RAP Working Group L-N. Hamer
Internet Draft B. Gage
Nortel Networks
Document: draft-ietf-rap-rsvp-authsession-04.txt B. Kosinski
University of Alberta
Hugh Shieh
AT&T Wireless
October 2002
Session Authorization Policy Element
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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The distribution of this memo is unlimited. This memo is filed as
<draft-ietf-rap-rsvp-authsession-04.txt>, and expires March,
2003. Please send comments to the authors.
Copyright Notice
Copyright (C) The Internet Society (2002). 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 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.
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Contents
Status of this Memo................................................1
Copyright Notice...................................................1
Abstract...........................................................1
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.........................14
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.............................16
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)....................................20
7. Error Signaling................................................21
8. IANA Considerations............................................21
9. Security Considerations........................................23
10. Acknowledgments...............................................24
11. Normative References..........................................24
12. Informative References........................................26
13. Author Information............................................26
14. Contributors..................................................27
15. Full Copyright Statement......................................27
16. Notices.......................................................27
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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 [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.
[S-AUTH] 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.
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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 = TBD-by-IANA
The Policy element type (P-type) of this element. The
Internet Assigned Numbers Authority (IANA) acts as a registry
for policy element types for identity 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.
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+--------+--------+--------+--------+
| Length | S-Type |SubType |
+--------+--------+--------+--------+
| Value ...
+--------+--------+--------+--------+
Length: 16 bits
The length field is two octets and indicates the actual length
of the attribute (including Length, S-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.
S-Type: 8 bits
Session authorization attribute type (S-Type) field is one
octet. IANA acts as a registry for S-Types as described
in section 7, IANA Considerations. Initially, the registry
contains the following S-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 S-Type.
Value: variable length
The attribute specific information.
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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 |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
Length
Length of the attribute, which MUST be > 4.
S-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 A chain of authorizing entity's X.509 V3
digital certificates as defined in RFC-
3280.
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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 number or on a standard
NTP timestamp.
+-------+-------+-------+-------+
| Length |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
Length
Length of the attribute, which MUST be > 4.
S-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 S-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 |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
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Internet Draft Session Authorization Policy Element October 2002
Length
Length of the attribute, which MUST be > 4.
S-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 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 UDP_PORT_LIST list of UDP port specifications,
represented as 16 bits per list entry.
7 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 5 (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 when resolved to an IP address.
At most, one instance of subtype 6 MAY be included in every Session
Authorization Data Policy Element. At most, one instance of subtype
7 MAY be included in every Session Authorization Data Policy
Element. Inclusion of a subtype 6 attribute does not prevent
inclusion of a subtype 7 attribute (i.e. both UDP and TCP ports may
be authorized).
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Internet Draft Session Authorization Policy Element October 2002
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 S-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 |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
Length
Length of the attribute, which MUST be > 4.
S-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 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 UDP_PORT_LIST list of UDP port specifications,
represented as 16 bits per list entry.
7 TCP_PORT_LIST list of TCP port specifications,
represented as 16 bits per list entry.
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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 5 (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 when resolved to an IP address.
At most, one instance of subtype 6 MAY be included in every Session
Authorization Data Policy Element. At most, one instance of subtype
7 MAY be included in every Session Authorization Data Policy
Element. Inclusion of a subtype 6 attribute does not prevent
inclusion of a subtype 7 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 |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
Length
Length of the attribute, which MUST be > 4.
S-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:
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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 |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
Length
Length of the attribute, which MUST be > 4.
S-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 S-Type may be useful in some scenarios to specify the
specific resources authorized to ensure the request fits the
authorized specifications.
+-------+-------+-------+-------+
| Length |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
Length
Length of the attribute, which MUST be > 4.
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S-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 |S-Type |SubType|
+-------+-------+-------+-------+
| OctetString ...
+-------+-------+-------+-------+
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Length
Length of the attribute, which MUST be > 4.
S-Type
AUTHENTICATION_DATA
SubType
No sub types for AUTHENTICATION_DATA are currently defined. This
field MUST be set to 0.
OctetString
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_ADDR, IPV6_ADDR, 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 DATA. | zero |
+--------------+--------------+--------------+--------------+
| 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
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field. 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][FRC-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. 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). 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
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"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.
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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 entityÆs 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:
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- 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 digest
output is digitally signed following section 8 of RFC-2437, 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-
2437, using the signer's private key.
When the AUTH_ENT_ID is of type PGP_CERT, verification MUST be done
following these steps:
- Parse the PGP certificate to extract the distinguished name of the
issuer of the certificate.
- Validate the certificate.
- Parse through the Certificate Revocation list to verify that the
received certificate is not listed.
- 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.
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Internet Draft Session Authorization Policy Element October 2002
- 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
[S-AUTH] describes a framework in which the AUTH_SESSION
policy element may be utilized to transport information required for
authorizing resource reservation for media flows. [S-AUTH]
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
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Internet Draft Session Authorization Policy Element October 2002
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 S-
TYPE
- Called party IP address or Identity (e.g. FQDN) - DEST_ADDR S-
TYPE
- The characteristics of (each of) the media stream(s) authorized
for this session - RESOURCES S-TYPE
- The authorization lifetime - START_TIME S-TYPE
- The identity of the authorizing entity to allow for validation of
the token in shared symmetric key and Kerberos schemes -
AUTH_ENT_ID S-TYPE
- The credentials of the authorizing entity in a public-key scheme
- AUTH_ENT_ID S-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 S-TYPE
- Calling party port number - SOURCE_ADDR S-TYPE
- Called party port number - DEST_ADDR S-TYPE
All AUTH_SESSION fields MUST match with the resource request. If a
field does not match, the request SHOULD be denied.
