MSEC Working Group B. Weis
Internet-Draft S. Rowles
Intended status: Standards Track Cisco Systems
Expires: January 8, 2009 July 7, 2008
GDOI Generic Message Authentication Code Policy
draft-weis-gdoi-mac-tek-00
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Abstract
A number of IETF signaling and routing applications require a set of
devices to share the same policy and keying material and include a
message authentication code in their protocols packets for
authentication . It is often beneficial for this keying material to
be chosen dynamically using a group key management protocol. This
memo describes the policy required for the Group Domain of
Interpretation (GDOI) group key management system to distribute a
message authentication code key and associated policy.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements notation . . . . . . . . . . . . . . . . . . 4
2. GDOI Discussion . . . . . . . . . . . . . . . . . . . . . . . 5
3. New GDOI Payload Definitions . . . . . . . . . . . . . . . . . 6
3.1. Message Authentication Code Policy SA TEK . . . . . . . . 6
3.1.1. Application Types . . . . . . . . . . . . . . . . . . 7
3.1.2. MAC Algorithm Types . . . . . . . . . . . . . . . . . 8
3.1.3. Anti-Replay Types . . . . . . . . . . . . . . . . . . 8
3.1.4. Application-Specific Policy Attributes . . . . . . . . 8
3.2. Key Packet definition for MACs . . . . . . . . . . . . . . 8
4. RSVP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. RSVP SA TEK Policy . . . . . . . . . . . . . . . . . . . . 10
4.2. Anti-Replay Discussion . . . . . . . . . . . . . . . . . . 10
4.3. Application-specific attributes . . . . . . . . . . . . . 11
5. NLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. NLS SA TEK Policy . . . . . . . . . . . . . . . . . . . . 12
5.2. Application-specific attributes . . . . . . . . . . . . . 12
6. Requirements for adding additional application support . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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Intellectual Property and Copyright Statements . . . . . . . . . . 20
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1. Introduction
The Group Domain of Interpretation (GDOI) [RFC3547] is a group key
management protocol fitting into the Multicast Security Group Key
Management Architecture [RFC3740]. GDOI is used to disseminate group
security policy and keying material to group members for use with a
particular cryptographic system. RFC 3547 describes the distribution
of group security policy and keying material for IPsec applications,
however group security policy and keying material for other types of
cryptographic systems can also be distributed by GDOI as well.
A number of transport and routing protocol specifications specify a
MAC to provide packet authentication between devices. When the
protocol instantiation includes a group of devices, they all need to
share a common set of authentication policy and keying material to
create and validate the Message Authentication Code (MAC) included in
protocol packets. The requirements for each of the protocol
specifications are generally similar. This document describes how
GDOI can be used to distribute the group authentication policy and
keying material for these protocols.
This memo refers to candidate protocol specifications as
"applications" of the GDOI Generic Message Authentication Code
Policy. Policy distribution for two applications is described:
Resource reSerVation Protocol (RSVP) and Network Layer Signaling
(NLS).
1.1. Scope
This memo is intended to provide policy for applications not
specifying the use of IPsec ESP or AH for authentication. Such
applications SHOULD use the relevant payload definitions described in
RFC 3547. Group applications requiring the use of encryption MUST
NOT use payloads described in this memo, and are encouraged to use
IPsec ESP.
1.2. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. GDOI Discussion
This section provides a short informative discussion of the GDOI
group key management protocol. For definitive information regarding
the GDOI protocol, please refer to RFC 3547. For more information on
group security, please refer to RFC 3740.
The GDOI group key management protocol actively manages security
policy and keying material for a set of group members. GDOI begins
operation when a client application on the group member initiates a
request to the GDOI subsystem on the group member. The GDOI
subsystem "registers" to a GDOI Group Controller/Key Server (GCKS)
device using the GROUPKEY_PULL protocol. The group member and GCKS
setup a private and authenticated exchange. After successful
authentication and authorization, the GCKS provides group security
policy and keying material to the GDOI subsystem on the group member.
When the GDOI subsystem on the group member receives both security
policy and keying material, it makes it available to the client
application on the device that originally requested the MAC policy.
