity type is not supported.

   2. Verify the message integrity.

      -  Shared symmetric key authentication: The Network router/PDP
         uses the AUTH_ENT_ID field to consult a table keyed by that
         field.  The table should identify the cryptographic
         authentication algorithm to be used along with the expected
         length of the authentication data and the shared symmetric key
         for the authorizing entity.  Verify that the indicated length
         of the authentication data is consistent with the configured
         table entry and validate the authentication data.

      -  Public Key: Validate the certificate chain against the trusted
         Certificate Authority (CA) and validate the message signature
         using the public key.

      -  Kerberos Ticket: If the AUTH_ENT_ID is of subtype
         KRB_PRINCIPAL, Request a ticket for the authorizing entity
         (principal@realm) from the local KDC.  Use the ticket to access
         the authorizing entity and obtain authentication data for the
         message.

   3. Once the identity of the authorizing entity and the validity of
      the service request has been established, the authorizing
      router/PDP MUST then consult its local policy tables (the contents
      of which are a local matter) in order to determine whether or not
      the specific request is authorized.  To the extent to which these
      access control decisions require supplementary information,
      routers/PDPs MUST ensure that supplementary information is
      obtained securely.  An example of insecure access control
      decisions would be if the authorizing party relies upon an
      insecure database (such as DNS or a public LDAP directory) and
      authorizes with a certificate or an FQDN.

   4. Verify the requested resources do not exceed the authorized QoS.

7. Error Signaling

   If a PDP fails to verify the AUTH_SESSION policy element then it MUST
   return a policy control failure (Error Code = 02) to the PEP.  The
   error values are described in [RFC-2205] and [RFC-2750].  Also the
   PDP SHOULD supply a policy data object containing an AUTH_DATA Policy
   Element with A-Type=POLICY_ERROR_CODE containing more details on the
   Policy Control failure [RFC-3182].  If RSVP is being used, the PEP
   MUST include this Policy Data object in the outgoing RSVP Error
   message.

8. IANA Considerations

   Following the policies outlined in [IANA-CONSIDERATIONS], Standard
   RSVP Policy Elements (P-type values) are assigned by IETF Consensus
   action as described in [RFC-2750].

   P-Type AUTH_SESSION is assigned the value 0x04.

   Following the policies outlined in [IANA-CONSIDERATIONS], session
   authorization attribute types (X-Type)in the range 0-127 are
   allocated through an IETF Consensus action; X-Type values between
   128-255 are reserved for Private Use and are not assigned by IANA.

   X-Type AUTH_ENT_ID is assigned the value 1.
   X-Type SESSION_ID is assigned the value 2.
   X-Type SOURCE_ADDR is assigned the value 3.
   X-Type DEST_ADDR is assigned the value 4.
   X-Type START_TIME is assigned the value 5.
   X-Type END_TIME is assigned the value 6.
   X-Type RESOURCES is assigned the value 7.
   X-Type AUTHENTICATION_DATA is assigned the value 8.

   Following the policies outlined in [IANA-CONSIDERATIONS],
   AUTH_ENT_ID SubType values in the range 0-127 are allocated through
   an IETF Consensus action; SubType values between 128-255 are
   reserved for Private Use and are not assigned by IANA.

   AUTH_ENT_ID SubType IPV4_ADDRESS is assigned the value 1.
   SubType IPV6_ADDRESS is assigned the value 2.
   SubType FQDN is assigned the value 3.
   SubType ASCII_DN is assigned the value 4.
   SubType UNICODE_DN is assigned the value 5.
   SubType URI is assigned the value 6.
   SubType KRB_PRINCIPAL is assigned the value 7.
   SubType X509_V3_CERT is assigned the value 8.
   SubType PGP_CERT is assigned the value 9.

   Following the policies outlined in [IANA-CONSIDERATIONS],
   SOURCE_ADDR SubType values in the range 0-127 are allocated through
   an IETF Consensus action; SubType values between 128-255 are
   reserved for Private Use and are not assigned by IANA.

   SOURCE_ADDR SubType IPV4_ADDRESS is assigned the value 1.
   SubType IPV6_ADDRESS is assigned the value 2.
   SubType UDP_PORT_LIST is assigned the value 3.
   SubType TCP_PORT_LIST is assigned the value 4.

   Following the policies outlined in [IANA-CONSIDERATIONS],
   DEST_ADDR SubType values in the range 0-127 are allocated through an
   IETF Consensus action; SubType values between 128-255 are reserved
   for Private Use and are not assigned by IANA.

