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doc/standardisation/draft-ietf-krb-wg-crypto-06.txt
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doc/standardisation/draft-ietf-krb-wg-crypto-06.txt
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doc/standardisation/draft-ietf-krb-wg-gssapi-cfx-03.txt
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doc/standardisation/draft-ietf-krb-wg-gssapi-cfx-03.txt
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<Network Working Group> Larry Zhu
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Internet Draft Karthik Jaganathan
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Updates: 1964 Microsoft
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Category: Standards Track Sam Hartman
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draft-ietf-krb-wg-gssapi-cfx-03.txt MIT
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October 26, 2003
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Expires: April 26, 2004
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The Kerberos Version 5 GSS-API Mechanism: Version 2
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Status of this Memo
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This document is an Internet-Draft and is in full conformance with
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all provisions of Section 10 of [RFC-2026].
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Internet-Drafts are working documents of the Internet Engineering
|
||||||
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Task Force (IETF), its areas, and its working groups. Note that
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|
other groups may also distribute working documents as Internet-
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||||||
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Drafts. Internet-Drafts are draft documents valid for a maximum of
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||||||
|
six months and may be updated, replaced, or obsoleted by other
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documents at any time. It is inappropriate to use Internet-Drafts
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as reference material or to cite them other than as "work in
|
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|
progress."
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||||||
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||||||
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The list of current Internet-Drafts can be accessed at
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||||||
|
http://www.ietf.org/ietf/1id-abstracts.txt.
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||||||
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|
||||||
|
The list of Internet-Draft Shadow Directories can be accessed at
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||||||
|
http://www.ietf.org/shadow.html.
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Abstract
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This memo defines protocols, procedures, and conventions to be
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employed by peers implementing the Generic Security Service
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Application Program Interface (GSS-API as specified in [RFC-2743])
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when using the Kerberos Version 5 mechanism (as specified in
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||||||
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[KRBCLAR]).
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[RFC-1964] is updated and incremental changes are proposed in
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|
response to recent developments such as the introduction of Kerberos
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||||||
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crypto framework [KCRYPTO]. These changes support the inclusion of
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||||||
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new cryptosystems based on crypto profiles [KCRYPTO], by defining
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new per-message tokens along with their encryption and checksum
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algorithms.
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Conventions used in this document
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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||||||
|
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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|
document are to be interpreted as described in [RFC-2119].
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1. Introduction
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Zhu Internet Draft 1
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||||||
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Kerberos Version 5 GSS-API October 2003
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||||||
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||||||
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||||||
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[KCRYPTO] defines a generic framework for describing encryption and
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checksum types to be used with the Kerberos protocol and associated
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protocols.
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||||||
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[RFC-1964] describes the GSS-API mechanism for Kerberos Version 5.
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It defines the format of context establishment, per-message and
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|
context deletion tokens and uses algorithm identifiers for each
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cryptosystem in per message and context deletion tokens.
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||||||
|
The approach taken in this document obviates the need for algorithm
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||||||
|
identifiers. This is accomplished by using the same encryption
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|
algorithm, specified by the crypto profile [KCRYPTO] for the session
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||||||
|
key or subkey that is created during context negotiation, and its
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||||||
|
required checksum algorithm. Message layouts of the per-message
|
||||||
|
tokens are therefore revised to remove algorithm indicators and also
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||||||
|
to add extra information to support the generic crypto framework
|
||||||
|
[KCRYPTO].
|
||||||
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|
||||||
|
Tokens transferred between GSS-API peers for security context
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||||||
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establishment are also described in this document. The data
|
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|
elements exchanged between a GSS-API endpoint implementation and the
|
||||||
|
Kerberos KDC are not specific to GSS-API usage and are therefore
|
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defined within [KRBCLAR] rather than within this specification.
|
||||||
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The new token formats specified in this memo MUST be used with all
|
||||||
|
"newer" encryption types [KRBCLAR] and MAY be used with "older"
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||||||
|
encryption types, provided that the initiator and acceptor know,
|
||||||
|
from the context establishment, that they can both process these new
|
||||||
|
token formats.
|
||||||
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|
||||||
|
"Newer" encryption types are those which have been specified along
|
||||||
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with or since the new Kerberos cryptosystem specification [KCRYPTO],
|
||||||
|
as defined in section 3.1.3 of [KRBCLAR].
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||||||
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|
||||||
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Note that in this document, the term "little endian order" is used
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||||||
|
for brevity to refer to the least-significant-octet-first encoding,
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||||||
|
while the term "big endian order" is for the most-significant-octet-
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||||||
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first encoding.
