draft-ietf-kitten-2478bis-05.txt   rfc4178.txt 
NETWORK WORKING GROUP L. Zhu Network Working Group L. Zhu
Internet-Draft P. Leach Request for Comments: 4178 P. Leach
Obsoletes: 2478 (if approved) K. Jaganathan Obsoletes: 2478 K. Jaganathan
Expires: July 27, 2005 Microsoft Corporation Category: Standards Track Microsoft Corporation
W. Ingersoll W. Ingersoll
Sun Microsystems Sun Microsystems
January 23, 2005 October 2005
The Simple and Protected GSS-API Negotiation Mechanism
draft-ietf-kitten-2478bis-05
Status of this Memo
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http://www.ietf.org/ietf/1id-abstracts.txt. Generic Security Service Application Program Interface (GSS-API)
Negotiation Mechanism
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document specifies a negotiation mechanism for the Generic This document specifies a negotiation mechanism for the Generic
Security Service Application Program Interface (GSS-API) which is Security Service Application Program Interface (GSS-API), which is
described in RFC 2743. described in RFC 2743. GSS-API peers can use this negotiation
mechanism to choose from a common set of security mechanisms. If
GSS-API peers can use this negotiation mechanism to choose from a per-message integrity services are available on the established
common set of security mechanisms.
If per-message integrity services are available on the established
mechanism context, then the negotiation is protected against an mechanism context, then the negotiation is protected against an
attacker forcing the selection of a mechanism not desired by the attacker that forces the selection of a mechanism not desired by the
peers. peers.
This mechanism replaces RFC 2478 in order to fix defects in that This mechanism replaces RFC 2478 in order to fix defects in that
specification and to describe how to inter-operate with specification and to describe how to inter-operate with
implementations of that specification commonly deployed on the implementations of that specification that are commonly deployed on
Internet. the Internet.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
2. Conventions Used in This Document . . . . . . . . . . . . . . 5 2. Conventions Used in This Document ...............................3
3. Negotiation Protocol . . . . . . . . . . . . . . . . . . . . . 6 3. Negotiation Protocol ............................................3
3.1 Negotiation Description . . . . . . . . . . . . . . . . . 6 3.1. Negotiation Description ....................................4
3.2 Negotiation Procedure . . . . . . . . . . . . . . . . . . 7 3.2. Negotiation Procedure ......................................5
4. Token Definitions . . . . . . . . . . . . . . . . . . . . . . 10 4. Token Definitions ...............................................7
4.1 Mechanism Types . . . . . . . . . . . . . . . . . . . . . 10 4.1. Mechanism Types ............................................7
4.2 Negotiation Tokens . . . . . . . . . . . . . . . . . . . . 10 4.2. Negotiation Tokens .........................................7
4.2.1 negTokenInit . . . . . . . . . . . . . . . . . . . . . 11 4.2.1. negTokenInit ........................................8
4.2.2 negTokenResp . . . . . . . . . . . . . . . . . . . . . 12 4.2.2. negTokenResp ........................................9
5. Processing of mechListMIC . . . . . . . . . . . . . . . . . . 14 5. Processing of mechListMIC ......................................10
6. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 17 6. Extensibility ..................................................13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 7. Security Considerations ........................................13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 8. Acknowledgments ................................................14
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 9. References .....................................................14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 9.1. Normative References ......................................14
10.1 Normative References . . . . . . . . . . . . . . . . . . . 21 9.2. Informative References ....................................15
10.2 Informative References . . . . . . . . . . . . . . . . . . 21 Appendix A. SPNEGO ASN.1 Module ..................................16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 21 Appendix B. GSS-API Negotiation Support API ......................17
A. SPNEGO ASN.1 Module . . . . . . . . . . . . . . . . . . . . . 23 B.1. GSS_Set_neg_mechs Call ...................................17
B. GSS-API Negotiation Support API . . . . . . . . . . . . . . . 25 B.2. GSS_Get_neg_mechs Call ...................................18
B.1 GSS_Set_neg_mechs call . . . . . . . . . . . . . . . . . . 25 Appendix C. Changes since RFC 2478 ...............................18
B.2 GSS_Get_neg_mechs call . . . . . . . . . . . . . . . . . . 25 Appendix D. mechListMIC Computation Example ......................20
C. Changes since RFC2478 . . . . . . . . . . . . . . . . . . . . 27
D. mechListMIC Computation Example . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . 30
1. Introduction 1. Introduction
The GSS-API [RFC2743] provides a generic interface which can be The GSS-API [RFC2743] provides a generic interface that can be
layered atop different security mechanisms such that if communicating layered atop different security mechanisms such that, if
peers acquire GSS-API credentials for the same security mechanism, communicating peers acquire GSS-API credentials for the same security
then a security context may be established between them (subject to mechanism, then a security context may be established between them
policy). However, GSS-API does not prescribe the method by which (subject to policy). However, GSS-API does not prescribe the method
GSS-API peers can establish whether they have a common security by which GSS-API peers can establish whether they have a common
mechanism. security mechanism.
The Simple and Protected GSS-API Negotiation (SPNEGO) mechanism The Simple and Protected GSS-API Negotiation (SPNEGO) mechanism
defined here is a pseudo security mechanism, which enables GSS-API defined here is a pseudo security mechanism that enables GSS-API
peers to determine in-band whether their credentials support a common peers to determine in-band whether their credentials support a common
set of one or more GSS-API security mechanisms, and if so, to invoke set of one or more GSS-API security mechanisms; if so, it invokes the
the normal security context establishment for a selected common normal security context establishment for a selected common security
security mechanism. This is most useful for applications which mechanism. This is most useful for applications that depend on GSS-
depend on GSS-API implementations and share multiple mechanisms API implementations and share multiple mechanisms between the peers.
between the peers.
The SPNEGO mechanism negotiation is based on the following model: the The SPNEGO mechanism negotiation is based on the following model: the
initiator proposes a list of security mechanism(s), in decreasing initiator proposes a list of security mechanism(s), in decreasing
preference order (favorite choice first), the acceptor (also known as preference order (favorite choice first), the acceptor (also known as
the target) either accepts the initiator's preferred security the target) either accepts the initiator's preferred security
mechanism (the first in the list), or chooses one that is available mechanism (the first in the list) or chooses one of the available
from the offered list, or rejects the proposed value(s). The target mechanisms from the offered list; if neither is acceptable, the
then informs the initiator of its choice. acceptor rejects the proposed value(s). The target then informs the
initiator of its choice.
Once a common security mechanism is chosen, mechanism-specific Once a common security mechanism is chosen, mechanism-specific
options MAY be negotiated as part of the selected mechanism's context options MAY be negotiated as part of the selected mechanism's context
establishment. These negotiations (if any) are internal to the establishment. These negotiations (if any) are internal to the
mechanism and opaque to the SPNEGO protocol. As such they are mechanism and opaque to the SPNEGO protocol. As such, they are
outside the scope of this document. outside the scope of this document.
