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Internet Engineering Task Force (IETF) N. Williams
Request for Comments: 6680 Cryptonector, LLC
Category: Standards Track L. Johansson
ISSN: 2070-1721 SUNET
S. Hartman
Painless Security
S. Josefsson
SJD AB
August 2012
Generic Security Service Application Programming Interface (GSS-API)
Naming Extensions
Abstract
The Generic Security Service Application Programming Interface
(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
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6680.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
Williams, et al. Standards Track [Page 1]
RFC 6680 GSS-API Naming Extensions August 2012
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Name Attribute Authenticity . . . . . . . . . . . . . . . . . 4
4. Name Attributes/Values as ACL Subjects . . . . . . . . . . . . 4
5. Naming Contexts . . . . . . . . . . . . . . . . . . . . . . . 4
6. Representation of Attribute Names . . . . . . . . . . . . . . 6
7. API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. SET OF OCTET STRING . . . . . . . . . . . . . . . . . . . 7
7.2. Const Types . . . . . . . . . . . . . . . . . . . . . . . 8
7.3. GSS_Display_name_ext() . . . . . . . . . . . . . . . . . . 8
7.3.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 9
7.4. GSS_Inquire_name() . . . . . . . . . . . . . . . . . . . . 9
7.4.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 10
7.5. GSS_Get_name_attribute() . . . . . . . . . . . . . . . . . 10
7.5.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 11
7.6. GSS_Set_name_attribute() . . . . . . . . . . . . . . . . . 12
7.6.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 13
7.7. GSS_Delete_name_attribute() . . . . . . . . . . . . . . . 14
7.7.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 14
7.8. GSS_Export_name_composite() . . . . . . . . . . . . . . . 14
7.8.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . . 17
Williams, et al. Standards Track [Page 2]
RFC 6680 GSS-API Naming Extensions August 2012
1. Introduction
As described in [RFC4768], the GSS-API's naming architecture suffers
from certain limitations. This document attempts to overcome these
limitations.
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 (e.g., an X509 attribute certificate or
signed Security Assertion Markup Language (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.
Future updates of this specification may involve adding an attribute
namespace for attributes that only have application-specific
semantics. Note that mechanisms will still need to know how to
transport such attributes. The IETF may also wish to add functions
by which to inquire whether a mechanism(s) understands a given
attribute name or namespace and to list which attributes or attribute
namespaces a mechanism understands. Finally, the IETF may want to
consider adding a function by which to determine the name of the
issuer of a name attribute.
2. 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].
Williams, et al. Standards Track [Page 3]
RFC 6680 GSS-API Naming Extensions August 2012
3. Name Attribute Authenticity
An attribute is "authenticated" if and only if 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 (Section 5.2.6.2 of
[RFC4120]) in Kerberos V Tickets, provided, of course, that the
authenticity of the respective security associations (e.g.,
signatures) has 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 was authorized to assert the attribute. Such
interpretations SHOULD be the result of applying local policy to the
attribute.
An unauthenticated attribute is called _asserted_ in what follows.
This is not to be confused with other uses of the words "asserted" or
"assertion" such as "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 Access Control
Lists (ACLs), the GSS-API makes name attribute values available in
canonical network encodings thereof.
5. Naming Contexts
Several factors influence the context in which a name attribute is
interpreted. One is the trust context.
As discussed previously, applications apply local policy to determine
whether a particular peer credential issuer is trusted to make a
given statement. Different GSS-API mechanisms and deployments have
different trust models surrounding attributes they provide about a
name.
For example, Kerberos deployments in the enterprise typically trust a
Key Distribution Center (KDC) to make any statement about principals
in a realm. This includes attributes such as group membership.
Williams, et al. Standards Track [Page 4]
RFC 6680 GSS-API Naming Extensions August 2012
In contrast, in a federated SAML environment, the identity provider
typically exists in a different organization than the acceptor. In
this case, the set of group memberships or entitlements that the IDP
is permitted to make needs to be filtered by the policy of the
acceptor and federation.
So even an attribute containing the same information, such as email
address, would need to be treated differently by the application in
the context of an enterprise deployment from the context of a
federation.