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||||||
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|
||||||
|
2. Key Derivation for Per-Message Tokens
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||||||
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||||||
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To limit the exposure of a given key, [KCRYPTO] adopted "one-way"
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||||||
|
"entropy-preserving" derived keys, for different purposes or key
|
||||||
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usages, from a base key or protocol key. This document defines four
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||||||
|
key usage values below for signing and sealing messages:
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||||||
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Name Value
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||||||
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-------------------------------------
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||||||
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KG-USAGE-ACCEPTOR-SEAL 22
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||||||
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KG-USAGE-ACCEPTOR-SIGN 23
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KG-USAGE-INITIATOR-SEAL 24
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KG-USAGE-INITIATOR-SIGN 25
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Zhu Internet Draft 2
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||||||
|
Kerberos Version 5 GSS-API October 2003
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When the sender is the context acceptor, KG-USAGE-ACCEPTOR-SIGN is
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used as the usage number in the key derivation function for deriving
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keys to be used in MIC tokens, and KG-USAGE-ACCEPTOR-SEAL is used
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for Wrap tokens; similarly when the sender is the context initiator,
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KG-USAGE-INITIATOR-SIGN is used as the usage number in the key
|
||||||
|
derivation function for MIC tokens, KG-USAGE-INITIATOR-SEAL is used
|
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for Wrap Tokens. Even if the Wrap token does not provide for
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||||||
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confidentiality the same usage values specified above are used.
|
||||||
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||||||
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During the context initiation and acceptance sequence, the acceptor
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MAY assert a subkey. If the acceptor asserts a subkey, subsequent
|
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messages SHOULD use this subkey as the protocol key and these
|
||||||
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messages MUST be flagged as "AcceptorSubkey" as described in section
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4.2.2.
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3. Quality of Protection
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||||||
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The GSS-API specification [RFC-2743] provides for Quality of
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||||||
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Protection (QOP) values that can be used by applications to request
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||||||
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a certain type of encryption or signing. A zero QOP value is used
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||||||
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to indicate the "default" protection; applications which do not use
|
||||||
|
the default QOP are not guaranteed to be portable across
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||||||
|
implementations or even inter-operate with different deployment
|
||||||
|
configurations of the same implementation. Using an algorithm that
|
||||||
|
is different from the one for which the key is defined may not be
|
||||||
|
appropriate. Therefore, when the new method in this document is
|
||||||
|
used, the QOP value is ignored.
|
||||||
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|
||||||
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The encryption and checksum algorithms in per-message tokens are now
|
||||||
|
implicitly defined by the algorithms associated with the session key
|
||||||
|
or subkey. Algorithms identifiers as described in [RFC-1964] are
|
||||||
|
therefore no longer needed and removed from the new token headers.
|
||||||
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||||||
|
4. Definitions and Token Formats
|
||||||
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||||||
|
This section provides terms and definitions, as well as descriptions
|
||||||
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for tokens specific to the Kerberos Version 5 GSS-API mechanism.
|
||||||
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|
||||||
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4.1. Context Establishment Tokens
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||||||
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||||||
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All context establishment tokens emitted by the Kerberos V5 GSS-API
|
||||||
|
mechanism will have the framing shown below:
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||||||
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||||||
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GSS-API DEFINITIONS ::=
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||||||
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||||||
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BEGIN
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||||||
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||||||
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MechType ::= OBJECT IDENTIFIER
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||||||
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-- representing Kerberos V5 mechanism
|
||||||
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||||||
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GSSAPI-Token ::=
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||||||
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-- option indication (delegation, etc.) indicated within
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||||||
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-- mechanism-specific token
|
||||||
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[APPLICATION 0] IMPLICIT SEQUENCE {
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||||||
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||||||
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Zhu Internet Draft 3
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||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
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||||||
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||||||
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thisMech MechType,
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||||||
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innerToken ANY DEFINED BY thisMech
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||||||
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-- contents mechanism-specific
|
||||||
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-- ASN.1 structure not required
|
||||||
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}
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||||||
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||||||
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END
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||||||
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||||||
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Where the notation and encoding of this pseudo ASN.1 header, which
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is referred as the generic GSS-API token framing later in this
|
||||||
|
document, are described in [RFC-2743], and the innerToken field
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||||||
|
starts with a two-octet token-identifier (TOK_ID) expressed in big
|
||||||
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endian order, followed by a Kerberos message.
|
||||||
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|
||||||
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Here are the TOK_ID values used in the context establishment tokens:
|
||||||
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|
||||||
|
Token TOK_ID Value in Hex
|
||||||
|
-----------------------------------------
|
||||||
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KRB_AP_REQUEST 01 00
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||||||
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KRB_AP_REPLY 02 00
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||||||
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KRB_ERROR 03 00
|
||||||
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||||||
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Where Kerberos message KRB_AP_REQUEST, KRB_AP_REPLY, and KRB_ERROR
|
||||||
|
are defined in [KRBCLAR].
|
||||||
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||||||
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If an unknown token identifier (TOK_ID) is received in the initial
|
||||||
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context estalishment token, the receiver MUST return
|
||||||
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GSS_S_CONTINUE_NEEDED major status, and the returned output token
|
||||||
|
MUST contain a KRB_ERROR message with the error code
|
||||||
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KRB_AP_ERR_MSG_TYPE [KRBCLAR].
