KITTEN WORKING GROUP N. Williams
Internet-Draft Sun
Intended status: Standards Track L. Johansson
Expires: December 26, 2010 SUNET
June 24, 2010
GSS-API Naming Extensions
draft-ietf-kitten-gssapi-naming-exts-08.txt
Abstract
The Generic Security Services API (GSS-API) provides a simple naming
architecture that supports name-based authorization. This document
introduces new APIs that extend the GSS-API naming model to support
name attribute transfer between GSS-API peers.
Status of this Memo
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Table of Contents
1. Conventions used in this document . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
3. Name Attribute Authenticity . . . . . . . . . . . . . . . 3
4. Name Attributes/Values as ACL Subjects . . . . . . . . . . 4
5. Attribute Name Syntax . . . . . . . . . . . . . . . . . . 4
6. Mapping Mechanism Facilities to Name Attributes . . . . . 4
6.1. Kerberos V and SPKM Authorization-Data . . . . . . . . . . 5
6.2. PKIX . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.2.1. Standard PKIX Certificate Extensions . . . . . . . . . . . 5
6.2.2. Other PKIX Certificate Extensions and Attributes . . . . . 5
6.3. SAML attribute assertions . . . . . . . . . . . . . . . . 6
7. API . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. GSS_Display_name_ext() . . . . . . . . . . . . . . . . . . 6
7.1.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. GSS_Inquire_name() . . . . . . . . . . . . . . . . . . . . 7
7.2.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 7
7.3. GSS_Get_name_attribute() . . . . . . . . . . . . . . . . . 8
7.3.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 9
7.4. GSS_Set_name_attribute() . . . . . . . . . . . . . . . . . 9
7.4.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 10
7.5. GSS_Delete_name_attribute() . . . . . . . . . . . . . . . 11
7.5.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 11
7.6. GSS_Export_name_composite() . . . . . . . . . . . . . . . 11
7.6.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 14
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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
As described in [RFC4768] the GSS-API's naming architecture suffers
from certain limitations. This document proposes concrete GSS-API
extensions.
A number of extensions to the GSS-API [RFC2743] and its C Bindings
[RFC2744] are described herein. The goal is to make information
modeled as "name attributes" available to applications. Such
information MAY for instance be used by applications to make
authorization-decisions. For example, Kerberos V authorization data
elements, both in their raw forms, as well as mapped to more useful
value types, can be made available to GSS-API applications through
these interfaces.
The model is that GSS names have attributes. The attributes of a
name may be authenticated (eg an X509 attribute certificate or signed
SAML attribute assertion), or may have been set on a GSS name for the
purpose of locally "asserting" the attribute during credential
acquisition or security context exchange. Name attributes' values
are network representations thereof (e.g., the actual value octets of
the contents of an X.509 certificate extension, for example) and are
intended to be useful for constructing portable access control
facilities. Applications may often require language- or platform-
specific data types, rather than network representations of name
attributes, so a function is provided to obtain objects of such types
associated with names and name attributes.
3. Name Attribute Authenticity
An attribute is 'authenticated' iff there is a secure association
between the attribute (and its values) and the trusted source of the
peer credential. Examples of authenticated attributes are (any part
of) the signed portion of an X.509 certificate or AD-KDCIssued
authorization-data elements in Kerberos V Tickets provided of course
that the authenticity of the respective security associations (eg
signatures) have been verified.
Note that the fact that an attribute is authenticated does not imply
anything about the semantics of the attribute nor that the trusted
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credential source was authorized to assert the attribute. Such
interpretations SHOULD be the result of applying local policy to the
attribute.
An un-authentciated attribute is called _asserted_ in what
follows.This is not to be confused with other uses of the word
asserted or assertion eg "SAML attribute assertion", the attributes
of which may be authenticated in the sense of this document for
instance if the SAML attribute assertion was signed by a key trusted
by the peer.
4. Name Attributes/Values as ACL Subjects
To facilitate the development of portable applications that make use
of name attributes to construct and evaluate portable ACLs the GSS-
API makes name attribute values available in canonical network
encodings thereof.