The GDOI key server also distributes policy and keys that describe
how it will distribute updates to group policy over time. Described
in RFC 3547 as the GROUPKEY_PUSH message, it is more generally known
as a "rekey" message. Rekey messages are typically distributed as IP
multicast packets. They provide replacement security policy and
keying material to group members (e.g., prior to a key expiration) or
to revoke group members in a manner that is non-disruptive to the
extant group members.
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3. New GDOI Payload Definitions
The following sections describe how the GDOI Generic Message
Authentication Code Policy is applied to GDOI protocol payloads.
There are two affected payloads: the Security Association (SA)
payload and the Key Download (KD) payload.
The GDOI SA payload includes a set of SA attribute payloads,
including an SA attribute payload which distributes a definition of
the traffic to be secured. This payload is known as the SA TEK.
This memo describes a new type of SA TEK for distributing GDOI
Generic Message Authentication Code Policy. For more information on
the SA TEK attribute payload, please refer to Section 5.4 of RFC
3547.
The GDOI KD payload carries keying material associated with policy
previously distributed in SA attribute payloads. This memo does not
define any new types of key policy for the Message Authentication
Protocol Policy, but does place restrictions on the types of keys
that can be distributed.
3.1. Message Authentication Code Policy SA TEK
This section describes the SA TEK payload used to distribute MAC
policy. Protocols that use a MAC typically define a limited number
of policy attributes associated with the MAC. These policy
attributes are described in the MAC SA TEK.
The GDOI subsystem on a group member must maintain separation between
client applications, and as such needs to know what application
requested a particular set of policy. Thus, the SA TEK includes an
Application field naming the correct application with the group
member. In some instances, client applications define additional
policy, and this policy is described in a set of application-specific
policy attributes attached to the SA TEK.
A GDOI key server may distribute more than on SA TEK for a particular
Application. In particular, the Application-Specific Policy
Attributes may describe discrete instances of an application.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Application | MAC Algorithm ! Anti-Replay !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Key Lifetime !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! SPI Size ! SPI ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Application-Specific Policy Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SA TEK Payload fields are defined as follows:
o Application (2 octets -- Value describing the client application.
Application types are defined below. Values are defined in the
IANA Considerations section.
o MAC Algorithm (1 octet) -- Value specifying which Message
Authentication Code (MAC) used to generate MAC. MAC Algorithm
types are defined below. Values are defined in the IANA
Considerations section.
o Anti-Replay (1 octet) -- Value specifying the type of anti-replay
protection that is used with this application. Anti-replay types
are defined below. Values are defined in the IANA Considerations
section.
o Key Lifetime (4 octets) -- Value specifying the remaining lifetime
of the SA TEK, in seconds. A time of zero indicates that the use
of this policy does not terminate based on time.
o SPI Size (1 octet) -- Length (in octets) of the SPI associated
with this SA TEK.
o SPI (Variable) -- Value describing the identity of the key. The
key identifier uniquely defines an SA TEK.
o Application-Specific Policy Attributes (Variable) -- TLV policy
attributes specific to this application. These attributes are
defined by client application-specific policy.
3.1.1. Application Types
The following Client Applications are defined for use with the MAC SA
TEK.
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o RSVP. The Resource reSerVation Protocol [RFC3097]
o NLS. Network Layer Signaling protocol [I-D.shore-nls-tl]
Other protocols may be defined for use with the Generic Message
Authentication Code Policy SA TEK. However, they must first satisfy
the requirements described in Section 4.
3.1.2. MAC Algorithm Types
The following MAC algorithms are defined for use with this TEK.
o HMAC-MD5. The MD5 algorithm used with an HMAC construction
[RFC2104]. This MAC algorithm is considered weak, but is required
by some protocols.
o HMAC-SHA1-96. The SHA1 algorithm used with an HMAC construction,
with a length truncated to 96 bits.[RFC2104].
3.1.3. Anti-Replay Types
The following methods of constructing sequence numbers is defined for
use with this TEK.
o NONE. This value indicates that no anti-replay protection is used
with this TEK.
o COUNTER. Counters (also known as sequence numbers) provide anti-
replay protection in an application-specific manner.
o TIME. Values from a clock are used for replay protection in an
application-specific manner.
3.1.4. Application-Specific Policy Attributes
Application-Specific Attributes are defined for each application that
requires them. The attributes must follow the format defined in
ISAKMP [RFC2408] Section 3.3. In the table, attributes that are
defined as TV are marked as Basic (B); attributes that are defined as
TLV are marked as Variable (V). Values are defined in the IANA
Considerations section.