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||||||
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||||||
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4.1.1. Authenticator Checksum
|
||||||
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||||||
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The authenticator in the KRB_AP_REQ message MUST include the
|
||||||
|
optional sequence number and the checksum field. The checksum field
|
||||||
|
is used to convey service flags, channel bindings, and optional
|
||||||
|
delegation information. The checksum type MUST be 0x8003. The
|
||||||
|
length of the checksum MUST be 24 octets when delegation is not
|
||||||
|
used. When delegation is used, a ticket-granting ticket will be
|
||||||
|
transferred in a KRB_CRED message. This ticket SHOULD have its
|
||||||
|
forwardable flag set. The KRB_CRED message MUST be encrypted in the
|
||||||
|
session key of the ticket used to authenticate the context.
|
||||||
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||||||
|
The format of the authenticator checksum field is as follows.
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||||||
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|
||||||
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Octet Name Description
|
||||||
|
-----------------------------------------------------------------
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||||||
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0..3 Lgth Number of octets in Bnd field; Currently
|
||||||
|
contains hex value 10 00 00 00 (16, represented
|
||||||
|
in little-endian order)
|
||||||
|
4..19 Bnd Channel binding information, as described in
|
||||||
|
section 4.1.1.2.
|
||||||
|
20..23 Flags Four-octet context-establishment flags in little-
|
||||||
|
endian order as described in section 4.1.1.1.
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 4
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
24..25 DlgOpt The Delegation Option identifier (=1) [optional]
|
||||||
|
26..27 Dlgth The length of the Deleg field [optional]
|
||||||
|
28..n Deleg A KRB_CRED message (n = Dlgth + 29) [optional]
|
||||||
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|
||||||
|
4.1.1.1. Checksum Flags Field
|
||||||
|
|
||||||
|
The checksum "Flags" field is used to convey service options or
|
||||||
|
extension negotiation information. The following context
|
||||||
|
establishment flags are defined in [RFC-2744].
|
||||||
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|
||||||
|
Flag Name Value
|
||||||
|
---------------------------------
|
||||||
|
GSS_C_DELEG_FLAG 1
|
||||||
|
GSS_C_MUTUAL_FLAG 2
|
||||||
|
GSS_C_REPLAY_FLAG 4
|
||||||
|
GSS_C_SEQUENCE_FLAG 8
|
||||||
|
GSS_C_CONF_FLAG 16
|
||||||
|
GSS_C_INTEG_FLAG 32
|
||||||
|
|
||||||
|
Context establishment flags are exposed to the calling application.
|
||||||
|
If the calling application desires a particular service option then
|
||||||
|
it requests that option via GSS_Init_sec_context() [RFC-2743]. An
|
||||||
|
implementation that supports a particular option or extension SHOULD
|
||||||
|
then set the appropriate flag in the checksum Flags field.
|
||||||
|
|
||||||
|
The most significant eight bits of the checksum flags are reserved
|
||||||
|
for future use. The receiver MUST ignore unknown checksum flags.
|
||||||
|
|
||||||
|
4.1.1.2. Channel Binding Information
|
||||||
|
|
||||||
|
Channel bindings are user-specified tags to identify a given context
|
||||||
|
to the peer application. These tags are intended to be used to
|
||||||
|
identify the particular communications channel that carries the
|
||||||
|
context [RFC-2743] [RFC-2744].
|
||||||
|
|
||||||
|
When using C language bindings, channel bindings are communicated to
|
||||||
|
the GSS-API using the following structure [RFC-2744]:
|
||||||
|
|
||||||
|
typedef struct gss_channel_bindings_struct {
|
||||||
|
OM_uint32 initiator_addrtype;
|
||||||
|
gss_buffer_desc initiator_address;
|
||||||
|
OM_uint32 acceptor_addrtype;
|
||||||
|
gss_buffer_desc acceptor_address;
|
||||||
|
gss_buffer_desc application_data;
|
||||||
|
} *gss_channel_bindings_t;
|
||||||
|
|
||||||
|
The member fields and constants used for different address types are
|
||||||
|
defined in [RFC-2744].
|
||||||
|
|
||||||
|
The "Bnd" field contains the MD5 hash of channel bindings, taken
|
||||||
|
over all non-null components of bindings, in order of declaration.
|
||||||
|
Integer fields within channel bindings are represented in little-
|
||||||
|
endian order for the purposes of the MD5 calculation.
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 5
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
In computing the contents of the Bnd field, the following detailed
|
||||||
|
points apply:
|
||||||
|
|
||||||
|
(1) Each integer field shall be formatted into four octets, using
|
||||||
|
little endian octet ordering, for purposes of MD5 hash computation.
|
||||||
|
|
||||||
|
(2) All input length fields within gss_buffer_desc elements of a
|
||||||
|
gss_channel_bindings_struct even those which are zero-valued, shall
|
||||||
|
be included in the hash calculation; the value elements of
|
||||||
|
gss_buffer_desc elements shall be dereferenced, and the resulting
|
||||||
|
data shall be included within the hash computation, only for the
|
||||||
|
case of gss_buffer_desc elements having non-zero length specifiers.
|
||||||
|
|
||||||
|
(3) If the caller passes the value GSS_C_NO_BINDINGS instead of a
|
||||||
|
valid channel binding structure, the Bnd field shall be set to 16
|
||||||
|
zero-valued octets.
