NETWORK WORKING GROUP N. Williams
Internet-Draft Sun
Expires: August 28, 2008 February 25, 2008
Extended Generic Security Service Mechanism Inquiry APIs
draft-ietf-kitten-extended-mech-inquiry-03.txt
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Copyright (C) The IETF Trust (2008).
Abstract
This document introduces new application programming interfaces
(APIs) to the Generic Security Services API (GSS-API) for extended
mechanism attribute inquiry. These interfaces are primarily intended
to reduce instances of hardcoding of mechanism identifiers in GSS
applications.
These interfaces include: mechanism attributes and attribute sets, a
function for inquiring the attributes of a mechanism, a function for
indicating mechanisms that posses given attributes, and a function
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for displaying mechanism attributes.
Table of Contents
1. Conventions used in this document . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
3. New GSS-API Interfaces . . . . . . . . . . . . . . . . . . 3
3.1. Mechanism Attributes and Attribute Sets . . . . . . . . . 3
3.2. List of Known Mechanism Attributes . . . . . . . . . . . . 4
3.3. Mechanism Attribute Sets of Existing Mechs . . . . . . . . 6
3.4. New GSS-API Function Interfaces . . . . . . . . . . . . . 7
3.4.1. GSS_Indicate_mechs_by_attr() . . . . . . . . . . . . . . . 8
3.4.2. GSS_Inquire_attrs_for_mech() . . . . . . . . . . . . . . . 8
3.4.3. GSS_Display_mech_attr() . . . . . . . . . . . . . . . . . 9
3.4.4. New Major Status Values . . . . . . . . . . . . . . . . . 9
3.4.5. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Requirements for Mechanism Designers . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 10
6. Security considerations . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . 12
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1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
GSS-API [RFC2743] mechanisms have a number of properties that may be
of interest to applications. The lack of APIs for inquiring about
available mechanisms' properties has meant that many GSS-API
applications must hardcode mechanism OIDs. Ongoing work may result
in a variety of new GSS-API mechanisms. Applications should not have
to hardcode their OIDs.
For example, the SSHv2 protocol [RFC4251] supports the use of GSS-API
mechanisms for authentication [RFC4462], but it explicitly prohibits
the use of SPNEGO [RFC4178]. Future mechanisms that negotiate
mechanisms would have to be forbidden as well, but there is no way to
implement applications that inquire what mechanisms are available and
then programmatically exclude mechanisms "like SPNEGO".
3. New GSS-API Interfaces
We introduce a new concept: that of mechanism attributes. By
allowing applications to query the set of attributes associated with
individual mechanisms and to find out which mechanisms support a
given set of attributes we allow applications to select mechanisms
based on their attributes yet without having to hardcode mechanism
OIDs.
Section 3.1 describes the mechanism attributes concept. Sections
3.4.1, 3.4.2 and 3.4.3 describe three new interfaces that deal in
mechanisms and attribute sets:
o GSS_Indicate_mechs_by_attrs()
o GSS_Inquire_attrs_for_mech()
o GSS_Display_mech_attr()
3.1. Mechanism Attributes and Attribute Sets
An abstraction for the features provided by pseudo-mechanisms is
needed in order to facilitate the programmatic selection of
mechanisms.
Two data types are needed: one for individual mechanism attributes
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and one for mechanism attribute sets. To simplify the mechanism
attributes interfaces we reuse the 'OID' and 'OID set' data types and
model individual mechanism attribute types as OIDs.
To this end we define an open namespace of mechanism attributes and
assign them arcs off of this OID:
<TBD> [1.3.6.1.5.5.12 appears to be available]
Each mechanism has a set of mechanism attributes that it supports as
described in its specification.