3.2. Key Packet definition for MACs
Keying material is distributed in a Key Packet as part of the GDOI KD
payload. The Key packet is formed as follows.
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o KD Type. The type of KD MUST be TEK.
o SPI. The SPI from the SA TEK is placed in the SPI field.
o Key. The keying material for the MAC algorithm is placed in a
TEK_INTEGRITY_KEY attribute.
The Key Packet MUST NOT contain a TEK_ALGORITHM_KEY or
TEK_SOURCE_AUTH_KEY attribute.
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4. RSVP
The RSVP protocol provides a means for establishing resource
reservations between cooperating systems. To ensure the integrity of
the associated reservation and admission control mechanisms, the RSVP
INTEGRITY Option defined in [RFC2747] and [RFC3097] may be used.
These protect RSVP message integrity hop-by-hop and provide node
authentication as well as replay protection, thereby protecting
against corruption and spoofing of RSVP messages. In some network
configurations, a group of cooperating devices exchange RSVP packets
such that the sender of an RSVP packet cannot determine a priori
which RSVP device will be receiving it. These cooperating devices
can benefit from sharing the same group policy and keying material.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] presents a framework for
RSVP security using dynamic group keying and discusses its
applicability. In line with this framework, this section describes
extensions to GDOI for distribution of security policy and keying
material for RSVP.
4.1. RSVP SA TEK Policy
The following describes how the RSVP Integrity object policy is
represented in the MAC SA TEK payload.
o MAC Algorithm. This field maps to the Keyed Message Digest field
of the RFC 2747 INTEGRITY Object. Supported algorithms are: HMAC-
MD5 and HMAC-SHA1-96.
o Anti-Replay. COUNTER and TIME types are both valid types of anti-
replay protection. See a discussion of how they are used below.
o Key Lifetime. If the KeyStartValid optional attribute is included
in the SA TEK, this lifetime specifies the entire lifetime of the
SA TEK. Otherwise, it represents the partial remaining lifetime.
o SPI. This field matches the Key Identifier in the RFC 2747
INTEGRITY Object, and
o SPI Size. The length of the SPI MUST be 1 to 6 octets.
4.2. Anti-Replay Discussion
COUNTER corresponds to the Simple Sequence Numbers method defined in
Section 3.1 of RFC 2747. When COUNTER based sequence numbers are
used, each group member maintains its own sequence number for a given
group in order to set the sequence number field in RSVP messages
generated in this group. Therefore, an RSVP receiver MUST track
received sequence numbers separately for each RSVP neighbour in order
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to reliably distinguish between new and replay messages.
TIME corresponds to the Sequence Numbers Based on a Real Time Clock
method described in Section 3.2 of RFC 2747 or the Sequence Numbers
Based on a Network Recovered Clock method described in Section 3.3 or
RFC 2747.
4.3. Application-specific attributes
o KeyStartValid (V). This attribute specifies an real time in the
future when the TEK will take effect [RFC2747]. Note that the
corresponding KeyEndValid time defined in RFC 2747 is not
distributed by GDOI, but is computed by adding the Key Lifetime
value to KeyStartValid. The KeyStartValid value is represented as
the number of seconds since 0 hours, 0 minutes, 0 seconds, January
1, 1970.
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5. NLS
NLS [I-D.shore-nls-tl] is a core protocol for a generalized on-path
request protocol that is being used today to carry topology discovery
and other requests. NLS specifies the use of group security, where
group members share a MAC key. A MAC result is carried in the NLS
A_RESPONSE and B_RESPONSE TLVs, which consummate authenticated nonce
exchanges. A MAC result is also carried in the NLS AUTHENTICATION
TLV, which is used to ensure integrity of NLS messages. This TLV
also includes a Sequence Number for anti-replay protection. NLS
associates a set of Application Group IDs (AGIDs) with a particular
MAC key. Each AGID represents a unique authorization, within the
context of a particular NLS group.
5.1. NLS SA TEK Policy
The following describes how NLS policy is represented in the MAC SA
TEK payload.
o MAC Algorithm. This field maps to the Keyed Message Digest field
of the RFC 2747 INTEGRITY Object. Supported algorithms are: HMAC-
SHA1-96.
o Anti-Replay. The COUNTER type of anti-replay protection is
supported.
o Key Lifetime. NLS does not specify a validity period for policy.