If per-message integrity services are available on the established If per-message integrity services [RFC2743] are available on the
mechanism security context, then the negotiation is protected to established mechanism security context, then the negotiation is
ensure that the mechanism list has not been modified. In cases where protected to ensure that the mechanism list has not been modified.
an attacker could have materially influenced the negotiation, peers In cases where an attacker could have materially influenced the
exchange message integrity code (MIC) tokens to confirm the mechanism negotiation, peers exchange message integrity code (MIC) tokens to
list has not been modified. If no action of an attacker could have confirm that the mechanism list has not been modified. If no action
materially modified the outcome of the negotiation, the exchange of of an attacker could have materially modified the outcome of the
MIC tokens is optional (see Section 5). Allowing MIC tokens to be negotiation, the exchange of MIC tokens is optional (see Section 5).
optional in this case provides interoperability with existing Allowing MIC tokens to be optional in this case provides
implementations while still protecting the negotiation. This interoperability with existing implementations while still protecting
interoperability comes at the cost of increased complexity. the negotiation. This interoperability comes at the cost of
increased complexity.
SPNEGO relies on the concepts developed in the GSS-API specification SPNEGO relies on the concepts developed in the GSS-API specification
[RFC2743]. The negotiation data is encapsulated in context-level [RFC2743]. The negotiation data is encapsulated in context-level
tokens. Therefore, callers of the GSS-API do not need to be aware of tokens. Therefore, callers of the GSS-API do not need to be aware of
the existence of the negotiation tokens but only of the new the existence of the negotiation tokens, but only of the new pseudo-
pseudo-security mechanism. A failure in the negotiation phase causes security mechanism. A failure in the negotiation phase causes a
a major status code to be returned: GSS_S_BAD_MECH. major status code to be returned: GSS_S_BAD_MECH.
2. Conventions Used in This Document 2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Negotiation Protocol 3. Negotiation Protocol
When the established mechanism context provides integrity protection, When the established mechanism context provides integrity protection,
the mechanism negotiation can be protected. When acquiring the mechanism negotiation can be protected. When acquiring
negotiated security mechanism tokens, per-message integrity services negotiated security mechanism tokens, per-message integrity services
are always requested by the SPNEGO mechanism. are always requested by the SPNEGO mechanism.
When the established mechanism context supports per-message integrity When the established mechanism context supports per-message integrity
services, SPNEGO guarantees that the selected mechanism is mutually services, SPNEGO guarantees that the selected mechanism is mutually
preferred. preferred.
This section describes the negotiation process of this protocol. This section describes the negotiation process of this protocol.
3.1 Negotiation Description 3.1. Negotiation Description
The first negotiation token sent by the initiator contains an ordered The first negotiation token sent by the initiator contains an ordered
list of mechanisms in decreasing preference order (favorite mechanism list of mechanisms in decreasing preference order (favorite mechanism
first), and optionally the initial mechanism token for the preferred first), and optionally the initial mechanism token for the preferred
mechanism of the initiator (i.e., the first in the list). (Note that mechanism of the initiator (i.e., the first in the list). (Note that
the list MUST NOT contain either this SPNEGO mechanism itself or any the list MUST NOT contain this SPNEGO mechanism itself or any
mechanism for which the client does not have appropriate mechanism for which the client does not have appropriate
credentials.) credentials.)
The target then processes the token from the initiator. This will The target then processes the token from the initiator. This will
result in one of four possible states (as defined in Section 4.2.2) result in one of four possible states (as defined in Section 4.2.2)
being returned in the reply message: accept-completed, being returned in the reply message: accept-completed, accept-
accept-incomplete, reject, or request-mic. A reject state will incomplete, reject, or request-mic. A reject state will terminate
terminate the negotiation; an accept-completed state indicates that the negotiation; an accept-completed state indicates that the
not only was the initiator-selected mechanism acceptable to the initiator-selected mechanism was acceptable to the target, and that
target, but also that the security mechanism token embedded in the the security mechanism token embedded in the first negotiation
first negotiation message was sufficient to complete the message was sufficient to complete the authentication; an accept-
authentication; an accept-incomplete state indicates that further incomplete state indicates that further message exchange is needed
message exchange is needed but the MIC token exchange as described in but the MIC token exchange (as described in Section 5) is OPTIONAL; a
Section 5 is OPTIONAL; a request-mic state (this state can only be request-mic state (this state can only be present in the first reply
present in the first reply message from the target) indicates the MIC message from the target) indicates that the MIC token exchange is
token exchange is REQUIRED if per-message integrity services are REQUIRED if per-message integrity services are available.
available.
Unless the preference order is specified by the application, the Unless the preference order is specified by the application, the
policy by which the target chooses a mechanism is an policy by which the target chooses a mechanism is an implementation-
implementation-specific local matter. In the absence of an specific, local matter. In the absence of an application-specified
application specified preference order or other policy, the target preference order or other policy, the target SHALL choose the first
SHALL choose the first mechanism in the initiator proposed list for mechanism in the initiator proposed list for which it has valid
which it has valid credentials. credentials.
In case of a successful negotiation, the security mechanism in the In case of a successful negotiation, the security mechanism in the
first reply message represents the value suitable for the target, first reply message represents the value suitable for the target that
chosen from the list offered by the initiator. was chosen from the list offered by the initiator.
In case of an unsuccessful negotiation, the reject state is returned In case of an unsuccessful negotiation, the reject state is returned,
and generating a context level negotiation token is OPTIONAL. and the generation of a context-level negotiation token is OPTIONAL.
Once a mechanism has been selected, context establishment tokens Once a mechanism has been selected, context establishment tokens
specific to the selected mechanism are carried within the negotiation specific to the selected mechanism are carried within the negotiation
tokens. tokens.
Lastly, MIC tokens may be exchanged to ensure the authenticity of the Lastly, MIC tokens may be exchanged to ensure the authenticity of the
mechanism list received by the target. mechanism list received by the target.
To avoid conflicts with the use of MIC tokens by SPNEGO, To avoid conflicts with the use of MIC tokens by SPNEGO, partially-
partially-established contexts MUST NOT be used for per-message established contexts MUST NOT be used for per-message calls. To
calls. To guarantee this, the prot_ready_state [RFC2743] MUST be set guarantee this, the prot_ready_state [RFC2743] MUST be set to false
to false on return from GSS_Init_sec_context() and on return from GSS_Init_sec_context() and GSS_Accept_sec_context(),
GSS_Accept_sec_context() even if the underlying mechanism returned even if the underlying mechanism returned true.
true.
Note that in order to avoid an extra round trip, the first context Note that in order to avoid an extra round trip, the first context
establishment token of the initiator's preferred mechanism SHOULD be establishment token of the initiator's preferred mechanism SHOULD be
embedded in the initial negotiation message (as defined in embedded in the initial negotiation message (as defined in Section
Section 4.2). (This mechanism token is referred to as the optimistic 4.2). (This mechanism token is referred to as the optimistic
mechanism token in this document.) In addition, using the optimistic mechanism token in this document.) In addition, using the optimistic
mechanism token allows the initiator to recover from non-fatal errors mechanism token allows the initiator to recover from non-fatal errors
encountered trying to produce the first mechanism token before a encountered when trying to produce the first mechanism token before a
mechanism can be selected. Implementations MAY omit the optimistic mechanism can be selected. In cases where the initiator's preferred
mechanism token in cases where the likelihood of the initiator's mechanism is not likely to be selected by the acceptor because of the
preferred mechanism not being selected by the acceptor is significant significant cost of its generation, implementations MAY omit the
given the cost of generating it. optimistic mechanism token.
