NETWORK WORKING GROUP N. Williams
Internet-Draft Sun
Intended status: Standards Track March 25, 2009
Expires: September 26, 2009
Extended Generic Security Service Mechanism Inquiry APIs
draft-ietf-kitten-extended-mech-inquiry-05.txt
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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
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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
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. Mechanism Attribute Criticality . . . . . . . . . . . . . 8
3.4.2. GSS_Indicate_mechs_by_attr() . . . . . . . . . . . . . . . 8
3.4.3. GSS_Inquire_attrs_for_mech() . . . . . . . . . . . . . . . 9
3.4.4. GSS_Display_mech_attr() . . . . . . . . . . . . . . . . . 9
3.4.5. New Major Status Values . . . . . . . . . . . . . . . . . 10
3.4.6. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Requirements for Mechanism Designers . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 11
6. Security considerations . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . 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
3.4.2, 3.4.3 and 3.4.4 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 mechanisms and pseudo-
mechanisms is needed in order to facilitate the programmatic
selection of mechanisms. Pseudo-mechanisms are mechanisms which make
reference to other mechanisms in order to provide their services.
For example, SPNEGO is a pseudo-mechanism, for without other
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mechanisms SPNEGO is useless.
Two data types are needed: one for individual mechanism attributes
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:
<TBA by IANA> [1.3.6.1.5.5.13 appears to be available; see
http://www.iana.org/assignments/smi-numbers]
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) | wrap |
| 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 |
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| <reserved> | (28..) | |
+-------------------------+---------+-------------------------+
Table 1
+-------------------------+-----------------------------------------+
| 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. "Initial authentication" |
| | refers to the use of passwords, or keys |
| | stored on tokens, for authentication. |
| | Whether a mechanism supports initial |
| | authentication may depend on IETF |
| | consensus (see Security |
| | Considerations). |
| GSS_C_MA_AUTH_TARG_INIT | Indicates support for initial |
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| | 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 |
| | 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
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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
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
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.
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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. Mechanism Attribute Criticality
Mechanism attributes may be added at any time. Not only may
attributes be added to the list of known mechanism attributes at any
time, but the set of mechanism attributes supported by a mechanism
can be changed at any time.
For example, new attributes might be added to reflect whether a
mechanism's initiator must contact online infrastructure, and/or
whether the acceptor must do so. In this example the Kerberos V
mechanism would gain a new attribute even though the mechanism itself
is not modified.
Applications making use of attributes not defined herein then would
have no way of knowing whether a GSS-API implementation and its
mechanisms know about new mechanism attributes. To address this
problem GSS_Indicate_mechs_by_attr() and GSS_Indicate_mechs_by_attr()
support a notion of critical mechanism attributes. Applications can
search for mechanisms that understand mechanism attributes that are
critical to the application, and the application may ask what
mechanism attributes are understood by a given mechanism.
3.4.2. GSS_Indicate_mechs_by_attr()
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
o critical_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_*
OIDs that the mechanisms indicated in the mechs output parameter
MUST understand (i.e., mechs must know whether critical attributes
are or are not supported)
Outputs:
o major_status INTEGER
o minor_status INTEGER
o mechs SET OF OBJECT IDENTIFIER -- set of mechanisms that support
the given desired_mech_attrs but not the except_mech_attrs, and
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all of which understand the given critical_mech_attrs (the caller
must release this output with GSS_Release_oid_set())
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_S_FAILURE indicates that the request failed for some other
reason.
GSS_Indicate_mechs_by_attrs() returns the set of OIDs corresponding
to mechanisms that offer at least the desired_mech_attrs but none of
the except_mech_attrs, and which understand all of the attributes
listed in critical_mech_attrs.
When all three set of OID input parameters are the empty set this
function acts as a version of GSS_indicate_mechs() that outputs the
set of all supported mechanisms.
3.4.3. 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_*) supported by the mechanism (the caller must release
this output with GSS_Release_oid_set())
o known_mech_attrs SET OF OBJECT IDENTIFIER -- set of mech_attrs
OIDs known to the mechanism implementation (the caller must
release this output with GSS_Release_oid_set()).
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).
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.
3.4.4. GSS_Display_mech_attr()
Inputs:
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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 (the caller must release this output with
GSS_Release_buffer())
o long_desc OCTET STRING -- a longer description of the mechanism
attribute (the caller must release this output with
GSS_Release_buffer())
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.
3.4.5. 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).
3.4.6. C-Bindings
#define GSS_S_BAD_MECH_ATTR (19ul << GSS_C_ROUTINE_ERROR_OFFSET)
OM_uint32 gss_inquire_mechs_for_attrs(
OM_uint32 *minor_status,
const gss_OID_set desired_mech_attrs,
const gss_OID_set except_mech_attrs,
const gss_OID_set critical_mech_attrs,
gss_OID_set *mechs);
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OM_uint32 gss_inquire_attrs_for_mech(
OM_uint32 *minor_status,
const gss_OID mech,
gss_OID_set *mech_attrs,
gss_OID_set *known_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
Note that output buffers must be released via gss_release_buffer().
Output OID sets must be released via gss_release_oid_set().
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.
The IANA should allocate a base OID, as an arc of 1.3.6.1.5.5, for
the set of GSS_C_MA_* described herein, and it should register all of
the GSS_C_MA_* values described in Section 3.2
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.
The semantics of each mechanism attribute may include a security
component.
Application developers must understand that mechanism attributes may
be added at any time, both, to the set of known mechanism attributes,
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as well as to existing mechanism's sets of supported mechanism
attributes. Therefore application developers using the APIs
described herein must understand what mechanism attributes their
applications depend critically on, and must use the mechanism
attribute criticality features of these APIs.
7. References
7.1. Normative References
[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
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Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
Email: Nicolas.Williams@sun.com
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