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CVS shishi/doc/specifications |
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Mon, 17 Jan 2005 23:10:06 +0100 |
Update of /home/cvs/shishi/doc/specifications
In directory dopio:/tmp/cvs-serv16467
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draft-zhu-kerb-enctype-nego-00.txt
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NETWORK WORKING GROUP L. Zhu
Internet-Draft P. Leach
Expires: June 4, 2005 K. Jaganathan
Microsoft Corporation
December 2004
Kerberos Cryptosystem Negotiation Extension
draft-zhu-kerb-enctype-nego-00
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 4, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document specifies an extension by Kerberos to negotiate new
encryption types between the client-server peers.
Zhu, et al. Expires June 4, 2005 [Page 1]
Internet-Draft Enctype Negotiation December 2004
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . 4
3. Negotiation Protocol . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
6. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 7
A. Leveraging this Enctype Negotiation in Windows SPNEGO
Implementations . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . 10
Zhu, et al. Expires June 4, 2005 [Page 2]
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1. Introduction
Under the current mechanism [CLAR], the KDC must limit the ticket
session key enctype chosen for a given service to one it believes is
supported by both the client and the server. If both the client and
server understand a stronger enctype than is selected by the KDC,
they can not negotiate it. As the result, the protection of
application traffic is often weaker than necessary when different
application software that support different set of enctypes can be
used by the same server principal.
This document specifies an extension to Kerberos to allow clients and
servers to negotiate a different and possible stronger cryptosystem
to be used in subsequent communication.
This extension utilizes an authorization data element in the
authenticator of the KRB_AP_REQ message [CLAR]. The client sends the
list of enctypes that it supports to the server, the server then
informs the client its choice. The negotiated subkey is sent in the
KRB_AP_REP.
Zhu, et al. Expires June 4, 2005 [Page 3]
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2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Negotiation Protocol
If the client prefers an enctype over that of the service ticket
session key, then it MUST send the list of enctypes it supports
(including the one selected by the KDC), in decreasing preference
order.
The client sends the enctype list via the authorization-data of the
authenticator in the KRB_AP_REQ [CLAR]. A new authorization data
element type AD-ETYPE-NEGOTIATION (129) is defined. This
authorization data element itself is enclosed in the AD-IF-RELEVANT
container, thus a correctly implemented server that does not
understand this element should ignore it [CLAR]. The value of this
authorization element contains the DER [X60] encoding of the
following ASN.1 type:
EtypeList ::= SEQUENCE OF Int32
-- the client's proposed enctype list in decreasing
-- preference order, favorite choice first
If the EtypeList is present and the server prefers an enctype from
the client's enctype list over that of the KRB_AP_REQ authenticator
subkey (if that is present) or the service ticket session key, the
server MUST create a subkey using that enctype. This negotiated
subkey is sent in the subkey field of KRB_AP_REP message and it MUST
be used for subsequent communication.
Note that to preserve the quality of randomness provided by the KDC,
implementations of this protocol SHOULD consider using the service
ticket session key value as a source of additional entropy when
generating the negotiated subkey. If the KRB_AP_REQ authenticator
subkey is present, it MAY also be used as a source of entropy.
The policy by which the client or the server chooses an enctype
(i.e., how the preference order for the supported enctypes is
selected) is an implementation-specific local matter.
Zhu, et al. Expires June 4, 2005 [Page 5]
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4. Security Considerations
The client's enctype list and the server's reply enctype are part of
encrypted data, thus the security considerations are the same as
those of the Kerberos encrypted data.
In all cases, the communicating peers are exposed to the denial of
service threat.
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5. IANA Considerations
No IANA actions are required for this document.
6. Normative References
[CLAR] Neuman, B., Yu, Y., Hartman, S. and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", August
2004.
[GSS-CFX] Zhu, L., Jaganathan, K. and S. Hartman, "The Kerberos
Version 5 GSS-API Mechanism: Version 2", November 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[SPNEGOBIS]
Zhu, L., Leach, P., Jaganathan, K., Hartman, S. and W.
Ingersoll, "The Simple and Protected GSS-API Negotiation
Mechanism", November 2004.
Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: address@hidden
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: address@hidden
Zhu, et al. Expires June 4, 2005 [Page 7]
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Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
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