3.2. List of Known Mechanism Attributes
+-------------------------+---------+-------------------------+
| Mech Attr Name | OID Arc | Arc Name |
+-------------------------+---------+-------------------------+
| GSS_C_MA_MECH_CONCRETE | (1) | concrete-mech |
| GSS_C_MA_MECH_PSEUDO | (2) | pseudo-mech |
| GSS_C_MA_MECH_COMPOSITE | (3) | composite-mech |
| GSS_C_MA_MECH_NEGO | (4) | mech-negotiation-mech |
| GSS_C_MA_MECH_GLUE | (5) | mech-glue |
| GSS_C_MA_NOT_MECH | (6) | not-mech |
| GSS_C_MA_DEPRECATED | (7) | mech-deprecated |
| GSS_C_MA_NOT_DFLT_MECH | (8) | mech-not-default |
| GSS_C_MA_ITOK_FRAMED | (9) | initial-is-framed |
| GSS_C_MA_AUTH_INIT | (10) | auth-init-princ |
| GSS_C_MA_AUTH_TARG | (11) | auth-targ-princ |
| GSS_C_MA_AUTH_INIT_INIT | (12) | auth-init-princ-initial |
| GSS_C_MA_AUTH_TARG_INIT | (13) | auth-targ-princ-initial |
| GSS_C_MA_AUTH_INIT_ANON | (14) | auth-init-princ-anon |
| GSS_C_MA_AUTH_TARG_ANON | (15) | auth-targ-princ-anon |
| GSS_C_MA_DELEG_CRED | (16) | deleg-cred |
| GSS_C_MA_INTEG_PROT | (17) | integ-prot |
| GSS_C_MA_CONF_PROT | (18) | conf-prot |
| GSS_C_MA_MIC | (19) | mic |
| GSS_C_MA_WRAP | (20) | wap |
| GSS_C_MA_PROT_READY | (21) | prot-ready |
| GSS_C_MA_REPLAY_DET | (22) | replay-detection |
| GSS_C_MA_OOS_DET | (23) | oos-detection |
| GSS_C_MA_CBINDINGS | (24) | channel-bindings |
| GSS_C_MA_PFS | (25) | pfs |
| GSS_C_MA_COMPRESS | (26) | compress |
| GSS_C_MA_CTX_TRANS | (27) | context-transfer |
| <reserved> | (28..) | |
+-------------------------+---------+-------------------------+
Table 1
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+-------------------------+-----------------------------------------+
| Mech Attr Name | Purpose |
+-------------------------+-----------------------------------------+
| GSS_C_MA_MECH_CONCRETE | Indicates that a mech is neither a |
| | pseudo- mechanism nor a composite |
| | mechanism. |
| GSS_C_MA_MECH_PSEUDO | Indicates that a mech is a |
| | pseudo-mechanism. |
| GSS_C_MA_MECH_COMPOSITE | Indicates that a mech is a composite of |
| | other mechanisms. This is reserved for |
| | a specification of "stackable" |
| | pseudo-mechanisms. |
| GSS_C_MA_MECH_NEGO | Indicates that a mech negotiates other |
| | mechs (e.g., SPNEGO has this |
| | attribute). |
| GSS_C_MA_MECH_GLUE | Indicates that the OID is not for a |
| | mechanism but for the GSS-API itself. |
| GSS_C_MA_NOT_MECH | Indicates that the OID is known, yet |
| | also known not to be the OID of any |
| | GSS-API mechanism (or the GSS-API |
| | itself). |
| GSS_C_MA_DEPRECATED | Indicates that a mech (or its OID) is |
| | deprecated and MUST NOT be used as a |
| | default mechanism. |
| GSS_C_MA_NOT_DFLT_MECH | Indicates that a mech (or its OID) MUST |
| | NOT be used as a default mechanism. |
| GSS_C_MA_ITOK_FRAMED | Indicates that the given mechanism's |
| | initial context tokens are properly |
| | framed as per-section 3.1 of rfc2743. |
| GSS_C_MA_AUTH_INIT | Indicates support for authentication of |
| | initiator to acceptor. |
| GSS_C_MA_AUTH_TARG | Indicates support for authentication of |
| | acceptor to initiator. |
| GSS_C_MA_AUTH_INIT_INIT | Indicates support for "initial" |
| | authentication of initiator to |
| | acceptor. |
| GSS_C_MA_AUTH_TARG_INIT | Indicates support for initial |
| | authentication of acceptor to |
| | initiator. |
| GSS_C_MA_AUTH_INIT_ANON | Indicates support for |
| | GSS_C_NT_ANONYMOUS as an initiator |
| | principal name. |
| GSS_C_MA_AUTH_TARG_ANON | Indicates support for |
| | GSS_C_NT_ANONYMOUS as a target |
| | principal name. |
| GSS_C_MA_DELEG_CRED | Indicates support for credential |
| | delegation. |
| GSS_C_MA_INTEG_PROT | Indicates support for per-message |
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| | integrity protection. |
| GSS_C_MA_CONF_PROT | Indicates support for per-message |
| | confidentiality protection. |
| GSS_C_MA_MIC | Indicates support for MIC tokens. |
| GSS_C_MA_WRAP | Indicates support for WRAP tokens. |