|
||||||
|
|
||||||
|
4.2. Per-Message Tokens
|
||||||
|
|
||||||
|
Two classes of tokens are defined in this section: "MIC" tokens,
|
||||||
|
emitted by calls to GSS_GetMIC() and consumed by calls to
|
||||||
|
GSS_VerifyMIC(), "Wrap" tokens, emitted by calls to GSS_Wrap() and
|
||||||
|
consumed by calls to GSS_Unwrap().
|
||||||
|
|
||||||
|
The new per-message tokens introduced here do not include the
|
||||||
|
generic GSS-API token framing used by the context establishment
|
||||||
|
tokens. These new tokens are designed to be used with newer crypto
|
||||||
|
systems that can, for example, have variable-size checksums.
|
||||||
|
|
||||||
|
4.2.1. Sequence Number
|
||||||
|
|
||||||
|
To distinguish intentionally-repeated messages from maliciously-
|
||||||
|
replayed ones, per-message tokens contain a sequence number field,
|
||||||
|
which is a 64 bit integer expressed in big endian order. After
|
||||||
|
sending a GSS_GetMIC() or GSS_Wrap() token, the sender's sequence
|
||||||
|
numbers are incremented by one.
|
||||||
|
|
||||||
|
4.2.2. Flags Field
|
||||||
|
|
||||||
|
The "Flags" field is a one-octet integer used to indicate a set of
|
||||||
|
attributes for the protected message. For example, one flag is
|
||||||
|
allocated as the direction-indicator, thus preventing an adversary
|
||||||
|
from sending back the same message in the reverse direction and
|
||||||
|
having it accepted.
|
||||||
|
|
||||||
|
The meanings of bits in this field (the least significant bit is bit
|
||||||
|
0) are as follows:
|
||||||
|
|
||||||
|
Bit Name Description
|
||||||
|
---------------------------------------------------------------
|
||||||
|
0 SentByAcceptor When set, this flag indicates the sender
|
||||||
|
is the context acceptor. When not set,
|
||||||
|
it indicates the sender is the context
|
||||||
|
initiator.
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 6
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
1 Sealed When set in Wrap tokens, this flag
|
||||||
|
indicates confidentiality is provided
|
||||||
|
for. It SHALL NOT be set in MIC tokens.
|
||||||
|
2 AcceptorSubkey A subkey asserted by the context acceptor
|
||||||
|
is used to protect the message.
|
||||||
|
|
||||||
|
The rest of available bits are reserved for future use and MUST be
|
||||||
|
cleared. The receiver MUST ignore unknown flags.
|
||||||
|
|
||||||
|
4.2.3. EC Field
|
||||||
|
|
||||||
|
The "EC" (Extra Count) field is a two-octet integer field expressed
|
||||||
|
in big endian order.
|
||||||
|
|
||||||
|
In Wrap tokens with confidentiality, the EC field is used to encode
|
||||||
|
the number of octets in the filler, as described in section 4.2.4.
|
||||||
|
|
||||||
|
In Wrap tokens without confidentiality, the EC field is used to
|
||||||
|
encode the number of octets in the trailing checksum, as described
|
||||||
|
in section 4.2.4.
|
||||||
|
|
||||||
|
4.2.4. Encryption and Checksum Operations
|
||||||
|
|
||||||
|
The encryption algorithms defined by the crypto profiles provide for
|
||||||
|
integrity protection [KCRYPTO]. Therefore no separate checksum is
|
||||||
|
needed.
|
||||||
|
|
||||||
|
The result of decryption can be longer than the original plaintext
|
||||||
|
[KCRYPTO] and the extra trailing octets are called "crypto-system
|
||||||
|
garbage". However, given the size of any plaintext data, one can
|
||||||
|
always find the next (possibly larger) size so that, when padding
|
||||||
|
the to-be-encrypted text to that size, there will be no crypto-
|
||||||
|
system garbage added [KCRYPTO].
|
||||||
|
|
||||||
|
In Wrap tokens that provide for confidentiality, the first 16 octets
|
||||||
|
of the Wrap token (the "header", as defined in section 4.2.6), are
|
||||||
|
appended to the plaintext data before encryption. Filler octets can
|
||||||
|
be inserted between the plaintext data and the "header", and the
|
||||||
|
values and size of the filler octets are chosen by implementations,
|
||||||
|
such that there is no crypto-system garbage present after the
|
||||||
|
decryption. The resulting Wrap token is {"header" |
|
||||||
|
encrypt(plaintext-data | filler | "header")}, where encrypt() is the
|
||||||
|
encryption operation (which provides for integrity protection)
|
||||||
|
defined in the crypto profile [KCRYPTO], and the RRC field in the
|
||||||
|
to-be-encrypted header contains the hex value 00 00.
|
||||||
|
|
||||||
|
In Wrap tokens that do not provide for confidentiality, the checksum
|
||||||
|
is calculated first over the to-be-signed plaintext data, and then
|
||||||
|
the first 16 octets of the Wrap token (the "header", as defined in
|
||||||
|
section 4.2.6). Both the EC field and the RRC field in the token
|
||||||
|
header are filled with zeroes for the purpose of calculating the
|
||||||
|
checksum. The resulting Wrap token is {"header" | plaintext-data |
|
||||||
|
get_mic(plaintext-data | "header")}, where get_mic() is the
|
||||||
|
|
||||||
|
Zhu Internet Draft 7
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
checksum operation for the required checksum mechanism of the chosen
|
||||||
|
encryption mechanism defined in the crypto profile [KCRYPTO].
