GSS-API Naming
ExtensionsSun Microsystems5300 Riata Trace CtAustinTX78727USNicolas.Williams@sun.comSwedish University NetworkThulegatan 11StockholmSwedenleifj@sunet.sehttp://www.sunet.se
Security
KITTEN WORKING GROUPInternet-DraftThe 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.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 .As described in the GSS-API's
naming architecture suffers from certain limitations. This document
proposes concrete GSS-API extensions as outlined in .A number of extensions to the GSS-API
and its C Bindings 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.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
credential source authorized any one semantic of the attribute. Such
interpretations MAY 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 if the SAML
attribute assertion was signed by a key trusted by the peer.Some name attributes (e.g., numeric user or group identifiers) may be
useful as subjects of access control list (ACL) entries, some may not
(e.g., time of day login restrictions). The GSS_Inquire_name_attribute()
function indicates this.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.To facilitate the development of platform- or language-specific
applications that need access to native types of representations of name
attributes an optional facility is provided, GSS_Map_name_to_any().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.When mapping entities named by OIDs into this API MUST be used. For example if the OID 1.2.3
denotes an Extended Key Usage, the corresponding GSS-API attribute MUST
be represented as urn:oid:1.2.3.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 -terms in this section is limited to those
implementations of the GSS-API naming extensions that choose to
implement these lower-layer technologies.Kerberos V and the Simple Public-Key
GSS-API Mechanism, SPKM described in ,
both support the concept and encoding of containers of
"authorization-data" as described in .PKIX supports a number of
attribute-like features, like Extended Key Usage values (EKUs) and
certificate extensions.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.The URIs for authorization-data elements MUST be the
authorization-data elements 'ad-type' prefixed by the IANA-allocated
URN prefix (<TBD>)PKI certificate extensions MAY/SHOULD/MUST (see comment above) be
represented as authenticated GSS-API
name attributes named using the same.SubjectAltNames and EKUs, 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)Extended Key Usage extensions, specifically, MUST be mapped as
described above, except that GSS-API name attributes for EKUs MUST
have NULL values (i.e., zero-length OCTET STRINGs).PKI certificate key usages (KUs, but not EKUs), MUST NOT be
represented as GSS-API name attributes.PKI certificate subjectAltNames MUST be mapped as authenticated.Any X.509 certificate extension not covered above SHOULD be
represented as GSS-AOI name attributes with the OID of the X.509
extension and with OCTET STRING values containing the encoded value
of the extension.Attributes contained in SAML attribute assertions are mapped to
GSS-API name attributes with the same URIs as used in the SAML
attribute names (subject to representing OIDs to URIs).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.Inputs: name NAME,display_as_name_type OBJECT IDENTIFIEROutputs: major_status INTEGER,minor_status INTEGER,display_name STRINGReturn major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_UNAVAILABLE indicates that the given name could not be
displayed using the syntax of the given name type.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 syntaxes;
such mappings may not always be feasible and MAY be inexact or lossy,
therefore this function may fail.Inputs: name NAMEOutputs: major_status INTEGER,minor_status INTEGER,name_is_MN BOOLEAN,mn_mech OBJECT IDENTIFIER,asserted_attrs SET OF STRING,authenticated_attrs SET OF STRING,all_attrs SET OF STRING,Return major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_FAILURE indicates a general error.This function outputs the sets (represented as a NULL terminated
array of gss_buffer_t) of attributes of a name, that are authenticated
or asserted. It also indicates if a given NAME is an MN or not and, if
it is, what mechanism it's an MN of.Inputs: name NAME,attr STRINGOutputs: major_status INTEGER,minor_status INTEGER,authenticated BOOLEAN, -- TRUE iff authenticated by the trusted
peer credential source.complete BOOLEAN -- TRUE iff this represents a complete set of
values for the name.values SET OF OCTET STRING,display_values SET OF STRINGReturn major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_UNAVAILABLE indicates that the given attribute OID is not
known or set.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.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.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.Inputs: name NAME,complete BOOLEAN, -- TRUE iff this represents a complete set of
values for the name.attr STRING,values SET OF OCTET STRINGOutputs: major_status INTEGER,minor_status INTEGERReturn major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_UNAVAILABLE indicates that the given attribute OID is not
known or could not be set.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.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().Inputs: name NAME,attr STRING,Outputs: major_status INTEGER,minor_status INTEGERReturn major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_UNAVAILABLE indicates that the given attribute OID is not
known.GSS_S_UNAUTHORIZED indicates that a forbidden delete operation
was attempted eg deleting a negative attribute.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.Inputs: name NAMEOutputs: major_status INTEGER,minor_status INTEGER,exp_composite_name OCTET STRINGReturn major_status codes: GSS_S_COMPLETE indicates no error.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>.Inputs: name NAME,authenticated BOOLEAN, -- if TRUE only authenticated attributes
will be includedtype_id STRINGOutputs: major_status INTEGER,minor_status INTEGER,output ANY DEFINED BY type_idReturn major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_UNAVAILABLE indicates that the mapping or conversion
could not be done. The minor status code may provide additional
information.GSS_S_FAILURE indicates a general error. The minor status code
may provide additional information.Whereas name attribute's values are encoded in some network
representation applications often require native, language- and/or
platform-specific data types. This function provides access to such
types.Note the new C bindings type, gss_any_t. We define it as a
pointer to an incompletely declared struct.Inputs: name NAME,type_id STRING,input ANY DEFINED BY type_idOutputs: major_status INTEGER,minor_status INTEGER,Return major_status codes: GSS_S_COMPLETE indicates no error.GSS_S_UNAVAILABLE indicates that the mapping or conversion
could not be done. The minor status code may provide additional
information.GSS_S_FAILURE indicates a general error. The minor status code
may provide additional information.This function releases, if possible, the objects of language-
and/or platform-specific types output by GSS_Map_name_to_any(). If
such types have native release functions applications MAY use either
those or this function to release the given object.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.This document extends the GSS-API naming model to include support for
name attributes. The intention is that name attributes are to be used as
a basis for (among other things) authorization decisions or application
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. Only authenticated attributes MUST 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. It does not mean 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
'correct' values are kept. In another setting 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 lor 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 relying party. This is
analogous to the Liberty Alliance targetedID attribute and has similar
security implications.Desired Enhancements to GSSAPI Naming