Another aspect related to trust is the role of the credential issuer
in providing the attribute. Consider Public Key Cryptography for
Initial Authentication in Kerberos (PKINIT) [RFC4556]. In this
protocol, a public key and associated certificate are used to
authenticate to a Kerberos KDC. Consider how attributes related to a
PKINIT certificate should be made available in GSS-API
authentications based on the Kerberos ticket. In some deployments,
the certificate may be fully trusted; by including the certificate
information in the ticket, the KDC permits the acceptor to trust the
information in the certificate just as if the KDC itself had made
these statements. In other deployments, the KDC may have authorized
a hash of the certificate without evaluating the content of the
certificate or generally trusting the issuing certification
authority. In this case, if the certificate were included in the
issued ticket, the KDC would only be making the statement that the
certificate was used in the authentication. This statement would be
authenticated but would not imply that the KDC asserted that
particular attributes of the certificate accurately described the
initiator.
Another aspect of context is encoding of the attribute information.
An attribute containing an ASCII [ANSI.X3-4.1986] or UTF-8 [RFC3629]
version of an email address could not be interpreted the same as an
ASN.1 Distinguished Encoding Rules email address in a certificate.
All of these contextual aspects of a name attribute affect whether
two attributes can be treated the same by an application and thus
whether they should be considered the same name attribute. In the
GSS-API naming extensions, attributes that have different contexts
MUST have different names so they can be distinguished by
applications. As an unfortunate consequence of this requirement,
multiple attribute names will exist for the same basic information.
That is, there is no single attribute name for the email address of
an initiator. Other aspects of how mechanisms describe information
about subjects would already make this true. For example, some
mechanisms use OIDs to name attributes; others use URIs.
Williams, et al. Standards Track [Page 5]
RFC 6680 GSS-API Naming Extensions August 2012
Local implementations or platforms are likely to have sufficient
policy and information to know when contexts can be treated as the
same. For example, the GSS-API implementation may know that a
particular certification authority can be trusted in the context of a
PKINIT authentication. The local implementation may have sufficient
policy to know that a particular credential issuer is trusted to make
a given statement. In order to take advantage of this local
knowledge within the GSS-API implementation, naming extensions
support the concept of local attributes in addition to standard
attributes. For example, an implementation might provide a local
attribute for email address. The implementation would specify the
encoding and representation of this attribute; mechanism-specific
standards attributes would be re-encoded if necessary to meet this
representation. Only email addresses in contexts that meet the
requirements of local policy would be mapped into this local
attribute.
Such local attributes inherently expose a trade-off between
interoperability and usability. Using a local attribute in an
application requires knowledge of the local implementation. However,
using a standardized attribute in an application requires more
knowledge of policy and more validation logic in the application.
Sharing this logic in the local platform provides more consistency
across applications as well as reduces implementation costs. Both
options are needed.
6. Representation of Attribute Names
Different underlying mechanisms (e.g., SAML or X.509 certificates)
provide different representations for the names of their attributes.
In X.509 certificates, most objects are named by object identifiers
(OIDs). The type of object (certificate extension, name constraint,
keyPurposeID, etc.) along with the OID is sufficient to identify the
attribute. By contrast, according to Sections 8.2 and 2.7.3.1 of
[OASIS.saml-core-2.0-os], the name of an attribute has two parts.
The first is a URI describing the format of the name. The second
part, whose form depends on the format URI, is the actual name. In
other cases, an attribute might represent a certificate that plays
some particular role in a GSS-API mechanism; such attributes might
have a simple mechanism-defined name.
Attribute names MUST support multiple components. If there is more
than one component in an attribute name, the more significant
components define the semantics of the less significant components.
Williams, et al. Standards Track [Page 6]
RFC 6680 GSS-API Naming Extensions August 2012
Attribute names are represented as OCTET 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).
If an attribute name contains a space (ASCII 0x20), the first space
separates the most significant or primary component of the name from
the remainder. We may refer to the primary component of the
attribute name as the attribute name's "prefix". If there is no
space, the primary component is the entire name; otherwise, it
defines the interpretation of the remainder of the names.
If the primary component contains a ":" (ASCII 0x3a), then the
primary component is a URI. Otherwise, the attribute is a local
attribute and the primary component has meaning to the implementation
of GSS-API or to the specific configuration of the application.
Local attribute names with an "at" sign ("@") in them are reserved
for future allocation by the IETF.
Since attribute names are split at the first space into prefix and
suffix, there is a potential for ambiguity if a mechanism blindly
passes through a name attribute whose name it does not understand.
In order to prevent such ambiguities, the mechanism MUST always
prefix raw name attributes with a prefix that reflects the context of
the attribute.
Local attribute names under the control of an administrator or a
sufficiently trusted part of the platform need not have a prefix to
describe context.