3.2 Negotiation Procedure 3.2. Negotiation Procedure
The basic form of the procedure assumes that per-message integrity The basic form of the procedure assumes that per-message integrity
services are available on the established mechanism context, and it services are available on the established mechanism context, and it
is summarized as follows: is summarized as follows:
(a) The GSS-API initiator invokes GSS_Init_sec_context() as normal, a) The GSS-API initiator invokes GSS_Init_sec_context() as normal,
but requests that SPNEGO be used. SPNEGO can either be explicitly but requests that SPNEGO be used. SPNEGO can either be explicitly
requested or accepted as the default mechanism. requested or accepted as the default mechanism.
(b) The initiator GSS-API implementation generates a negotiation b) The initiator GSS-API implementation generates a negotiation token
token containing a list of one or more security mechanisms that containing a list of one or more security mechanisms that are
are available based on the credentials used for this context available based on the credentials used for this context
establishment, and optionally the initial mechanism token for the establishment, and optionally on the initial mechanism token for
first mechanism in the list. the first mechanism in the list.
(c) The GSS-API initiator application sends the token to the target c) The GSS-API initiator application sends the token to the target
application. The GSS-API target application passes the token by application. The GSS-API target application passes the token by
invoking GSS_Accept_sec_context(). The acceptor will do one of invoking GSS_Accept_sec_context(). The acceptor will do one of
the following: the following:
(I) If none of the proposed mechanisms are acceptable, the I) If none of the proposed mechanisms are acceptable, the
negotiation SHALL be terminated. GSS_Accept_sec_context negotiation SHALL be terminated. GSS_Accept_sec_context
indicates GSS_S_BAD_MECH. The acceptor MAY output a indicates GSS_S_BAD_MECH. The acceptor MAY output a
negotiation token containing a reject state. negotiation token containing a reject state.
(II) If either the initiator's preferred mechanism is not II) If either the initiator's preferred mechanism is not accepted
accepted by the target or this mechanism is accepted but it by the target or this mechanism is accepted but is not the
is not the acceptor's most preferred mechanism (i.e., the acceptor's most preferred mechanism (i.e., the MIC token
MIC token exchange as described in Section 5 is required), exchange as described in Section 5 is required),
GSS_Accept_sec_context() indicates GSS_S_CONTINUE_NEEDED. GSS_Accept_sec_context() indicates GSS_S_CONTINUE_NEEDED.
The acceptor MUST output a negotiation token containing a The acceptor MUST output a negotiation token containing a
request-mic state. request-mic state.
(III) Otherwise if at least one additional negotiation token III) Otherwise, if at least one additional negotiation token from
from the initiator is needed to establish this context, the initiator is needed to establish this context,
GSS_Accept_sec_context() indicates GSS_S_CONTINUE_NEEDED and GSS_Accept_sec_context() indicates GSS_S_CONTINUE_NEEDED and
outputs a negotiation token containing an accept-incomplete outputs a negotiation token containing an accept-incomplete
state. state.
(IV) Otherwise no additional negotiation token from the IV) Otherwise, no additional negotiation token from the initiator
initiator is needed to establish this context, is needed to establish this context, GSS_Accept_sec_context()
GSS_Accept_sec_context() indicates GSS_S_COMPLETE and indicates GSS_S_COMPLETE and outputs a negotiation token
outputs a negotiation token containing an accept_complete containing an accept_complete state.
state.
If the initiator's preferred mechanism is accepted, and an If the initiator's preferred mechanism is accepted, and an
optimistic mechanism token was included, this mechanism token MUST optimistic mechanism token was included, this mechanism token MUST
be passed to the selected mechanism by invoking be passed to the selected mechanism by invoking
GSS_Accept_sec_context() and if a response mechanism token is GSS_Accept_sec_context(). If a response mechanism token is
returned, it MUST be included in the response negotiation token. returned, it MUST be included in the response negotiation token.
Otherwise, the target will not generate a response mechanism token Otherwise, the target will not generate a response mechanism token
in the first reply. in the first reply.
(d) The GSS-API target application returns the negotiation token to d) The GSS-API target application returns the negotiation token to
the initiator application. The GSS-API initiator application the initiator application. The GSS-API initiator application
passes the token by invoking GSS_Init_sec_context(). The security passes the token by invoking GSS_Init_sec_context(). The security
context initialization is then continued according to the standard context initialization is then continued according to the standard
GSS-API conventions for the selected mechanism, where the tokens GSS-API conventions for the selected mechanism, where the tokens
of the selected mechanism are encapsulated in negotiation messages of the selected mechanism are encapsulated in negotiation messages
(see Section 4) until GSS_S_COMPLETE is returned for both the (see Section 4) until GSS_S_COMPLETE is returned for both the
initiator and the target by the selected security mechanism. initiator and the target by the selected security mechanism.
(e) MIC tokens are then either skipped or exchanged according to e) MIC tokens are then either skipped or exchanged according to
Section 5. Section 5.
Note that the *_req_flag input parameters for context establishment Note that the *_req_flag input parameters for context establishment
are relative to the selected mechanism, as are the *_state output are relative to the selected mechanism, as are the *_state output
parameters. i.e., these parameters are not applicable to the parameters. That is, these parameters are not applicable to the
negotiation process per se. negotiation process per se.
On receipt of a negotiation token on the target side, a GSS-API On receipt of a negotiation token on the target side, a GSS-API
implementation that does not support negotiation would indicate the implementation that does not support negotiation would indicate the
GSS_S_BAD_MECH status as if a particular basic security mechanism had GSS_S_BAD_MECH status as though a particular basic security mechanism
been requested and was not supported. had been requested and was not supported.
When a GSS-API credential is acquired for the SPNEGO mechanism the When a GSS-API credential is acquired for the SPNEGO mechanism, the
implementation SHOULD produce a credential element for the SPNEGO implementation SHOULD produce a credential element for the SPNEGO
mechanism which internally contains GSS-API credential elements for mechanism that internally contains GSS-API credential elements for
all mechanisms for which the principal has credentials available, all mechanisms for which the principal has credentials available,
except for any mechanisms which are not to be negotiated, either as except for any mechanisms that are not to be negotiated, per
per implementation-, site- or application-specific policy. See implementation-, site-, or application-specific policy. See Appendix
Appendix B for interfaces for expressing application policy. B for interfaces for expressing application policy.
4. Token Definitions 4. Token Definitions
The type definitions in this section assume an ASN.1 module The type definitions in this section assume an ASN.1 module
definition of the following form: definition of the following form:
SPNEGOASNOneSpec { SPNEGOASNOneSpec {
iso(1) identified-organization(3) dod(6) internet(1) iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanism(5) snego (2) modules(4) spec2(2) security(5) mechanism(5) snego (2) modules(4) spec2(2)
} DEFINITIONS EXPLICIT TAGS ::= BEGIN } DEFINITIONS EXPLICIT TAGS ::= BEGIN
-- rest of definitions here -- rest of definitions here
END END
This specifies that the tagging context for the module will be This specifies that the tagging context for the module will be
explicit and non-automatic. explicit and non-automatic.
The encoding of SPNEGO protocol messages shall obey the Distinguished The encoding of the SPNEGO protocol messages shall obey the
Encoding Rules (DER) of ASN.1 as described in [X690]. Distinguished Encoding Rules (DER) of ASN.1, as described in [X690].