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Internet Draft Session Authorization Policy Element October 2002
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.
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Internet Draft Session Authorization Policy Element October 2002
- 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. 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 TBD-by-IANA.
Following the policies outlined in [IANA-CONSIDERATIONS], session
authorization attribute types (S-Type)in the range 0-127 are
allocated through an IETF Consensus action; S-Type values between
128-255 are reserved for Private Use and are not assigned by IANA.
S-Type AUTH_ENT_ID is assigned the value 1.
S-Type SESSION_ID is assigned the value 2.
S-Type SOURCE_ADDR is assigned the value 3.
S-Type DEST_ADDR is assigned the value 4.
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Internet Draft Session Authorization Policy Element October 2002
S-Type START_TIME is assigned the value 5.
S-Type END_TIME is assigned the value 6.
S-Type RESOURCES is assigned the value 7.
S-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 FQDN is assigned the value 3.
SubType ASCII_DN is assigned the value 4.
SubType UNICODE_DN is assigned the value 5.
SubType UDP_PORT_LIST is assigned the value 6.
SubType TCP_PORT_LIST is assigned the value 7.
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 FQDN is assigned the value 3.
SubType ASCII_DN is assigned the value 4.
SubType UNICODE_DN is assigned the value 5.
SubType UDP_PORT_LIST is assigned the value 6.
SubType TCP_PORT_LIST is assigned the value 7.
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.
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Internet Draft Session Authorization Policy Element October 2002
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 draft 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. 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 order to keep the AUTH_SESSION policy element size to a strict
minimum, in environments where shared symmetric keys are possible,
they should be used. 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
Hamer, et al. [Page 23]
Internet Draft Session Authorization Policy Element October 2002
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.
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
[S-AUTH] Hamer, L.-N., Gage, B., Shieh, H., "Framework
for session setup with media authorization",
Internet-Draft,
draft-ietf-rap-session-auth-04.txt,
June 2002.
[ASCII] Coded Character Set -- 7-Bit American
Standard Code for Information Interchange,
ANSI X3.4-1986.
[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-1034] Mockapetris, P.V., "Domain names - concepts
and facilities", RFC 1034, November 1987.
[RFC-1305] Mills, David L., "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.
Hamer, et al. [Page 24]
Internet Draft Session Authorization Policy Element October 2002
[RFC-2104] Krawczyk, H., Bellare, M. and R. Canetti,
"HMAC: Keyed-Hashing for Message
Authentication", RFC 2104, February 1997.
[RFC-2253] Wahl, M. et al., "UTF-8 String
Representation of Distinguished Names",
RFC 2253, December 1997.
[RFC-2205] Braden, R., 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-2327] Handley, M., Jacobson, V., "SDP: Session
Description Protocol", RFC 2327, October
1998.
[RFC-2396] Berners-Lee, T., Fielding, R., Irvine, U.C.,
Masinter, L., "Uniform Resource Identifiers
(URI): Generic Syntax", RFC 2396, August
1998.
[RFC-2474] Nichols, K., Blake, S., Baker, F., Black, D.,
"Definition of the Differentiated Services
Field (DS Field) in the IPv4 and IPv6
Headers", RFC 2474, December 1998.
[RFC-2279] Yergeau, F., "UTF-8, a transformation format
of ISO 10646", RFC 2279, January 1998.
[RFC-3280] Housley, R., et al., "Internet X.509 Public
Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile",
RFC 3280, April 2002.
[X.509-ITU] ITU-T (formerly CCITT) Information technology
Open Systems Interconnection - The Directory:
Authentication Framework Recommendation X.509
ISO/IEC 9594-8
[RFC-2437] Kaliski, B., Staddon, J., "PKCS #1: RSA
Cryptography Specifications Version 2.0."
RFC 2437, October 1998.
[RFC-3369] Housley, R., "Cryptographic Message Syntax",
RFC 3369, August 2002.
Hamer, et al. [Page 25]
Internet Draft Session Authorization Policy Element October 2002
[RFC-2440] Callas, J., "OpenPGP Message Format", RFC
2440, November 1998.
[RFC-3182] S. Yadav et al., "Identity Representation for
RSVP", RFC 3182, October 2001
12. Informative References
[RFC-3261] Rosenberg et al., "SIP: Session Initiation
Protocol", RFC 3261, June 2002.
[IANA-CONSIDERATIONS] Alvestrand, H. and T. Narten, "Guidelines for
Writing an IANA Considerations Section in
RFCs", BCP 26, RFC 2434, October 1998.
13. Author Information
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
University of Alberta
Edmonton, Alberta
Canada T6G 2M7
EMail: kosinski@cs.ualberta.ca
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
Hamer, et al. [Page 26]
Internet Draft Session Authorization Policy Element October 2002
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. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved. This
document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organisations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into.
16. Notices
"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 has made any effort to identify any such
rights. Information on the IETF's procedures with respect to
rights in standards-track and standards-related documentation
can be found in BCP-11. Copies of claims of rights made
available for publication 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
Hamer, et al. [Page 27]
Internet Draft Session Authorization Policy Element October 2002
proprietary rights by implementors or users of this
specification can be obtained from the IETF Secretariat."
"The IETF invites any interested party to bring to its
attention any copyrights, patents or patent applications, or
other proprietary rights which may cover technology that may be
required to practice this standard. Please address the
information to the IETF Executive Director."
17. RFC Editor Considerations
This document references an IETF Internet-Draft that is in the IESG
last call stage. Please use the corresponding RFC number prior to
publishing of this document as a RFC. The referenced IETF I-D is
[S-AUTH].
Hamer, et al. [Page 28]