5. Attribute Name Syntax
Attribute names are represented as opaque STRING elements in the API
described below. These attribute names have syntax and semantics
that are understood by the application and by the lower-layer
implementations (some of which are described below). In order to
present a consistent namespace to the application and at the same
time impose as few transformation requirements as possible to lower-
layer implementations attribute names SHOULD be URIs.
Technologies used in lower-layer protocols may of course use
attribute naming that are not based on URIs. Notably X.509
certificates will use OIDs for most naming purposes. In this case
OIDs MUST be mapped into URIs as described in [RFC3061] MUST be used.
If for example the OID 1.2.3 denotes an Extended Key Usage (cf
below), the corresponding GSS-API attribute name MUST be represented
as urn:oid:1.2.3.
6. Mapping Mechanism Facilities to Name Attributes
In this section we describe two important examples of lower-layer
implementations of this API. These examples are not mandatory to
implement and are only provided for reference. The use of [RFC2119]-
terms in this section is limited to those implementations of the GSS-
API naming extensions that choose to implement these lower-layer
technologies. Future mappings SHOULD be documented as RFCs.
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Kerberos V [RFC4120] and the Simple Public-Key GSS-API Mechanism,
SPKM described in [RFC2025], both support the concept and encoding of
containers of "authorization-data" as described in [RFC4120].
PKIX [RFC5280] supports a number of attribute-like features, like
Extended Key Usage values (EKUs) and certificate extensions.
6.1. Kerberos V and SPKM Authorization-Data
Authorization-data non-container elements asserted in Kerberos V AP-
REQ Authenticators MUST be mapped into *asserted* GSS-API name
attributes.
Authorization-data included in Kerberos V Tickets that is not
contained in AD-KDCIssued (with valid signature) MUST be mapped into
*asserted* GSS-API name attributes. Conversely, authorization-data
elements in Kerberos V Tickets contained by AD-KDCIssued MUST be
mapped into *authenticated* GSS-API name attributes.
6.2. PKIX
6.2.1. Standard PKIX Certificate Extensions
PKIX certificate extensions MAY/SHOULD/MUST (see comment above) be
represented as *authenticated* GSS-API name attributes named using
the _same_ OID mapped to a URN.
SubjectAltNames and Extended Key Usage OIDs, specifically, MUST be
represented as *authenticated* GSS-API name attributes; see below.
Certificate extensions MUST be represented as GSS-API name attributes
named using the OIDs used for the extensions (represented as URNs).
The value associated with Extended Key Usage attributes MUST have
NULL value represented as a zero-length OCTET STRING.
The standard PKIX certificate key usage (KUs, but not EKUs), MUST NOT
be represented as GSS-API name attributes.
PKIX certificate subjectAltNames MUST be mapped as *authenticated*
GSS-API name attributes. The values SHOULD be the values of the
subjectAltName represented as OCTET STRINGs if the type of the
subjectAltName supports a unique loss-less representation as string
values. Specifically dnsName, ipAddress, uniformResourceLocator and
emailAddress MUST be returned using the corresponding string
representation of those data types.
6.2.2. Other PKIX Certificate Extensions and Attributes
Any X.509 certificate extension not covered above SHOULD be
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represented as GSS-API name attributes with the OID of the X.509
extension and with OCTET STRING values containing the encoded value
of the extension.
6.3. SAML attribute assertions
Attributes contained in SAML attribute assertions MUST be mapped to
GSS-API name attributes with the same URIs as used in the SAML
attribute name.
SAML attributes found in SAML attribute assertions MUST NOT be mapped
as authenticated unless the SAML attribute assertion was signed by a
key trusted by the peer or otherwise protected from unauthorized
modification.
7. API
7.1. GSS_Display_name_ext()
Inputs:
o name NAME,
o display_as_name_type OBJECT IDENTIFIER
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o display_name STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_UNAVAILABLE indicates that the given name could not be
displayed using the syntax of the given name type.
o GSS_S_FAILURE indicates a general error.
This function displays a given name using the given name syntax, if
possible. This operation may require mapping MNs to generic name
syntaxes or generic name syntaxes to mechanism-specific name
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syntaxes; such mappings may not always be feasible and MAY be inexact
or lossy, therefore this function may fail.