|
||||||
|
|
||||||
|
The parameters for the key and the cipher-state in the encrypt() and
|
||||||
|
get_mic() operations have been omitted for brevity.
|
||||||
|
|
||||||
|
For MIC tokens, the checksum is first calculated over the to-be-
|
||||||
|
signed plaintext data, and then the first 16 octets of the MIC
|
||||||
|
token, where the checksum mechanism is the required checksum
|
||||||
|
mechanism of the chosen encryption mechanism defined in the crypto
|
||||||
|
profile [KCRYPTO].
|
||||||
|
|
||||||
|
The resulting Wrap and MIC tokens bind the data to the token header,
|
||||||
|
including the sequence number and the direction indicator.
|
||||||
|
|
||||||
|
4.2.5. RRC Field
|
||||||
|
|
||||||
|
The "RRC" (Right Rotation Count) field in Wrap tokens is added to
|
||||||
|
allow the data to be encrypted in-place by existing [SSPI]
|
||||||
|
applications that do not provide an additional buffer for the
|
||||||
|
trailer (the cipher text after the in-place-encrypted data) in
|
||||||
|
addition to the buffer for the header (the cipher text before the
|
||||||
|
in-place-encrypted data). The resulting Wrap token in the previous
|
||||||
|
section, excluding the first 16 octets of the token header, is
|
||||||
|
rotated to the right by "RRC" octets. The net result is that "RRC"
|
||||||
|
octets of trailing octets are moved toward the header. Consider the
|
||||||
|
following as an example of this rotation operation: Assume that the
|
||||||
|
RRC value is 3 and the token before the rotation is {"header" | aa |
|
||||||
|
bb | cc | dd | ee | ff | gg | hh}, the token after rotation would be
|
||||||
|
{"header" | ff | gg | hh | aa | bb | cc | dd | ee }, where {aa | bb
|
||||||
|
| cc |...| hh} is used to indicate the octet sequence.
|
||||||
|
|
||||||
|
The RRC field is expressed as a two-octet integer in big endian
|
||||||
|
order.
|
||||||
|
|
||||||
|
The rotation count value is chosen by the sender based on
|
||||||
|
implementation details, and the receiver MUST be able to interpret
|
||||||
|
all possible rotation count values.
|
||||||
|
|
||||||
|
4.2.6. Message Layouts
|
||||||
|
|
||||||
|
Per-message tokens start with a two-octet token identifier (TOK_ID)
|
||||||
|
field, expressed in big endian order. These tokens are defined
|
||||||
|
separately in subsequent sub-sections.
|
||||||
|
|
||||||
|
4.2.6.1. MIC Tokens
|
||||||
|
|
||||||
|
Use of the GSS_GetMIC() call yields a token, separate from the user
|
||||||
|
data being protected, which can be used to verify the integrity of
|
||||||
|
that data as received. The token has the following format:
|
||||||
|
|
||||||
|
Octet no Name Description
|
||||||
|
-----------------------------------------------------------------
|
||||||
|
0..1 TOK_ID Identification field. Tokens emitted by
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 8
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
GSS_GetMIC() contain the hex value 04 04
|
||||||
|
expressed in big endian order in this field.
|
||||||
|
2 Flags Attributes field, as described in section
|
||||||
|
4.2.2.
|
||||||
|
3..7 Filler Contains five octets of hex value FF.
|
||||||
|
8..15 SND_SEQ Sequence number field in clear text,
|
||||||
|
expressed in big endian order.
|
||||||
|
16..last SGN_CKSUM Checksum of octet 0..15 and the "to-be-
|
||||||
|
signed" data, as described in section 4.2.4.
|
||||||
|
|
||||||
|
The Filler field is included in the checksum calculation for
|
||||||
|
simplicity.
|
||||||
|
|
||||||
|
4.2.6.2. Wrap Tokens
|
||||||
|
|
||||||
|
Use of the GSS_Wrap() call yields a token, which consists of a
|
||||||
|
descriptive header, followed by a body portion that contains either
|
||||||
|
the input user data in plaintext concatenated with the checksum, or
|
||||||
|
the input user data encrypted. The GSS_Wrap() token has the
|
||||||
|
following format:
|
||||||
|
|
||||||
|
Octet no Name Description
|
||||||
|
---------------------------------------------------------------
|
||||||
|
0..1 TOK_ID Identification field. Tokens emitted by
|
||||||
|
GSS_Wrap() contain the the hex value 05 04
|
||||||
|
expressed in big endian order in this field.
|
||||||
|
2 Flags Attributes field, as described in section
|
||||||
|
4.2.2.
|
||||||
|
3 Filler Contains the hex value FF.
|
||||||
|
4..5 EC Contains the "extra count" field, in big
|
||||||
|
endian order as described in section 4.2.3.