4.1 Mechanism Types 4.1. Mechanism Types
In this negotiation model, each OID represents one GSS-API mechanism In this negotiation model, each OID represents one GSS-API mechanism
or one variant (see Section 6) of it according to [RFC2743]. or one variant (see Section 6) of it, according to [RFC2743].
MechType ::= OBJECT IDENTIFIER MechType ::= OBJECT IDENTIFIER
-- OID represents each security mechanism as suggested by -- OID represents each security mechanism as suggested by
-- [RFC2743] -- [RFC2743]
MechTypeList ::= SEQUENCE OF MechType MechTypeList ::= SEQUENCE OF MechType
4.2 Negotiation Tokens 4.2. Negotiation Tokens
The syntax of the initial negotiation tokens follows the The syntax of the initial negotiation tokens follows the
initialContextToken syntax defined in Section 3.1 of [RFC2743]. The initialContextToken syntax defined in Section 3.1 of [RFC2743]. The
SPNEGO pseudo mechanism is identified by the Object Identifier SPNEGO pseudo mechanism is identified by the Object Identifier
iso.org.dod.internet.security.mechanism.snego (1.3.6.1.5.5.2). iso.org.dod.internet.security.mechanism.snego (1.3.6.1.5.5.2).
Subsequent tokens MUST NOT be encapsulated in this GSS-API generic Subsequent tokens MUST NOT be encapsulated in this GSS-API generic
token framing. token framing.
This section specifies the syntax of the inner token for the initial This section specifies the syntax of the inner token for the initial
message and the syntax of subsequent context establishment tokens. message and the syntax of subsequent context establishment tokens.
NegotiationToken ::= CHOICE { NegotiationToken ::= CHOICE {
negTokenInit [0] NegTokenInit, negTokenInit [0] NegTokenInit,
negTokenResp [1] NegTokenResp negTokenResp [1] NegTokenResp
} }
4.2.1 negTokenInit 4.2.1. negTokenInit
NegTokenInit ::= SEQUENCE { NegTokenInit ::= SEQUENCE {
mechTypes [0] MechTypeList, mechTypes [0] MechTypeList,
reqFlags [1] ContextFlags OPTIONAL, reqFlags [1] ContextFlags OPTIONAL,
-- inherited from RFC 2478 for backward compatibility, -- inherited from RFC 2478 for backward compatibility,
-- RECOMMENDED to be left out -- RECOMMENDED to be left out
mechToken [2] OCTET STRING OPTIONAL, mechToken [2] OCTET STRING OPTIONAL,
mechListMIC [3] OCTET STRING OPTIONAL, mechListMIC [3] OCTET STRING OPTIONAL,
... ...
} }
skipping to change at page 11, line 36 skipping to change at page 8, line 36
anonFlag (4), anonFlag (4),
confFlag (5), confFlag (5),
integFlag (6) integFlag (6)
} (SIZE (32)) } (SIZE (32))
This is the syntax for the inner token of the initial negotiation This is the syntax for the inner token of the initial negotiation
message. message.
mechTypes mechTypes
This field contains one or more security mechanisms available This field contains one or more security mechanisms available for
for the initiator in decreasing preference order (favorite the initiator, in decreasing preference order (favorite choice
choice first). first).
reqFlags reqFlags
This field, if present, contains the service options that are This field, if present, contains the service options that are
requested to establish the context (the req_flags parameter of requested to establish the context (the req_flags parameter of
GSS_Init_sec_context()). This field is inherited from RFC 2478 GSS_Init_sec_context()). This field is inherited from RFC 2478
and it is not integrity protected. For implementations of this and is not integrity protected. For implementations of this
specification the initiator SHOULD omit this reqFlags field, specification, the initiator SHOULD omit this reqFlags field and
and the acceptor MUST ignore this reqFlags field. the acceptor MUST ignore this reqFlags field.
The size constraint on the ContextFlags ASN.1 type only applies to
the abstract type. The ASN.1 DER requires that all trailing zero
bits be truncated from the encoding of a bit string type whose
abstract definition includes named bits. Implementations should
not expect to receive exactly 32 bits in an encoding of
ContextFlags.
mechToken mechToken
This field, if present, contains the optimistic mechanism This field, if present, contains the optimistic mechanism token.
token.
mechlistMIC mechlistMIC
This field, if present, contains a MIC token for the mechanism This field, if present, contains an MIC token for the mechanism
list in the initial negotiation message. This MIC token is list in the initial negotiation message. This MIC token is
computed according to Section 5. computed according to Section 5.
4.2.2 negTokenResp 4.2.2. negTokenResp
NegTokenResp ::= SEQUENCE { NegTokenResp ::= SEQUENCE {
negState [0] ENUMERATED { negState [0] ENUMERATED {
accept-completed (0), accept-completed (0),
accept-incomplete (1), accept-incomplete (1),
reject (2), reject (2),
request-mic (3) request-mic (3)
} OPTIONAL, } OPTIONAL,
-- REQUIRED in the first reply from the target -- REQUIRED in the first reply from the target
supportedMech [1] MechType OPTIONAL, supportedMech [1] MechType OPTIONAL,
skipping to change at page 12, line 42 skipping to change at page 9, line 43
This is the syntax for all subsequent negotiation messages. This is the syntax for all subsequent negotiation messages.
negState negState
This field, if present, contains the state of the negotiation. This field, if present, contains the state of the negotiation.
This can be: This can be:
accept-completed accept-completed
No further negotiation message from the peer is expected, No further negotiation message from the peer is expected, and
and the security context is established for the sender. the security context is established for the sender.
accept-incomplete accept-incomplete
At least one more negotiation message from the peer is At least one additional negotiation message from the peer is
needed to establish the security context. needed to establish the security context.
reject reject
The sender terminates the negotiation. The sender terminates the negotiation.
request-mic request-mic
The sender indicates that the exchange of MIC tokens, as The sender indicates that the exchange of MIC tokens, as
described in Section 5, will be REQUIRED if per-message described in Section 5, will be REQUIRED if per-message
integrity services are available on the mechanism context to integrity services are available on the mechanism context to be
be established. This value SHALL only be present in the established. This value SHALL only be present in the first
first reply from the target. reply from the target.
This field is REQUIRED in the first reply from the target, and This field is REQUIRED in the first reply from the target, and is
it is OPTIONAL thereafter. When negState is absent the actual OPTIONAL thereafter. When negState is absent, the actual state
state should be inferred from the state of the negotiated should be inferred from the state of the negotiated mechanism
mechanism context. context.
supportedMech supportedMech
This field SHALL only be present in the first reply from the This field SHALL only be present in the first reply from the
target. It MUST be one of the mechanism(s) offered by the target. It MUST be one of the mechanism(s) offered by the
initiator. initiator.
ResponseToken ResponseToken
This field, if present, contains tokens specific to the This field, if present, contains tokens specific to the mechanism
mechanism selected. selected.
mechlistMIC mechlistMIC
This field, if present, contains a MIC token for the mechanism This field, if present, contains an MIC token for the mechanism
list in the initial negotiation message. This MIC token is list in the initial negotiation message. This MIC token is
computed according to Section 5. computed according to Section 5.