   DEST_ADDR SubType IPV4_ADDRESS is assigned the value 1.
   SubType IPV6_ADDRESS is assigned the value 2.
   SubType UDP_PORT_LIST is assigned the value 3.
   SubType TCP_PORT_LIST is assigned the value 4.

   Following the policies outlined in [IANA-CONSIDERATIONS],
   START_TIME SubType values in the range 0-127 are allocated through an
   IETF Consensus action; SubType values between 128-255 are
   reserved for Private Use and are not assigned by IANA.

   START_TIME SubType NTP_TIMESTAMP is assigned the value 1.

   Following the policies outlined in [IANA-CONSIDERATIONS],
   END_TIME SubType values in the range 0-127 are allocated through an
   IETF Consensus action; SubType values between 128-255 are reserved
   for Private Use and are not assigned by IANA.

   END_TIME SubType NTP_TIMESTAMP is assigned the value 1.

   Following the policies outlined in [IANA-CONSIDERATIONS],
   RESOURCES SubType values in the range 0-127 are allocated through an
   IETF Consensus action; SubType values between 128-255 are reserved
   for Private Use and are not assigned by IANA.

   RESOURCES SubType BANDWIDTH is assigned the value 1.
   SubType FLOW_SPEC is assigned the value 2.
   SubType SDP is assigned the value 3.
   SubType DSCP is assigned the value 4.

9. Security Considerations

   The purpose of this document is to describe a mechanism for session
   authorization to prevent theft of service.

   Replay attacks MUST be prevented.  In the non-associated model, the
   AUTH_SESSION policy element MUST include a START_TIME field and the
   Policy Servers MUST support NTP to ensure proper clock
   synchronization.  Failure to ensure proper clock synchronization will
   allow replay attacks since the clocks of the different network
   entities may not be in-synch.  The start time is used to verify that
   the request is not being replayed at a later time.  In all other
   models, the SESSION_ID is used by the Policy Server to ensure that
   the resource request successfully correlates with records of an
   authorized session.  If a AUTH_SESSION is replayed, it MUST be
   detected by the policy server (using internal algorithms) and the
   request MUST be rejected.

   To ensure that the integrity of the policy element is preserved in
   untrusted environments, the AUTHENTICATION_DATA attribute MUST be
   included.

   In environments where shared symmetric keys are possible, they should
   be used in order to keep the AUTH_SESSION policy element size to a
   strict minimum.  This is especially true in wireless environments
   where the AUTH_SESSION policy element is sent
   over-the-air.  The shared symmetric keys authentication option MUST
   be supported by all AUTH_SESSION implementations.

   If shared symmetric keys are not a valid option, the Kerberos
   authentication mechanism is reasonably well secured and efficient in
   terms of AUTH_SESSION size.  The AUTH_SESSION only needs to contain
   the principal@realm name of the authorizing entity.  This is much
   more efficient than the PKI authentication option.

   PKI authentication option provides a high level of security and good
   scalability, however it requires the presence of credentials in the
   AUTH_SESSION policy element which impacts its size.

10.  Acknowledgments

   We would like to thank Francois Audet, Don Wade, Hamid Syed, Kwok Ho
   Chan and many others for their valuable comments.  Special thanks to
   Eric Rescorla who provided numerous comments and suggestions that
   improved this document.

   In addition, we would like to thank S. Yadav, et al., for their
   efforts on RFC 3182, as this document borrows from their work.

11.  Normative References

   [ASCII]               Coded Character Set -- 7-Bit American Standard
                         Code for Information Interchange, ANSI X3.4-
                         1986.

   [X.509-ITU]           ITU-T (formerly CCITT) Information technology
                         Open Systems Interconnection - The Directory:
                         Authentication Framework Recommendation X.509
                         ISO/IEC 9594-8

   [RFC-1034]            Mockapetris, P., "Domain names - concepts and
                         facilities", STD 13, RFC 1034, November 1987.

   [RFC-1305]            Mills, D., "Network Time Protocol (Version 3)
                         Specification, Implementation, and Analysis",
                         RFC 1305, March 1992.

   [RFC-1321]            Rivest, R., "The MD5 Message-Digest Algorithm",
                         RFC 1321, April 1992.

   [RFC-1510]            Kohl, J. and C. Neuman, "The Kerberos Network
                         Authentication Service (V5)", RFC 1510,
                         September 1993.

   [RFC-2104]            Krawczyk, H., Bellare, M. and R. Canetti,
                         "HMAC: Keyed-Hashing for Message
                         Authentication", RFC 2104, February 1997.