7.1.1. C-Bindings
OM_uint32 GSS_Display_name_ext(
OM_uint32 *minor_status,
gss_name_t name,
gss_OID display_as_name_type,
gss_buffer_t display_name
);
7.2. GSS_Inquire_name()
Inputs:
o name NAME
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o name_is_MN BOOLEAN,
o mn_mech OBJECT IDENTIFIER,
o attrs SET OF OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates a general error.
This function outputs the set (represented as a NULL terminated array
of gss_buffer_t) of attributes of a name. It also indicates if a
given NAME is an MN or not and, if it is, what mechanism it's an MN
of. The gss_buffer_set_t type and associated API is defined in
[GFD.024]
7.2.1. C-Bindings
OM_uint32 gss_inquire_name(
OM_uint32 *minor_status,
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gss_name_t name,
int name_is_MN,
gss_OID *MN_mech,
gss_buffer_set_t *attrs
);
7.3. GSS_Get_name_attribute()
Inputs:
o name NAME,
o attr STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o authenticated BOOLEAN, -- TRUE iff authenticated by the trusted
peer credential source.
o complete BOOLEAN -- TRUE iff this represents a complete set of
values for the name.
o values SET OF OCTET STRING,
o display_values SET OF STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_UNAVAILABLE indicates that the given attribute OID is not
known or set.
o GSS_S_FAILURE indicates a general error.
This function outputs the value(s) associated with a given GSS name
object for a given name attribute.
The complete flag denotes that (if TRUE) the set of values represents
a complete set of values for this name. The peer being an
authoritative source of information for this attribute is a
sufficient condition for the complete flag to be set by the peer.
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In the federated case when several peers may hold some of the
attributes about a name this flag may be highly dangerous and SHOULD
NOT be used.
NOTE: This function relies on the GSS-API notion of "SET OF" allowing
for order preservation; this has been discussed on the KITTEN WG
mailing list and the consensus seems to be that, indeed, that was
always the intention. It should be noted however that the order
presented does not always reflect an underlying order of the
mechanism specific source of the attribute values.
7.3.1. C-Bindings
The C-bindings of GSS_Get_name_attribute() requires one function call
per-attribute value, for multi-valued name attributes. This is done
by using a single gss_buffer_t for each value and an input/output
integer parameter to distinguish initial and subsequent calls and to
indicate when all values have been obtained.
The 'more' input/output parameter should point to an integer variable
whose value, on first call to gss_name_attribute_get() MUST be -1,
and whose value upon function call return will be non-zero to
indicate that additional values remain, or zero to indicate that no
values remain. The caller should not modify this parameter after the
initial call. The status of the complete and authenticated flags
MUST NOT change between multiple calls to iterate over values for an
attribute.
OM_uint32 gss_get_name_attribute(
OM_uint32 *minor_status,
gss_name_t name,
gss_buffer_t attr,
int *authenticated,
int *complete,
gss_buffer_t value,
gss_buffer_t display_value,
int *more
);
7.4. GSS_Set_name_attribute()
Inputs:
o name NAME,
o complete BOOLEAN, -- TRUE iff this represents a complete set of
values for the name.
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o attr STRING,
o values SET OF OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_UNAVAILABLE indicates that the given attribute OID is not
known or could not be set.
o GSS_S_FAILURE indicates a general error.
The complete flag denotes that (if TRUE) the set of values represents
a complete set of values for this name. The peer being an
authoritative source of information for this attribute is a
sufficient condition for the complete flag to be set by the peer.
In the federated case when several peers may hold some of the
attributes about a name this flag may be highly dangerous and SHOULD
NOT be used.
NOTE: This function relies on the GSS-API notion of "SET OF" allowing
for order preservation; this has been discussed on the KITTEN WG
mailing list and the consensus seems to be that, indeed, that was
always the intention. It should be noted that underlying mechanisms
may not respect the given order.
7.4.1. C-Bindings
The C-bindings of GSS_Set_name_attribute() requires one function call
per-attribute value, for multi-valued name attributes -- each call
adds one value. To replace an attribute's every value delete the
attribute's values first with GSS_Delete_name_attribute().