5. Processing of mechListMIC 5. Processing of mechListMIC
If the mechanism selected by the negotiation does not support If the mechanism selected by the negotiation does not support
integrity protection, then no mechlistMIC token is used. integrity protection, then no mechlistMIC token is used.
Otherwise, if the accepted mechanism is the most preferred mechanism Otherwise, if the accepted mechanism is the most preferred mechanism
of both the initiator and the acceptor, then the MIC token exchange, of both the initiator and the acceptor, then the MIC token exchange,
as described later in this section, is OPTIONAL. A mechanism is the as described later in this section, is OPTIONAL. A mechanism is the
acceptor's most preferred mechanism if there is no other mechanism acceptor's most preferred mechanism if there is no other mechanism
which, had it been present in the mechanism list, the acceptor would that the acceptor would have preferred over the accepted mechanism
have preferred over the accepted mechanism. had it been present in the mechanism list.
In all other cases, MIC tokens MUST be exchanged after the mechanism In all other cases, MIC tokens MUST be exchanged after the mechanism
context is fully established. context is fully established.
a) The mechlistMIC token (or simply the MIC token) is computed over a) The mechlistMIC token (or simply the MIC token) is computed over
the mechanism list in the initial negotiation message by invoking the mechanism list in the initial negotiation message by invoking
GSS_GetMIC() as follows: the input context_handle is the GSS_GetMIC() as follows: the input context_handle is the
established mechanism context, the input qop_req is 0, and the established mechanism context, the input qop_req is 0, and the
input message is the DER encoding of the value of type input message is the DER encoding of the value of type
MechTypeList which is contained in the "mechTypes" field of the MechTypeList, which is contained in the "mechTypes" field of the
NegTokenInit. The input message is NOT the DER encoding of the NegTokenInit. The input message is NOT the DER encoding of the
type "[0] MechTypeList". type "[0] MechTypeList".
b) If the selected mechanism exchanges an even number of mechanism b) If the selected mechanism exchanges an even number of mechanism
tokens (i.e., the acceptor sends the last mechanism token), the tokens (i.e., the acceptor sends the last mechanism token), the
acceptor does the following when generating the negotiation acceptor does the following when generating the negotiation
message containing the last mechanism token: if the MIC token message containing the last mechanism token: if the MIC token
exchange is optional, GSS_Accept_sec_context() either indicates exchange is optional, GSS_Accept_sec_context() either indicates
GSS_S_COMPLETE and does not include a mechlistMIC token, or GSS_S_COMPLETE and does not include a mechlistMIC token, or
indicates GSS_S_CONTINUE_NEEDED and includes a mechlistMIC token indicates GSS_S_CONTINUE_NEEDED and includes a mechlistMIC token
and an accept-incomplete state; if the MIC token exchange is and an accept-incomplete state; if the MIC token exchange is
required, GSS_Accept_sec_context() indicates required, GSS_Accept_sec_context() indicates GSS_S_CONTINUE_NEEDED
GSS_S_CONTINUE_NEEDED, and includes a mechlistMIC token. and includes a mechlistMIC token. Acceptors that wish to be
Acceptors that wish to be compatible with legacy Windows SPNEGO compatible with legacy Windows SPNEGO implementations, as
implementations as described in Appendix C should not generate a described in Appendix C, should not generate a mechlistMIC token
mechlistMIC token when the MIC token exchange is not required. when the MIC token exchange is not required. The initiator then
The initiator then processes the last mechanism token, and does processes the last mechanism token, and does one of the following:
one of the following:
(I) If a mechlistMIC token was included, and is correctly I) If a mechlistMIC token was included and is correctly
verified, GSS_Init_sec_context() indicates GSS_S_COMPLETE. The verified, GSS_Init_sec_context() indicates GSS_S_COMPLETE.
output negotiation message contains a mechlistMIC token, and an The output negotiation message contains a mechlistMIC token
accept_complete state. The acceptor MUST then verify this and an accept_complete state. The acceptor MUST then verify
mechlistMIC token. this mechlistMIC token.
(II) If a mechlistMIC token was included but is incorrect, the II) If a mechlistMIC token was included but is incorrect, the
negotiation SHALL be terminated. GSS_Init_sec_context() negotiation SHALL be terminated. GSS_Init_sec_context()
indicates GSS_S_DEFECTIVE_TOKEN. indicates GSS_S_DEFECTIVE_TOKEN.
(III) If no mechlistMIC token was included, and the MIC token III) If no mechlistMIC token was included and the MIC token
exchange is not required, GSS_Init_sec_context() indicates exchange is not required, GSS_Init_sec_context() indicates
GSS_S_COMPLETE with no output token. GSS_S_COMPLETE with no output token.
(IV) If no mechlistMIC token was included, but the MIC token IV) If no mechlistMIC token was included but the MIC token
exchange is required, the negotiation SHALL be terminated. exchange is required, the negotiation SHALL be terminated.
GSS_Accept_sec_context() indicates GSS_S_DEFECTIVE_TOKEN. GSS_Accept_sec_context() indicates GSS_S_DEFECTIVE_TOKEN.
c) In the case that the chosen mechanism exchanges an odd number of c) In the case that the chosen mechanism exchanges an odd number of
mechanism tokens (i.e., the initiator sends the last mechanism mechanism tokens (i.e., the initiator sends the last mechanism
token), the initiator does the following when generating the token), the initiator does the following when generating the
negotiation message containing the last mechanism token: if the negotiation message containing the last mechanism token: if the
negState was request-mic in the first reply from the target, a negState was request-mic in the first reply from the target, a
mechlistMIC token MUST be included, otherwise the mechlistMIC mechlistMIC token MUST be included; otherwise, the mechlistMIC
token is OPTIONAL. (Note that the MIC token exchange is required token is OPTIONAL. (Note that the MIC token exchange is required
if a mechanism other than the initiator's first choice is chosen.) if a mechanism other than the initiator's first choice is chosen.)
In the case that the optimistic mechanism token is the only In the case that the optimistic mechanism token is the only
mechanism token for the initiator's preferred mechanism, the mechanism token for the initiator's preferred mechanism, the
mechlistMIC token is OPTIONAL. Whether or not the mechlistMIC mechlistMIC token is OPTIONAL. Whether the mechlistMIC token is
token is included, GSS_Init_sec_context() indicates included, GSS_Init_sec_context() indicates GSS_S_CONTINUE_NEEDED.
GSS_S_CONTINUE_NEEDED. Initiators that wish to be compatible with Initiators that wish to be compatible with legacy Windows SPNEGO
legacy Windows SPNEGO implementations as described in Appendix C implementations, as described in Appendix C, should not generate a
should not generate a mechlistMIC token when the MIC token mechlistMIC token when the MIC token exchange is not required.
exchange is not required. The acceptor then processes the last The acceptor then processes the last mechanism token and does one
mechanism token and does one of the following: of the following:
(I) If a mechlistMIC token was included and is correctly verified, I) If a mechlistMIC token was included and is correctly
GSS_Accept_sec_context() indicates GSS_S_COMPLETE. The output verified, GSS_Accept_sec_context() indicates GSS_S_COMPLETE.
negotiation message contains a mechlistMIC token and an The output negotiation message contains a mechlistMIC token
accept_complete state. The initiator MUST then verify this and an accept_complete state. The initiator MUST then verify
mechlistMIC token. this mechlistMIC token.
