NETWORK WORKING GROUP N. Williams
Internet-Draft Sun
Expires: August 12, 2005 February 11, 2005
Extended Generic Security Service Mechanism Inquiry APIs
draft-ietf-kitten-extended-mech-inquiry-00.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
for use in mechanism composition, but also 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.
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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 Determination of Attribute Sets of Composite Mechs . . . . . 4
3.3 List of Known Mechanism Attributes . . . . . . . . . . . . . 4
3.4 Mechanism Attribute Sets of Existing Mechs . . . . . . . . . 7
3.5 New GSS-API Function Interfaces . . . . . . . . . . . . . . 8
3.5.1 GSS_Indicate_mechs_by_attr() . . . . . . . . . . . . . . . . 9
3.5.2 GSS_Inquire_attrs_for_mech() . . . . . . . . . . . . . . . . 9
3.5.3 GSS_Display_mech_attr() . . . . . . . . . . . . . . . . . . 10
3.5.4 New Major Status Values . . . . . . . . . . . . . . . . . . 10
3.5.5 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . 11
4. Requirements for Mechanism Designers . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11
6. Security considerations . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1 Normative . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.2 Normative . . . . . . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . 13
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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
3. New GSS-API Interfaces
GSS-API applications face, today, the problem of how to select from
multiple GSS-API mechanisms that may be available. For example,
applications that support mechanism negotiation directly often have
to be careful not to use SPNEGO to avoid two-layer mechanism
negotiation, but since SPNEGO may be indicated by
GSS_Indicate_mechs() and since there's no way to know that a
mechanism negotiates mechanisms other than to hardcode the OIDs of
such mechanisms, such applications must hardcode the SPNEGO OID.
This problem is likely to be exacerbated by the introduction of
composite mechanisms.
To address this problem 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
3.5.1, 3.5.2 and 3.5.3 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 as well as for the programmatic composition of mechanisms.
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.
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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, registration w/ IANA
TBD]
3.2 Determination of Attribute Sets of Composite Mechs
Each mechanism, composite or otherwise, has a set of mechanism
attributes that it supports as specified.
The mechanism attribute set of a composite mechanism is to be
determined by the top-most stackable pseudo-mechanism of the
composite according to its own attribute set and that of the
remainder of the composite mechanism stack below it.
It may well be that some composite mechanisms' attribute sets consist
of the union of those of their every component, however this need not
be the case and MUST NOT be assumed.
Every stackable pseudo-mechanism's specification MUST specify the
rules for determining the mechanism attribute set of mechanisms
composed by it.
3.3 List of Known Mechanism Attributes
+-------------------------+---------+--------------------------------+
| Mech Attr Name | OID Arc | Arc Name |
+-------------------------+---------+--------------------------------+
| GSS_C_MA_MECH_CONCRETE | (1) | concrete-mech |
| GSS_C_MA_MECH_STACKABLE | (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 |
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| 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_CBINDINGS_BIDI | (25) | channel-bindings-bidirectional |
| GSS_C_MA_CBINDINGS_NEGO | (26) | channel-bindings-negotiate |
| GSS_C_MA_PFS | (27) | pfs |
| GSS_C_MA_COMPRESS | (28) | compress |
| GSS_C_MA_CTX_TRANS | (29) | context-transfer |
| <reserved> | (30..) | |
+-------------------------+---------+--------------------------------+
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_STACKABLE | Indicates that a mech is a |
| | pseudo-mechanism. |
| GSS_C_MA_MECH_COMPOSITE | Indicates that a mech is a |
| | composite mechanism. |
| 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 |
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| | 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 initiator |
| | anonymity. |
| GSS_C_MA_AUTH_TARG_ANON | Indicates support for acceptor |
| | anonymity. |
| 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_CBINDINGS_BIDI | Indicates that acceptors |
| | unconditionally indicate to |
| | initiators whether their |
| | channel bindings were matched |
| | the acceptors', even when the |
| | acceptor applications use |
| | GSS_C_NO_CHANNEL_BINDINGS.. |
| GSS_C_MA_CBINDINGS_NEGO | Indicates that the mech acts as |
| | a signal for application |
| | support for and willingness to |
| | use channel bindings. |
| GSS_C_MA_PFS | Indicates support for Perfect |
| | Forward Security. |
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| 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
3.4 Mechanism Attribute Sets of Existing Mechs
The Kerberos V mechanism [RFC1964] [CFX] 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 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 offers the following attributes:
o GSS_C_MA_MECH_CONCRETE (should be stackable, but does not compose)
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
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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 [SPNEGO] 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.
3.5 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, what mechanisms provide what features and what
compositions are legal.
These new interfaces are all OPTIONAL.
In order to preserve backwards compatibility with applications that
do not use the new interfaces GSS_Indicate_mechs() MUST NOT indicate
support for any stackable pseduo-mechanisms. GSS_Indicate_mechs()
MAY indicate support for some, all or none of the available composite
mechanisms; which composite mechanisms, if any, are indicated through
GSS_Indicate_mechs() SHOULD be configurable. GSS_Acquire_cred() and
GSS_Add_cred() MUST NOT create credentials for composite mechanisms
not explicitly requested or, if no desired mechanism or mechanisms
are given, for composite mechanisms not indicated by
GSS_Indicate_mechs().
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, stackable
pseudo-mechanism and composite mechanisms).
Applications may use GSS_Inquire_attrs_for_mech() to test whether a
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given composite mechanism is available and the set of features that
it offers.
3.5.1 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.
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, stackable, etc...).
3.5.2 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
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(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).
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.
Because the mechanism attribute sets of composite mechanisms need not
be the union of their components', when called to obtain the feature
set of a composite mechanism GSS_Inquire_mech_attrs_for_mech()
obtains it by querying the mechanism at the top of the stack. See
Section 3.1.
3.5.3 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.
3.5.4 New Major Status Values
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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 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).
3.5.5 C-Bindings
#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
Stackable pseudo-mechanisms specifications MUST:
o list the set of GSS-API mechanism attributes associated with them
o list their initial mechanism composition rules
o specify a mechanism for updating their mechanism composition rules
All other 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
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with GSS_C_MA_* is reserved for allocation by the IANA.
Allocation of arcs in the namespace of OIDs relative to the base
mechanism attribute OID specified in Section 3.1 is reserved to the
IANA.
6. Security considerations
...
7. References
7.1 Normative
[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 Normative
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC
1964, June 1996.
[RFC2478] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API
Negotiation Mechanism", RFC 2478, December 1998.
Author's Address
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
EMail: Nicolas.Williams@sun.com
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