|
||||||
|
6..7 RRC Contains the "right rotation count" in big
|
||||||
|
endian order, as described in section 4.2.5.
|
||||||
|
8..15 SND_SEQ Sequence number field in clear text,
|
||||||
|
expressed in big endian order.
|
||||||
|
16..last Data Encrypted data for Wrap tokens with
|
||||||
|
confidentiality, or plaintext data followed
|
||||||
|
by the checksum for Wrap tokens without
|
||||||
|
confidentiality, as described in section
|
||||||
|
4.2.4.
|
||||||
|
|
||||||
|
4.3. Context Deletion Tokens
|
||||||
|
|
||||||
|
Context deletion tokens are empty in this mechanism. Both peers to
|
||||||
|
a security context invoke GSS_Delete_sec_context() [RFC-2743]
|
||||||
|
independently, passing a null output_context_token buffer to
|
||||||
|
indicate that no context_token is required. Implementations of
|
||||||
|
GSS_Delete_sec_context() should delete relevant locally-stored
|
||||||
|
context information.
|
||||||
|
|
||||||
|
4.4. Token Identifier Assignment Considerations
|
||||||
|
|
||||||
|
Token identifiers (TOK_ID) from 0x60 0x00 through 0x60 0xFF
|
||||||
|
inclusive are reserved and SHALL NOT be assigned. Thus by examining
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 9
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
the first two octets of a token, one can tell unambiguously if it is
|
||||||
|
wrapped with the generic GSS-API token framing.
|
||||||
|
|
||||||
|
5. Parameter Definitions
|
||||||
|
|
||||||
|
This section defines parameter values used by the Kerberos V5 GSS-
|
||||||
|
API mechanism. It defines interface elements in support of
|
||||||
|
portability, and assumes use of C language bindings per [RFC-2744].
|
||||||
|
|
||||||
|
5.1. Minor Status Codes
|
||||||
|
|
||||||
|
This section recommends common symbolic names for minor_status
|
||||||
|
values to be returned by the Kerberos V5 GSS-API mechanism. Use of
|
||||||
|
these definitions will enable independent implementers to enhance
|
||||||
|
application portability across different implementations of the
|
||||||
|
mechanism defined in this specification. (In all cases,
|
||||||
|
implementations of GSS_Display_status() will enable callers to
|
||||||
|
convert minor_status indicators to text representations.) Each
|
||||||
|
implementation should make available, through include files or other
|
||||||
|
means, a facility to translate these symbolic names into the
|
||||||
|
concrete values which a particular GSS-API implementation uses to
|
||||||
|
represent the minor_status values specified in this section.
|
||||||
|
|
||||||
|
It is recognized that this list may grow over time, and that the
|
||||||
|
need for additional minor_status codes specific to particular
|
||||||
|
implementations may arise. It is recommended, however, that
|
||||||
|
implementations should return a minor_status value as defined on a
|
||||||
|
mechanism-wide basis within this section when that code is
|
||||||
|
accurately representative of reportable status rather than using a
|
||||||
|
separate, implementation-defined code.
|
||||||
|
|
||||||
|
5.1.1. Non-Kerberos-specific codes
|
||||||
|
|
||||||
|
GSS_KRB5_S_G_BAD_SERVICE_NAME
|
||||||
|
/* "No @ in SERVICE-NAME name string" */
|
||||||
|
GSS_KRB5_S_G_BAD_STRING_UID
|
||||||
|
/* "STRING-UID-NAME contains nondigits" */
|
||||||
|
GSS_KRB5_S_G_NOUSER
|
||||||
|
/* "UID does not resolve to username" */
|
||||||
|
GSS_KRB5_S_G_VALIDATE_FAILED
|
||||||
|
/* "Validation error" */
|
||||||
|
GSS_KRB5_S_G_BUFFER_ALLOC
|
||||||
|
/* "Couldn't allocate gss_buffer_t data" */
|
||||||
|
GSS_KRB5_S_G_BAD_MSG_CTX
|
||||||
|
/* "Message context invalid" */
|
||||||
|
GSS_KRB5_S_G_WRONG_SIZE
|
||||||
|
/* "Buffer is the wrong size" */
|
||||||
|
GSS_KRB5_S_G_BAD_USAGE
|
||||||
|
/* "Credential usage type is unknown" */
|
||||||
|
GSS_KRB5_S_G_UNKNOWN_QOP
|
||||||
|
/* "Unknown quality of protection specified" */
|
||||||
|
|
||||||
|
5.1.2. Kerberos-specific-codes
|
||||||
|
|
||||||
|
Zhu Internet Draft 10
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
GSS_KRB5_S_KG_CCACHE_NOMATCH
|
||||||
|
/* "Client principal in credentials does not match
|
||||||
|
specified name" */
|
||||||
|
GSS_KRB5_S_KG_KEYTAB_NOMATCH
|
||||||
|
/* "No key available for specified service principal" */
|
||||||
|
GSS_KRB5_S_KG_TGT_MISSING
|
||||||
|
/* "No Kerberos ticket-granting ticket available" */
|
||||||
|
GSS_KRB5_S_KG_NO_SUBKEY
|
||||||
|
/* "Authenticator has no subkey" */
|
||||||
|
GSS_KRB5_S_KG_CONTEXT_ESTABLISHED
|
||||||
|
/* "Context is already fully established" */
|
||||||
|
GSS_KRB5_S_KG_BAD_SIGN_TYPE
|
||||||
|
/* "Unknown signature type in token" */
|
||||||
|
GSS_KRB5_S_KG_BAD_LENGTH
|
||||||
|
/* "Invalid field length in token" */
|
||||||
|
GSS_KRB5_S_KG_CTX_INCOMPLETE
|
||||||
|
/* "Attempt to use incomplete security context" */
|
||||||
|
|
||||||
|
5.2. Buffer Sizes
|
||||||
|
|
||||||
|
All implementations of this specification shall be capable of
|
||||||
|
accepting buffers of at least 16K octets as input to GSS_GetMIC(),
|
||||||
|
GSS_VerifyMIC(), and GSS_Wrap(), and shall be capable of accepting
|
||||||
|
the output_token generated by GSS_Wrap() for a 16K octet input
|
||||||
|
buffer as input to GSS_Unwrap(). Support for larger buffer sizes is
|
||||||
|
optional but recommended.