(II) If a mechlistMIC token was included but is incorrect, the II) If a mechlistMIC token was included but is incorrect, the
negotiation SHALL be terminated. GSS_Accept_sec_context() negotiation SHALL be terminated. GSS_Accept_sec_context()
indicates GSS_S_DEFECTIVE_TOKEN. indicates GSS_S_DEFECTIVE_TOKEN.
(III) If no mechlistMIC token was included and the mechlistMIC III) If no mechlistMIC token was included and the mechlistMIC
token exchange is not required, GSS_Accept_sec_context() token exchange is not required, GSS_Accept_sec_context()
indicates GSS_S_COMPLETE. The output negotiation message indicates GSS_S_COMPLETE. The output negotiation message
contains an accept_complete state. contains an accept_complete state.
(IV) In the case that the optimistic mechanism token is also the IV) In the case that the optimistic mechanism token is also the
last mechanism token (when the initiator's preferred mechanism last mechanism token (when the initiator's preferred
is accepted by the target) and the target sends a request-mic mechanism is accepted by the target) and the target sends a
state but the initiator did not send a mechlistMIC token, the request-mic state but the initiator did not send a
target then MUST include a mechlistMIC token in that first mechlistMIC token, the target then MUST include a mechlistMIC
reply. GSS_Accept_sec_context() indicates token in that first reply. GSS_Accept_sec_context()
GSS_S_CONTINUE_NEEDED. The initiator MUST verify the received indicates GSS_S_CONTINUE_NEEDED. The initiator MUST verify
mechlistMIC token and generate a mechlistMIC token to send back the received mechlistMIC token and generate a mechlistMIC
to the target. The target SHALL in turn verify the returned token to send back to the target. The target SHALL, in turn,
mechlistMIC token and complete the negotiation. verify the returned mechlistMIC token and complete the
negotiation.
(V) If no mechlistMIC token was included and the acceptor sent a V) If no mechlistMIC token was included and the acceptor sent a
request-mic state in the first reply message (the exchange of request-mic state in the first reply message (the exchange of
MIC tokens is required), the negotiation SHALL be terminated. MIC tokens is required), the negotiation SHALL be terminated.
GSS_Accept_sec_context() indicates GSS_S_DEFECTIVE_TOKEN. GSS_Accept_sec_context() indicates GSS_S_DEFECTIVE_TOKEN.
6. Extensibility 6. Extensibility
Two mechanisms are provided for extensibility. First, the ASN.1 Two mechanisms are provided for extensibility. First, the ASN.1
structures in this specification MAY be expanded by IETF standards structures in this specification MAY be expanded by IETF standards
action. Implementations receiving unknown fields MUST ignore these action. Implementations receiving unknown fields MUST ignore these
fields. fields.
Secondly, OIDs corresponding to a desired mechanism attribute (i.e., Secondly, OIDs corresponding to a desired mechanism attribute (i.e.,
mechanism variants) may be included in the set of preferred mechanism variants) may be included in the set of preferred
mechanisms by an initiator. The acceptor can choose to honor this mechanisms by an initiator. The acceptor can choose to honor this
request by preferring mechanisms that have the included attributes. request by preferring mechanisms that have the included attributes.
Future work within the Kitten working group is expected to Future work within the Kitten working group is expected to
standardize common attributes that SPNEGO mechanisms may wish to standardize common attributes that SPNEGO mechanisms may wish to
support. At this time it is sufficient to say that initiators MAY support. At this time, it is sufficient to say that initiators MAY
include OIDs that do not correspond to mechanisms. Such OIDs MAY include OIDs that do not correspond to mechanisms. Such OIDs MAY
influence the acceptor's choice of mechanism. As discussed in influence the acceptor's choice of mechanism. As discussed in
Section 5, if there are mechanisms that if present in the initiator's Section 5, if there are mechanisms that, if present in the
list of mechanisms might be preferred by the acceptor to the initiator's list of mechanisms, might be preferred by the acceptor
initiator's preferred mechanism, the acceptor MUST demand the MIC instead of the initiator's preferred mechanism, the acceptor MUST
token exchange. As the consequence, acceptors MUST demand the MIC demand the MIC token exchange. As the consequence, acceptors MUST
token exchange if they support negotiation of attributes not demand the MIC token exchange if they support negotiation of
available in the initiator's preferred mechanism regardless of attributes not available in the initiator's preferred mechanism,
whether the initiator actually requested these attributes. regardless of whether the initiator actually requested these
attributes.
7. Security Considerations 7. Security Considerations
In order to produce the MIC token for the mechanism list, the In order to produce the MIC token for the mechanism list, the
mechanism must provide integrity protection. When the selected mechanism must provide integrity protection. When the selected
mechanism does not support integrity protection, the negotiation is mechanism does not support integrity protection, the negotiation is
vulnerable: an active attacker can force it to use a security vulnerable: an active attacker can force it to use a security
mechanism that is not mutually preferred but is acceptable to the mechanism that is not mutually preferred but is acceptable to the
target. target.
This protocol provides the following guarantees when per-message This protocol provides the following guarantees when per-message
integrity services are available on the established mechanism context integrity services are available on the established mechanism
and the mechanism list was altered by an adversary such that a context, and the mechanism list was altered by an adversary such that
mechanism which is not mutually preferred could be selected: a mechanism that is not mutually preferred could be selected:
a) If the last mechanism token is sent by the initiator, both peers a) If the last mechanism token is sent by the initiator, both peers
shall fail; shall fail;
b) If the last mechanism token is sent by the acceptor, the acceptor b) If the last mechanism token is sent by the acceptor, the acceptor
shall not complete and the initiator at worst shall complete with shall not complete and the initiator, at worst, shall complete
its preferred mechanism being selected. with its preferred mechanism being selected.
The negotiation may not be terminated if an alteration was made but The negotiation may not be terminated if an alteration was made but
it had no material impact. had no material impact.
The protection of the negotiation depends on the strength of the The protection of the negotiation depends on the strength of the
integrity protection. In particular, the strength of SPNEGO is no integrity protection. In particular, the strength of SPNEGO is no
stronger than the integrity protection of the weakest mechanism stronger than the integrity protection of the weakest mechanism
acceptable to GSS-API peers. acceptable to GSS-API peers.
Note that where there exist multiple mechanisms with similar context Note that where there exist multiple mechanisms with similar context
tokens, but different semantics, such that some or all of the tokens, but different semantics, such that some or all of the
mechanisms' context tokens can be easily altered so that one mechanisms' context tokens can be easily altered so that one
mechanism's context tokens may pass for another of the similar mechanism's context tokens may pass for another of the similar
mechanism's context tokens, then there may exist downgrade or similar mechanism's context tokens, then there may exist a downgrade or
attacks. For example, if a given family of mechanisms uses the same similar attacks. For example, if a given family of mechanisms uses
context token syntax for two or more variants and depends on the OID the same context token syntax for two or more variants and depends on
in the initial token's pseudo-ASN.1/DER wrapper, but does not provide the OID in the initial token's pseudo-ASN.1/DER wrapper, but does not
integrity protection for that OID, then there may exist an attack provide integrity protection for that OID, then there may exist an
against those mechanisms. SPNEGO does not generally defeat such attack against those mechanisms. SPNEGO does not generally defeat
attacks. such attacks.