| GSS_C_MA_PROT_READY | Indicates support for per-message |
| | protection prior to full context |
| | establishment. |
| GSS_C_MA_REPLAY_DET | Indicates support for replay detection. |
| GSS_C_MA_OOS_DET | Indicates support for out-of-sequence |
| | detection. |
| GSS_C_MA_CBINDINGS | Indicates support for channel bindings. |
| GSS_C_MA_PFS | Indicates support for Perfect Forward |
| | Security. |
| GSS_C_MA_COMPRESS | Indicates support for compression of |
| | data inputs to GSS_Wrap(). |
| GSS_C_MA_CTX_TRANS | Indicates support for security context |
| | export/import. |
+-------------------------+-----------------------------------------+
Table 2
3.3. Mechanism Attribute Sets of Existing Mechs
The Kerberos V mechanism [RFC1964] provides the following mechanism
attributes:
o GSS_C_MA_MECH_CONCRETE
o GSS_C_MA_ITOK_FRAMED
o GSS_C_MA_AUTH_INIT
o GSS_C_MA_AUTH_TARG
o GSS_C_MA_DELEG_CRED
o GSS_C_MA_INTEG_PROT
o GSS_C_MA_CONF_PROT
o GSS_C_MA_MIC
o GSS_C_MA_WRAP
o GSS_C_MA_PROT_READY
o GSS_C_MA_REPLAY_DET
o GSS_C_MA_OOS_DET
o GSS_C_MA_CBINDINGS
o GSS_C_MA_CTX_TRANS (some implementations, using implementation-
specific exported context token formats)
The Kerberos V mechanism also has a deprecated OID which has the same
mechanism attributes as above, and GSS_C_MA_DEPRECATED.
The mechanism attributes of the SPKM [RFC2025] family of mechanisms
will be provided in a separate document as SPKM is current being
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reviewed for possibly significant changes due to problems in its
specifications.
The LIPKEY mechanism [RFC2847] offers the following attributes:
o GSS_C_MA_MECH_CONCRETE
o GSS_C_MA_ITOK_FRAMED
o GSS_C_MA_AUTH_INIT_INIT
o GSS_C_MA_AUTH_TARG (from SPKM-3)
o GSS_C_MA_AUTH_TARG_ANON (from SPKM-3)
o GSS_C_MA_INTEG_PROT
o GSS_C_MA_CONF_PROT
o GSS_C_MA_REPLAY_DET
o GSS_C_MA_OOS_DET
o GSS_C_MA_CTX_TRANS (some implementations, using implementation-
specific exported context token formats)
(LIPKEY should also provide GSS_C_MA_CBINDINGS, but SPKM-3
requires clarifications on this point.)
The SPNEGO mechanism [RFC4178] provides the following attributes:
o GSS_C_MA_MECH_NEGO
o GSS_C_MA_ITOK_FRAMED
The attributes of mechanisms negotiated by SPNEGO are not modified by
the use of SPNEGO.
All other mechanisms' attributes will be described elsewhere.
3.4. New GSS-API Function Interfaces
Several new interfaces are given by which, for example, GSS-API
applications may determine what features are provided by a given
mechanism and what mechanisms provide what features.
These new interfaces are all OPTIONAL.
Applications should use GSS_Indicate_mechs_by_attr() instead of
GSS_Indicate_mechs() wherever possible.
Applications can use GSS_Indicate_mechs_by_attr() to determine what,
if any, mechanisms provide a given set of features.
GSS_Indicate_mechs_by_attr() can also be used to indicate (as in
GSS_Indicate_mechs()) the set of available mechanisms of each type
(concrete, mechanism negotiation pseudo-mechanism, etc.).
3.4.1. GSS_Indicate_mechs_by_attr()
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Inputs:
o desired_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_*
OIDs that the mechanisms indicated in the mechs output parameter
MUST offer.
o except_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_*
OIDs that the mechanisms indicated in the mechs output parameter
MUST NOT offer.
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o mechs SET OF OBJECT IDENTIFIER -- set of mechanisms that support
-- the desired_mech_attrs but not the except_mech_attrs.
Return major_status codes:
o GSS_S_COMPLETE indicates success; the output mechs parameter MAY
be the empty set (GSS_C_NO_OID_SET).
o GSS_BAD_MECH_ATTR indicates that at least one mechanism attribute
OID in desired_mech_attrs or except_mech_attrs is unknown to the
implementation.
o GSS_S_FAILURE indicates that the request failed for some other
reason.
GSS_Indicate_mechs_by_mech_attrs() returns the set of mechanism OIDs
that offer at least the desired_mech_attrs but none of the
except_mech_attrs.