|
||||||
|
|
||||||
|
6. Backwards Compatibility Considerations
|
||||||
|
|
||||||
|
The new token formats defined in this document will only be
|
||||||
|
recognized by new implementations. To address this, implementations
|
||||||
|
can always use the explicit sign or seal algorithm in [RFC-1964]
|
||||||
|
when the key type corresponds to "older" enctypes. An alternative
|
||||||
|
approach might be to retry sending the message with the sign or seal
|
||||||
|
algorithm explicitly defined as in [RFC-1964]. However this would
|
||||||
|
require either the use of a mechanism such as [RFC-2478] to securely
|
||||||
|
negotiate the method or the use out of band mechanism to choose
|
||||||
|
appropriate mechanism. For this reason, it is RECOMMENDED that the
|
||||||
|
new token formats defined in this document SHOULD be used only if
|
||||||
|
both peers are known to support the new mechanism during context
|
||||||
|
negotiation because of, for example, the use of "new" enctypes.
|
||||||
|
|
||||||
|
GSS_Unwrap() or GSS_Verify_MIC() can process a message token as
|
||||||
|
follows: it can look at the first octet of the token header, if it
|
||||||
|
is 0x60 then the token must carry the generic GSS-API pseudo ASN.1
|
||||||
|
framing, otherwise the first two octets of the token contain the
|
||||||
|
TOK_ID that uniquely identify the token message format.
|
||||||
|
|
||||||
|
7. Security Considerations
|
||||||
|
|
||||||
|
Under the current mechanism, no negotiation of algorithm types
|
||||||
|
occurs, so server-side (acceptor) implementations cannot request
|
||||||
|
that clients not use algorithm types not understood by the server.
|
||||||
|
|
||||||
|
Zhu Internet Draft 11
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
However, administration of the server's Kerberos data (e.g., the
|
||||||
|
service key) has to be done in communication with the KDC, and it is
|
||||||
|
from the KDC that the client will request credentials. The KDC
|
||||||
|
could therefore be given the task of limiting session keys for a
|
||||||
|
given service to types actually supported by the Kerberos and GSSAPI
|
||||||
|
software on the server.
|
||||||
|
|
||||||
|
This does have a drawback for cases where a service principal name
|
||||||
|
is used both for GSSAPI-based and non-GSSAPI-based communication
|
||||||
|
(most notably the "host" service key), if the GSSAPI implementation
|
||||||
|
does not understand (for example) AES [AES-KRB5] but the Kerberos
|
||||||
|
implementation does. It means that AES session keys cannot be
|
||||||
|
issued for that service principal, which keeps the protection of
|
||||||
|
non-GSSAPI services weaker than necessary. KDC administrators
|
||||||
|
desiring to limit the session key types to support interoperability
|
||||||
|
with such GSSAPI implementations should carefully weigh the
|
||||||
|
reduction in protection offered by such mechanisms against the
|
||||||
|
benefits of interoperability.
|
||||||
|
|
||||||
|
8. Acknowledgments
|
||||||
|
|
||||||
|
Ken Raeburn and Nicolas Williams corrected many of our errors in the
|
||||||
|
use of generic profiles and were instrumental in the creation of this
|
||||||
|
memo.
|
||||||
|
|
||||||
|
The text for security considerations was contributed by Ken Raeburn.
|
||||||
|
|
||||||
|
Sam Hartman and Ken Raeburn suggested the "floating trailer" idea,
|
||||||
|
namely the encoding of the RRC field.
|
||||||
|
|
||||||
|
Sam Hartman and Nicolas Williams recommended the replacing our
|
||||||
|
earlier key derivation function for directional keys with different
|
||||||
|
key usage numbers for each direction as well as retaining the
|
||||||
|
directional bit for maximum compatibility.
|
||||||
|
|
||||||
|
Paul Leach provided numerous suggestions and comments.