In all cases, the communicating peers are exposed to the denial of In all cases, the communicating peers are exposed to the denial of
service threat. service threat.
8. IANA Considerations 8. Acknowledgments
This document has no actions for IANA.
9. Acknowledgments
The authors wish to thank Sam Hartman, Nicolas Williams, Ken Raeburn, The authors wish to thank Sam Hartman, Nicolas Williams, Ken Raeburn,
Martin Rex, Jeff Altman, Tom Yu, Cristian Ilac, Simon Spero and Bill Martin Rex, Jeff Altman, Tom Yu, Cristian Ilac, Simon Spero, and Bill
Sommerfeld for their comments and suggestions during development of Sommerfeld for their comments and suggestions during the development
this document. of this document.
Luke Howard provided a prototype of this protocol in Heimdal and Luke Howard provided a prototype of this protocol in Heimdal and
resolved several issues in the initial draft. resolved several issues in the initial version of this document.
Eric Baize and Denis Pinkas wrote the original SPNEGO specification Eric Baize and Denis Pinkas wrote the original SPNEGO specification
[RFC2478] of which some of the text has been retained in this [RFC2478] of which some of the text has been retained in this
document. document.
10. References 9. References
10.1 Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program [RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000. Interface Version 2, Update 1", RFC 2743, January 2000.
[X690] ASN.1 encoding rules: Specification of Basic Encoding [X690] ASN.1 encoding rules: Specification of Basic Encoding Rules
Rules (BER), Canonical Encoding Rules (CER) and (BER), Canonical Encoding Rules (CER) and Distinguished
Distinguished Encoding Rules (DER), ITU-T Recommendation Encoding Rules (DER), ITU-T Recommendation X.690 (1997) |
X.690 (1997) | ISO/IEC International Standard 8825-1:1998. ISO/IEC International Standard 8825-1:1998.
10.2 Informative References 9.2. Informative References
[RFC2478] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API [RFC2478] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API
Negotiation Mechanism", RFC 2478, December 1998. Negotiation Mechanism", RFC 2478, December 1998.
Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: lzhu@microsoft.com
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: paulle@microsoft.com
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: karthikj@microsoft.com
Wyllys Ingersoll
Sun Microsystems
1775 Wiehle Avenue, 2nd Floor
Reston, VA 20190
US
Email: wyllys.ingersoll@sun.com
Appendix A. SPNEGO ASN.1 Module Appendix A. SPNEGO ASN.1 Module
SPNEGOASNOneSpec { SPNEGOASNOneSpec {
iso(1) identified-organization(3) dod(6) internet(1) iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanism(5) snego (2) modules(4) spec2(2) security(5) mechanism(5) snego (2) modules(4) spec2(2)
} DEFINITIONS EXPLICIT TAGS ::= BEGIN } DEFINITIONS EXPLICIT TAGS ::= BEGIN
MechType ::= OBJECT IDENTIFIER MechType ::= OBJECT IDENTIFIER
-- OID represents each security mechanism as suggested by -- OID represents each security mechanism as suggested by
-- [RFC2743] -- [RFC2743]
skipping to change at page 25, line 7 skipping to change at page 17, line 12
sequenceFlag (3), sequenceFlag (3),
anonFlag (4), anonFlag (4),
confFlag (5), confFlag (5),
integFlag (6) integFlag (6)
} (SIZE (32)) } (SIZE (32))
END END
Appendix B. GSS-API Negotiation Support API Appendix B. GSS-API Negotiation Support API
In order to provide to a GSS-API caller (either the initiator or the In order to provide to a GSS-API caller (the initiator or the target
target or both) the ability to choose among the set of supported or both) with the ability to choose among the set of supported
mechanisms a reduced set of mechanisms for negotiation, two mechanisms, a reduced set of mechanisms for negotiation and two
additional APIs are defined: additional APIs are defined:
o GSS_Get_neg_mechs() indicates the set of security mechanisms o GSS_Get_neg_mechs() indicates the set of security mechanisms
available on the local system to the caller for negotiation, for available on the local system to the caller for negotiation, for
which appropriate credentials are available. which appropriate credentials are available.
o GSS_Set_neg_mechs() specifies the set of security mechanisms to be o GSS_Set_neg_mechs() specifies the set of security mechanisms to be
used on the local system by the caller for negotiation, for the used on the local system by the caller for negotiation, for the
given credentials. given credentials.
B.1 GSS_Set_neg_mechs call B.1. GSS_Set_neg_mechs Call
Inputs: Inputs:
o cred_handle CREDENTIAL HANDLE, -- NULL specifies default o cred_handle CREDENTIAL HANDLE, -- NULL specifies default
-- credentials -- credentials
o mech_set SET OF OBJECT IDENTIFIER o mech_set SET OF OBJECT IDENTIFIER
Outputs: Outputs:
o major_status INTEGER, o major_status INTEGER,
o minor_status INTEGER o minor_status INTEGER
Return major_status codes: Return major_status codes:
o GSS_S_COMPLETE indicates that the set of security mechanisms o GSS_S_COMPLETE indicates that the set of security mechanisms
available for negotiation has been set to mech_set. available for negotiation has been set to mech_set.
o GSS_S_FAILURE indicates that the requested operation could not be o GSS_S_FAILURE indicates that the requested operation could not be
performed for reasons unspecified at the GSS-API level. performed for reasons unspecified at the GSS-API level.
Allows callers to specify the set of security mechanisms that may be This allows callers to specify the set of security mechanisms that
negotiated with the credential identified by cred_handle. This call may be negotiated with the credential identified by cred_handle.
is intended for support of specialized callers who need to restrict This call is intended to support specialized callers who need to
the set of negotiable security mechanisms from the set of all restrict the set of negotiable security mechanisms from the set of
security mechanisms available to the caller (based on available all security mechanisms available to the caller (based on available
credentials). Note that if more than one mechanism is specified in credentials). Note that if more than one mechanism is specified in
mech_set, the order in which those mechanisms are specified implies a mech_set, the order in which those mechanisms are specified implies a
relative preference. relative preference.
B.2 GSS_Get_neg_mechs call B.2. GSS_Get_neg_mechs Call
Input: Input:
o cred_handle CREDENTIAL HANDLE -- NULL specifies default o cred_handle CREDENTIAL HANDLE -- NULL specifies default --
-- credentials credentials
Outputs: Outputs:
o major_status INTEGER, o major_status INTEGER,
o minor_status INTEGER, o minor_status INTEGER,
o mech_set SET OF OBJECT IDENTIFIER o mech_set SET OF OBJECT IDENTIFIER
Return major_status codes: Return major_status codes:
o GSS_S_COMPLETE indicates that the set of security mechanisms o GSS_S_COMPLETE indicates that the set of security mechanisms
skipping to change at page 26, line 18 skipping to change at page 18, line 25
Outputs: Outputs:
o major_status INTEGER, o major_status INTEGER,
o minor_status INTEGER, o minor_status INTEGER,
o mech_set SET OF OBJECT IDENTIFIER o mech_set SET OF OBJECT IDENTIFIER
Return major_status codes: Return major_status codes:
o GSS_S_COMPLETE indicates that the set of security mechanisms o GSS_S_COMPLETE indicates that the set of security mechanisms
available for negotiation has been returned in mech_set. available for negotiation has been returned in mech_set.
o GSS_S_FAILURE indicates that the requested operation could not be o GSS_S_FAILURE indicates that the requested operation could not be
performed for reasons unspecified at the GSS-API level. performed for reasons unspecified at the GSS-API level.