When desired_mech_attrs and except_mech_attrs are the empty set this
function acts as a version of GSS_indicate_mechs() that outputs the
set of all supported mechanisms of all types. By setting the
desired_mechs input parameter to a set of a single GSS_C_MA_MECH*
feature applications can obtain the list of all supported mechanisms
of a given type (concrete, etc...).
3.4.2. GSS_Inquire_attrs_for_mech()
Inputs:
o mech OBJECT IDENTIFIER -- mechanism OID
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o mech_attrs SET OF OBJECT IDENTIFIER -- set of mech_attrs OIDs
(GSS_C_MA_*)
Return major_status codes:
o GSS_S_COMPLETE indicates success; the output mech_attrs parameter
MAY be the empty set (GSS_C_NO_OID_SET).
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o GSS_S_BAD_MECH indicates that the mechanism named by the mech
parameter does not exist or that mech is GSS_C_NO_OID and no
default mechanism could be determined.
o GSS_S_FAILURE indicates that the request failed for some other
reason.
GSS_Inquire_mech_attrs_for_mech() indicates the set of mechanism
attributes supported by a given mechanism.
3.4.3. GSS_Display_mech_attr()
Inputs:
o mech_attr OBJECT IDENTIFIER -- mechanism attribute OID
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o name OCTET STRING, -- name of mechanism attribute (e.g.,
GSS_C_MA_*)
o short_desc OCTET STRING, -- a short description of the mechanism
attribute
o long_desc OCTET STRING -- a longer description of the mechanism
attribute
Return major_status codes:
o GSS_S_COMPLETE indicates success.
o GSS_S_BAD_MECH_ATTR indicates that the mechanism attribute
referenced by the mech_attr parameter is unknown to the
implementation.
o GSS_S_FAILURE indicates that the request failed for some other
reason.
This function can be used to obtain human-readable descriptions of
GSS-API mechanism attributes.
3.4.4. New Major Status Values
A single new major status code is added for GSS_Display_mech_attr():
o GSS_S_BAD_MECH_ATTR
roughly corresponding to GSS_S_BAD_MECH, but applicable to mechanism
attribute OIDs, rather than to mechanism OIDs.
For the C-bindings of the GSS-API [RFC2744] GSS_S_BAD_MECH_ATTR shall
have a routine error number of 19 (this is shifted to the left by
GSS_C_ROUTINE_ERROR_OFFSET).
3.4.5. C-Bindings
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#define GSS_S_BAD_MECH_ATTR (19ul << GSS_C_ROUTINE_ERROR_OFFSET)
OM_uint32 gss_inquire_mechs_for_mech_attrs(
OM_uint32 *minor_status,
const gss_OID_set desired_mech_attrs,
gss_OID_set *mechs);
OM_uint32 gss_inquire_mech_attrs_for_mech(
OM_uint32 *minor_status,
const gss_OID mech,
gss_OID_set *mech_attrs);
OM_uint32 gss_display_mech_attr(
OM_uint32 *minor_status,
const gss_OID mech_attr,
gss_buffer_t name,
gss_buffer_t short_desc,
gss_buffer_t long_desc);
Figure 1
4. Requirements for Mechanism Designers
All future GSS-API mechanism specifications MUST:
o list the set of GSS-API mechanism attributes associated with them
5. IANA Considerations
The namsepace of programming language symbols with names beginning
with GSS_C_MA_* is reserved for allocation by IESG Protocol Action
(probably in the specifications of future GSS-API mechanisms).
6. Security considerations
This document specifies extensions to a security-related API. It
imposes new requirements on future GSS-API mechanisms, and the
specification of future protocols that use the GSS-API should make
reference to this document where applicable. The ability to inquire
about specific properties of mechanisms should improve security.
7. References
7.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2744] Wray, J., "Generic Security Service API Version 2 :
C-bindings", RFC 2744, January 2000.
7.2. Informative References
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC2025] Adams, C., "The Simple Public-Key GSS-API Mechanism
(SPKM)", RFC 2025, October 1996.
[RFC2847] Eisler, M., "LIPKEY - A Low Infrastructure Public Key
Mechanism Using SPKM", RFC 2847, June 2000.
[RFC4178] Zhu, L., Leach, P., Jaganathan, K., and W. Ingersoll, "The
Simple and Protected Generic Security Service Application
Program Interface (GSS-API) Negotiation Mechanism",
RFC 4178, October 2005.
[RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, January 2006.
[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,
"Generic Security Service Application Program Interface
(GSS-API) Authentication and Key Exchange for the Secure
Shell (SSH) Protocol", RFC 4462, May 2006.
Author's Address
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
Email: Nicolas.Williams@sun.com
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