   [RFC-2119]            Bradner, S., "Key words for use in RFCs to
                         Indicate Requirement Levels", BCP 14, RFC 2119,
                         March 1997.

   [RFC-2205]            Braden, R., Ed., Zhang, L., Berson, S., Herzog,
                         S. and S. Jamin, "Resource ReSerVation Protocol
                         (RSVP) - Version 1 Functional Specification",
                         RFC 2205, September 1997.

   [RFC-2209]            Braden, R. and L. Zhang, "Resource ReSerVation
                         Protocol (RSVP) - Version 1 Message Processing
                         Rules", RFC 2209, September 1997.

   [RFC-2253]            Wahl, M., Kille, S. and T. Howes , "UTF-8
                         String Representation of Distinguished Names",
                         RFC 2253, December 1997.

   [RFC-2279]            Yergeau, F., "UTF-8, a transformation format of
                         ISO 10646", RFC 2279, January 1998.

   [RFC-2327]            Handley, M. and V. Jacobson, "SDP: Session
                         Description Protocol", RFC 2327, October 1998.

   [RFC-2396]            Berners-Lee, T., Fielding, R., Masinter, L.,
                         "Uniform Resource Identifiers (URI): Generic
                         Syntax", RFC 2396, August 1998.

   [RFC-2440]            Callas, J., Donnerhacke, L., Finney, H. and R.
                         Thayer, "OpenPGP Message Format", RFC 2440,
                         November 1998.

   [RFC-2474]            Nichols, K., Blake, S., Baker, F. and D. Black,
                         "Definition of the Differentiated Services
                         Field (DS Field) in the IPv4 and IPv6 Headers",
                         RFC 2474, December 1998.

   [RFC-2750]            Herzog, S., "RSVP Extensions for Policy
                         Control", RFC 2750, January 2000.

   [RFC-2753]            Yavatkar, R., Pendarakis, D. and R. Guerin, "A
                         Framework for Policy-based Admission Control
                         RSVP", RFC 2753, January 2000.

   [RFC-3182]            Yadav, S., Yavatkar, R., Pabbati, R., Ford, P.,
                         Moore, T., Herzog, S. and R. Hess, "Identity
                         Representation for RSVP", RFC 3182, October
                         2001

   [RFC-3280]            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.

   [RFC-3369]            Housley, R., "Cryptographic Message Syntax",
                         RFC 3369, August 2002.

   [RFC-3447]            Jonsson, J. and B. Kaliski, "Public-Key
                         Cryptography Standards (PKCS) #1: RSA
                         Cryptography Specifications Version 2.1", RFC
                         3447, February 2003.

   [RFC-3521]            Hamer, L.-N., Gage, B. and H. Shieh, "Framework
                         for Session Setup with Media Authorization",
                         RFC 3521, April 2003.

12.  Informative References

   [IANA-CONSIDERATIONS] Alvestrand, H. and T. Narten, "Guidelines for
                         Writing an IANA Considerations Section in
                         RFCs", BCP 26, RFC 2434, October 1998.

   [RFC-3261]            Rosenberg, J., Schulzrinne, H., Camarillo, G.,
                         Johnston, A., Peterson, J., Sparks, R.,
                         Handley, M. and E. Schooler, "SIP: Session
                         Initiation Protocol", RFC 3261, June 2002.

13.  Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property 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; neither does it represent that it
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14.  Contributors

   Matt Broda
   Nortel Networks

   EMail: mbroda@nortelnetworks.com

   Louis LeVay
   Nortel Networks

   EMail: levay@nortelnetworks.com

   Dennis Beard
   Nortel Networks

   EMail: beardd@nortelnetworks.com

   Lawrence Dobranski
   Nortel Networks

   EMail: ldobran@nortelnetworks.com

15.  Authors' Addresses

   Louis-Nicolas Hamer
   Nortel Networks
   PO Box 3511 Station C
   Ottawa, Ontario
   Canada K1Y 4H7

   Phone: +1 613.768.3409
   EMail: nhamer@nortelnetworks.com

   Brett Kosinski
   Invidi Technologies
   Edmonton, Alberta
   Canada T5J 3S4

   EMail: brettk@invidi.com

   Bill Gage
   Nortel Networks
   PO Box 3511 Station C
   Ottawa, Ontario
   Canada K1Y 4H7

   Phone: +1 613.763.4400
   EMail: gageb@nortelnetworks.com

   Hugh Shieh
   AT&T Wireless
   7277 164th Avenue NE
   Redmond, WA
   USA 98073-9761

   Phone: +1 425.580.6898
   EMail: hugh.shieh@attws.com

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   Internet Society.

 

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