Allows callers to determine the set of security mechanisms available This allows callers to determine the set of security mechanisms
for negotiation with the credential identified by cred_handle. This available for negotiation with the credential identified by
call is intended for support of specialized callers who need to cred_handle. This call is intended to support specialized callers
reduce the set of negotiable security mechanisms from the set of who need to reduce the set of negotiable security mechanisms from the
supported security mechanisms available to the caller (based on set of supported security mechanisms available to the caller (based
available credentials). on available credentials).
Note: The GSS_Indicate_mechs() function indicates the full set of Note: The GSS_Indicate_mechs() function indicates the full set of
mechanism types available on the local system. Since this call has mechanism types available on the local system. Since this call has
no input parameter, the returned set is not necessarily available for no input parameter, the returned set is not necessarily available for
all credentials. all credentials.
Appendix C. Changes since RFC2478 Appendix C. Changes since RFC2478
SPNEGO implementations in Microsoft Windows 2000/Windows SPNEGO implementations in Microsoft Windows 2000/Windows XP/Windows
XP/Windows Server 2003 have the following behavior: no mechlistMIC Server 2003 have the following behavior: no mechlistMIC is produced
is produced and mechlistMIC is not processed if one is provided; and mechlistMIC is not processed if one is provided; if the initiator
if the initiator sends the last mechanism token, the acceptor will sends the last mechanism token, the acceptor will send back a
send back a negotiation token with an accept_complete state and no negotiation token with an accept_complete state and no mechlistMIC
mechlistMIC token. In addition, an incorrect OID token. In addition, an incorrect OID (1.2.840.48018.1.2.2) can be
(1.2.840.48018.1.2.2) can be used to identify the GSS-API Kerberos used to identify the GSS-API Kerberos Version 5 mechanism.
Version 5 mechanism.
The following changes have been made to be compatible with these The following changes have been made to be compatible with these
legacy implementations. legacy implementations.
* NegTokenTarg is changed to negTokenResp and it is the message * NegTokenTarg is changed to negTokenResp and is the message format
format for all subsequent negotiation tokens. for all subsequent negotiation tokens.
* NegTokenInit is the message for the initial negotiation message
and that message only. * NegTokenInit is the message for the initial negotiation message,
and only that message.
* mechTypes in negTokenInit is not optional. * mechTypes in negTokenInit is not optional.
* If the selected mechanism is also the most preferred mechanism
for both peers, it is safe to omit the MIC tokens. * If the selected mechanism is also the most preferred mechanism for
both peers, it is safe to omit the MIC tokens.
If at least one of the two peers implements the updated pseudo If at least one of the two peers implements the updated pseudo
mechanism in this document, the negotiation is protected. mechanism in this document, the negotiation is protected.
The following changes are to address problems in RFC 2478. The following changes are to address problems in RFC 2478.
* reqFlags is not protected therefore it should not impact the * reqFlags is not protected, therefore it should not impact the
negotiation. negotiation.
* DER encoding is required. * DER encoding is required.
* GSS_GetMIC() input is clarified. * GSS_GetMIC() input is clarified.
* Per-message integrity services are requested for the negotiated * Per-message integrity services are requested for the negotiated
mechanism. mechanism.
* Two MIC tokens are exchanged, one in each direction. * Two MIC tokens are exchanged, one in each direction.
An implementation that conforms to this specification will not An implementation that conforms to this specification will not
inter-operate with a strict 2748 implementation. Even if the new inter-operate with a strict RFC 2748 implementation. Even if the new
implementation always sends a mechlistMIC token, it will still fail implementation always sends a mechlistMIC token, it will still fail
to inter-operate. If it is a server, it will fail because it to inter-operate. If it is a server, it will fail because it
requests a mechlistMIC token using an option that older requests a mechlistMIC token using an option that older
implementations simply do not support. Clients will tend to fail as implementations do not support. Clients will tend to fail as well.
well.
As an alternative to the approach chosen in this specification, we As an alternative to the approach chosen in this specification, we
could have documented a correct behavior that is fully backward could have documented a correct behavior that is fully backward
compatible with RFC 2478 and included an appendix on how to compatible with RFC 2478 and included an appendix on how to inter-
inter-operate with existing incorrect implementations of RFC 2478. operate with existing incorrect implementations of RFC 2478.
As a practical matter, the SPNEGO implementers within the IETF have As a practical matter, the SPNEGO implementers within the IETF have
valued interoperability with the Microsoft implementations. We were valued interoperability with the Microsoft implementations. We were
unable to choose to maintain reasonable security guarantees, maintain unable to choose to maintain reasonable security guarantees, to
interoperability with the Microsoft implementations and maintain maintain interoperability with the Microsoft implementations, and to
interoperability with correct implementations of RFC 2478. The maintain interoperability with correct implementations of RFC 2478.
working group was not aware of any RFC 2478 implementations deployed
on the Internet. Even if there are such implementations, it is The working group was not aware of any RFC 2478 implementations
unlikely that they will inter-operate because of a critical flaw in deployed on the Internet. Even if there are such implementations, it
the description of the encoding of the mechanism list in RFC 2478. is unlikely that they will inter-operate because of a critical flaw
in the description of the encoding of the mechanism list in RFC 2478.
With the approach taken in this specification, security is ensured With the approach taken in this specification, security is ensured
between new implementations all the time while maintaining between new implementations all the time while maintaining
interoperability with the implementations deployed within the IETF interoperability with the implementations deployed within the IETF
community. The working group believes that this justifies breaking community. The working group believes that this justifies breaking
compatibility with a correct implementation of RFC 2478. compatibility with a correct implementation of RFC 2478.
Appendix D. mechListMIC Computation Example Appendix D. mechListMIC Computation Example
The following is an example to illustrate how the mechListMIC field The following is an example to illustrate how the mechListMIC field
skipping to change at page 30, line 5 skipping to change at page 21, line 8
MechTypeList data from the initiator's NegTokenInit token as input to MechTypeList data from the initiator's NegTokenInit token as input to
the GSS_GetMIC() function. In this case, the MIC would be computed the GSS_GetMIC() function. In this case, the MIC would be computed
over the following octets: over the following octets:
DER encoding of MechTypeList: DER encoding of MechTypeList:
30 nn 06 09 2A 86 48 86 F7 12 01 02 02 ... 30 nn 06 09 2A 86 48 86 F7 12 01 02 02 ...
Note that the identifier octet and length octet(s) for constructed Note that the identifier octet and length octet(s) for constructed
[0] (A0 nn) are not included in the MIC computation. [0] (A0 nn) are not included in the MIC computation.
Intellectual Property Statement Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
EMail: lzhu@microsoft.com
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
EMail: paulle@microsoft.com
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
EMail: karthikj@microsoft.com
Wyllys Ingersoll
Sun Microsystems
1775 Wiehle Avenue, 2nd Floor
Reston, VA 20190
US
EMail: wyllys.ingersoll@sun.com
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INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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