OM_uint32 gss_set_name_attribute(
OM_uint32 *minor_status,
gss_name_t name,
int complete,
gss_buffer_t attr,
gss_buffer_t value
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);
7.5. GSS_Delete_name_attribute()
Inputs:
o name NAME,
o attr STRING,
Outputs:
o major_status INTEGER,
o minor_status INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_UNAVAILABLE indicates that the given attribute OID is not
known.
o GSS_S_UNAUTHORIZED indicates that a forbidden delete operation was
attempted eg deleting a negative attribute.
o GSS_S_FAILURE indicates a general error.
Deletion of negative authenticated attributes from NAME objects MUST
NOT be allowed and must result in a GSS_S_UNAUTHORIZED.
7.5.1. C-Bindings
OM_uint32 gss_delete_name_attribute(
OM_uint32 *minor_status,
gss_name_t name,
gss_buffer_t attr
);
7.6. GSS_Export_name_composite()
Inputs:
o name NAME
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Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o exp_composite_name OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates a general error.
This function outputs a token which can be imported with
GSS_Import_name(), using GSS_C_NT_COMPOSITE_EXPORT as the name type
and which preserves any name attribute information associated with
the input name (which GSS_Export_name() may well not). The token
format is no specified here as this facility is intended for inter-
process communication only; however, all such tokens MUST start with
a two-octet token ID, hex 04 02, in network byte order.
The OID for GSS_C_NT_COMPOSITE_EXPORT is <TBD>.
7.6.1. C-Bindings
OM_uint32 gss_export_name_composite(
OM_uint32 *minor_status,
gss_name_t name,
gss_buffer_t exp_composite_name
);
8. IANA Considerations
This document creates a namespace of GSS-API name attributes.
Attributes are named by URIs, so no single authority is technically
needed for allocation. However future deployment experience may
indicate the need for an IANA registry for URIs used to reference
names specified by IETF standards. It is expected that this will be
a registry of URNs but this document provides no further guidance on
this registry.
9. Security Considerations
This document extends the GSS-API naming model to include support for
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name attributes. The intention is that name attributes are to be
used as a basis for (among other things) authorization decisions or
personalization for applications relying on GSS-API security
contexts.
The security of the application may be critically dependent on the
security of the attributes. This document classifies attributes as
asserted or authenticated. Asserted (non-authenticated) attributes
MUST NOT be used if the attribute has security implications for the
application (eg authorization decisions) since asserted attributes
may easily be controlled by the peer directly.
It is important to understand the meaning of 'authenticated' in this
setting. Authenticated does not imply that any semantic of the
attribute is claimed to be true. The only implication is that a
trusted third party has asserted the attribute as opposed to the
attribute being asserte by the peer itself. Any additional semantics
is always the result of applying policy. For instance in a given
deployment the mail attribute of the subject may be authenticated and
sourced from an email system where 'authoritive' values are kept. In
another situations users may be allowed to modify their mail
addresses freely. In both cases the 'mail' attribute may be
authenticated by virtue of being included in signed SAML attribute
assertions or by other means authenticated by the underlying
mechanism.
When the underlying security mechanism does not provide a permanent
unique identity (eg anonymous kerberos) the GSS-API naming extensions
may be used to provide a replacement permanent unique identity
attribute which in this case may be unique for each peer party. This
is analogous to the SAML permanentIdentifier attribute and has
comparable security and privacy properties and implications.
10. References
10.1. Normative References
[GFD.024] Argonne National Laboratory, National Center for
Supercomputing Applications, Argonne National Laboratory,
and Argonne National Laboratory, "GSS-API Extensions",
GFD GFD.024, June 2004.
[RFC2025] Adams, C., "The Simple Public-Key GSS-API Mechanism
(SPKM)", RFC 2025, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
10.2. Informative References
[RFC3061] Mealling, M., "A URN Namespace of Object Identifiers",
RFC 3061, February 2001.
[RFC4768] Hartman, S., "Desired Enhancements to Generic Security
Services Application Program Interface (GSS-API) Version 3
Naming", RFC 4768, December 2006.
Authors' Addresses
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
Email: Nicolas.Williams@sun.com
Leif Johansson
Swedish University Network
Thulegatan 11
Stockholm
Sweden
Email: leifj@sunet.se
URI: http://www.sunet.se
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