This field MUST be set to zero.
o SPI. NLS does not specify a key identifier, but this field is
used by GDOI to synchronize policy distributed in an MAC SA TEK
and KD payloads.
o SPI Size. The length of the SPI MUST be 4 octets.
5.2. Application-specific attributes
o AGID (V). This attribute specifies a single NLS AGID that is
associated with this policy. Multiple AGIDs attributes (each
specifying a unique AGID) MAY be included in the SA TEK.
o Authz (V). This attribute contains a token used for
authorization. The format and usage of this authorization token
is outside of the scope of this memo.
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6. Requirements for adding additional application support
Any memo supporting the definitions in the memo MUST include the
following information relating to the application:
o Define an Application Type mnemonic, and provide a reference to a
document describing the protocol specification.
o Define a set of MAC algorithms.
o Define anti-replay types.
o Define key lifetime parameters.
o Define valid SPI values and lengths.
o Description of Optional Attributes.
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7. IANA Considerations
A new GDOI SA TEK type Protocol-ID type [GDOI-REG] should be assigned
from the RESERVED space. The new algorithm id should be called
GDOI_PROTO_RSVP_INTEGRITY, and refers to the INTEGRITY Object defined
in [RFC2747].
Terms describing policies for allocating new name space types below
are defined in [RFC2434].
The following applications are defined as part of this memo.
Application Type Value
------------------ -----
RESERVED 0
RSVP 1
NLS 2
Specification Required 3-127
Private Use 128-255
The following MAC Algorithms are defined as a part of this memo.
MAC Algorithm Type Value
------------------ -----
RESERVED 0
HMAC-MD5 1
HMAC-SHA1-96 2
Specification Required 3-127
Private Use 128-255
The following Sequence Number Types are defined as a part of this
memo.
Sequence Number Type Value
-------------------- -----
RESERVED 0
COUNTER 1
TIME 2
Specification Required 3-127
Private Use 128-255
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The following Optional Attributes are defined as part of this memo,
used with an Application of type RSVP.
RSVP Optional Attribute Value
----------------------- -----
RESERVED 0
KeyStartValid 1
Specification Required 2-127
Private Use 128-255
The following Optional Attributes are defined as part of this memo,
used with an Application of type NLS.
NLS Optional Attribute Value
---------------------- -----
RESERVED 0
AGID 1
Authz 2
Specification Required 3-127
Private Use 128-255
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8. Security Considerations
This memo describes the passing of policy and keying material used by
two applications: an RSVP speaker producing an RFC 2747 INTEGRITY
Object, and an NLS speaker producing A_RESPONSE, B_RESPONSE, and
AUTHENTICATION TLVs. This policy and keying material is protected by
the GDOI protocol described in [RFC3547]. The security
considerations in that memo apply fully to this memo as well.
The use of the MAC SA TEK to distribute policy and keys is only
appropriate when the application is using a group security model.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] describes the
circumstances when a group security model may be used with RSVP. NLS
always uses a group security model.
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9. References
9.1. Normative References
[RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The
Group Domain of Interpretation", RFC 3547, July 2003.
9.2. Informative References
[GDOI-REG]
Internet Assigned Numbers Authority, "Group Domain of
Interpretation (GDOI) Payload Type Values", IANA Registry,
December 2004,
<http://www.iana.org/assignments/gdoi-payloads>.
[I-D.ietf-tsvwg-rsvp-security-groupkeying]
Behringer, M. and F. Faucheur, "Applicability of Keying
Methods for RSVP Security",
draft-ietf-tsvwg-rsvp-security-groupkeying-00 (work in
progress), February 2008.
[I-D.shore-nls-tl]
Shore, M., "Network-Layer Signaling: Transport Layer",
draft-shore-nls-tl-05 (work in progress), June 2007.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2408] Maughan, D., Schneider, M., and M. Schertler, "Internet
Security Association and Key Management Protocol
(ISAKMP)", RFC 2408, November 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, January 2000.
[RFC3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value", RFC 3097,
April 2001.
[RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security
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Architecture", RFC 3740, March 2004.
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Authors' Addresses
Brian Weis
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-526-4796
Email: bew@cisco.com
Sheela Rowles
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-527-7677
Email: srowles@cisco.com
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