|
||||||
|
|
||||||
|
Scott Field, Richard Ward, Dan Simon, and Kevin Damour also provided
|
||||||
|
valuable inputs on this memo.
|
||||||
|
|
||||||
|
Jeffrey Hutzelman provided comments on channel bindings and suggested
|
||||||
|
many editorial changes.
|
||||||
|
|
||||||
|
Luke Howard provided implementations of this memo for the Heimdal
|
||||||
|
code base, and helped inter-operability testing with the Microsoft
|
||||||
|
code base, together with Love. These experiments formed the basis of
|
||||||
|
this memo.
|
||||||
|
|
||||||
|
Martin Rex provided suggestions of TOK_ID assignment recommendations
|
||||||
|
thus the token tagging in this memo is unambiguous if the token is
|
||||||
|
wrapped with the pseudo ASN.1 header.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 12
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
This document retains some of the text of RFC-1964 in relevant
|
||||||
|
sections.
|
||||||
|
|
||||||
|
9. References
|
||||||
|
|
||||||
|
9.1. Normative References
|
||||||
|
|
||||||
|
[RFC-2026] Bradner, S., "The Internet Standards Process -- Revision
|
||||||
|
3", BCP 9, RFC 2026, October 1996.
|
||||||
|
|
||||||
|
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
|
||||||
|
Requirement Levels", BCP 14, RFC 2119, March 1997.
|
||||||
|
|
||||||
|
[RFC-2743] Linn, J., "Generic Security Service Application Program
|
||||||
|
Interface Version 2, Update 1", RFC 2743, January 2000.
|
||||||
|
|
||||||
|
[RFC-2744] Wray, J., "Generic Security Service API Version 2: C-
|
||||||
|
bindings", RFC 2744, January 2000.
|
||||||
|
|
||||||
|
[RFC-1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
|
||||||
|
RFC 1964, June 1996.
|
||||||
|
|
||||||
|
[KCRYPTO] Raeburn, K., "Encryption and Checksum Specifications for
|
||||||
|
Kerberos 5", draft-ietf-krb-wg-crypto-05.txt, June, 2003. Work in
|
||||||
|
progress.
|
||||||
|
|
||||||
|
[KRBCLAR] Neuman, C., Kohl, J., Ts'o T., Yu T., Hartman, S.,
|
||||||
|
Raeburn, K., "The Kerberos Network Authentication Service (V5)",
|
||||||
|
draft-ietf-krb-wg-kerberos-clarifications-04.txt, February 2002.
|
||||||
|
Work in progress.
|
||||||
|
|
||||||
|
[AES-KRB5] Raeburn, K., "AES Encryption for Kerberos 5", draft-
|
||||||
|
raeburn-krb-rijndael-krb-05.txt, June 2003. Work in progress.
|
||||||
|
|
||||||
|
[RFC-2478] Baize, E., Pinkas D., "The Simple and Protected GSS-API
|
||||||
|
Negotiation Mechanism", RFC 2478, December 1998.
|
||||||
|
|
||||||
|
9.2. Informative References
|
||||||
|
|
||||||
|
[SSPI] Leach, P., "Security Service Provider Interface", Microsoft
|
||||||
|
Developer Network (MSDN), April 2003.
|
||||||
|
|
||||||
|
10. Author's Address
|
||||||
|
|
||||||
|
Larry Zhu
|
||||||
|
One Microsoft Way
|
||||||
|
Redmond, WA 98052 - USA
|
||||||
|
EMail: LZhu@microsoft.com
|
||||||
|
|
||||||
|
Karthik Jaganathan
|
||||||
|
One Microsoft Way
|
||||||
|
Redmond, WA 98052 - USA
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 13
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
EMail: karthikj@microsoft.com
|
||||||
|
|
||||||
|
Sam Hartman
|
||||||
|
Massachusetts Institute of Technology
|
||||||
|
77 Massachusetts Avenue
|
||||||
|
Cambridge, MA 02139 - USA
|
||||||
|
Email: hartmans@MIT.EDU
|
||||||
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|
||||||
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||||||
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||||||
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||||||
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||||||
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||||||
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||||||
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|
||||||
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|
||||||
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|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 14
|
||||||
|
Kerberos Version 5 GSS-API October 2003
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Full Copyright Statement
|
||||||
|
|
||||||
|
Copyright (C) The Internet Society (date). 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 organizations, 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 languages other than
|
||||||
|
English.
|
||||||
|
|
||||||
|
The limited permissions granted above are perpetual and will not be
|
||||||
|
revoked by the Internet Society or its successors or assigns.
|
||||||
|
|
||||||
|
This document and the information contained herein is provided on an
|
||||||
|
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
|
||||||
|
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
|
||||||
|
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
|
||||||
|
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
|
||||||
|
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
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|
||||||
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|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
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|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Internet Draft 15
|
1049
doc/standardisation/draft-ietf-krb-wg-kerberos-sam-02.txt
Normal file
1049
doc/standardisation/draft-ietf-krb-wg-kerberos-sam-02.txt
Normal file
File diff suppressed because it is too large
Load Diff
Reference in New Issue
Block a user