7. API
7.1. SET OF OCTET STRING
The construct "SET OF OCTET STRING" occurs once in RFC 2743
[RFC2743], where it is used to represent a set of status strings in
the GSS_Display_status call. The Global Grid Forum has defined SET
OF OCTET STRING as a buffer set type in GFD.024 [GFD.024], which also
provides one API for memory management of these structures. The
normative reference to GFD.024 [GFD.024] is for the buffer set
functions defined in Section 2.5 and the associated buffer set C
types defined in Section 6 (namely gss_buffer_set_desc,
gss_buffer_set_t, gss_create_empty_buffer_set,
gss_add_buffer_set_member, gss_release_buffer_set). Nothing else
from GFD.024 is required to implement this document. In particular,
that document specifies changes to the behavior of existing GSS-API
Williams, et al. Standards Track [Page 7]
RFC 6680 GSS-API Naming Extensions August 2012
functions in Section 3: implementing those changes are not required
to implement this document. Any implementation of SET OF OCTET
STRING for use by this specification MUST preserve order.
7.2. Const Types
The C-bindings for the new APIs use some types from [RFC5587] to
avoid issues with the use of "const". The normative reference to
[RFC5587] is for the C types specified in Figure 1 of Section 3.4.6.
Nothing else from that document is required to implement this
document.
7.3. GSS_Display_name_ext()
Inputs:
o name INTERNAL NAME
o display_as_name_type OBJECT IDENTIFIER
Outputs:
o major_status INTEGER
o minor_status INTEGER
o display_name OCTET STRING -- caller must release with
GSS_Release_buffer()
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 Mechanism Names (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.
Williams, et al. Standards Track [Page 8]
RFC 6680 GSS-API Naming Extensions August 2012
7.3.1. C-Bindings
The display_name buffer is de-allocated by the caller with
gss_release_buffer.
OM_uint32 gss_display_name_ext(
OM_uint32 *minor_status,
gss_const_name_t name,
gss_const_OID display_as_name_type,
gss_buffer_t display_name
);
7.4. GSS_Inquire_name()
Inputs:
o name INTERNAL 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 -- the caller is responsible for de-
allocating memory using GSS_Release_buffer_set
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates a general error.
This function outputs the set of attributes of a name. It also
indicates if a given name is an Mechanism Name (MN) or not and, if it
is, the mechanism of which it's an MN.
Williams, et al. Standards Track [Page 9]
RFC 6680 GSS-API Naming Extensions August 2012
7.4.1. C-Bindings
OM_uint32 gss_inquire_name(
OM_uint32 *minor_status,
gss_const_name_t name,
int *name_is_MN,
gss_OID *MN_mech,
gss_buffer_set_t *attrs
);
The gss_buffer_set_t is used here as the C representation of SET OF
OCTET STRING. This type is used to represent a set of attributes and
is a NULL-terminated array of gss_buffer_t. The gss_buffer_set_t
type and associated API is defined in GFD.024 [GFD.024]. The "attrs"
buffer set is de-allocated by the caller using
gss_release_buffer_set().
7.5. GSS_Get_name_attribute()
Inputs:
o name INTERNAL NAME
o attr OCTET STRING
Outputs:
o major_status INTEGER
o minor_status INTEGER
o authenticated BOOLEAN -- TRUE if and only if authenticated by the
trusted peer credential source
o complete BOOLEAN -- TRUE if and only if this represents a complete
set of values for the name
o values SET OF OCTET STRING -- the caller is responsible for de-
allocating memory using GSS_Release_buffer_set
o display_values SET OF OCTET STRING -- the caller is responsible
for de-allocating memory using GSS_Release_buffer_set
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
Williams, et al. Standards Track [Page 10]
RFC 6680 GSS-API Naming Extensions August 2012
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.
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.
7.5.1. C-Bindings
The C-bindings of GSS_Get_name_attribute() require 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_get_name_attribute(), 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.
The output buffers "value" and "display_value" are de-allocated by
the caller using gss_release_buffer().
Williams, et al. Standards Track [Page 11]
RFC 6680 GSS-API Naming Extensions August 2012
OM_uint32 gss_get_name_attribute(
OM_uint32 *minor_status,
gss_const_name_t name,
gss_const_buffer_t attr,
int *authenticated,
int *complete,
gss_buffer_t value,
gss_buffer_t display_value,
int *more
);
7.6. GSS_Set_name_attribute()
Inputs:
o name INTERNAL NAME
o complete BOOLEAN -- TRUE if and only if this represents a complete
set of values for the name
o attr OCTET 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 NAME is not
known or could not be set.
o GSS_S_FAILURE indicates a general error.
When the given NAME object is an MN, this function MUST fail (with
GSS_S_FAILURE) if the mechanism for which the name is an MN does not
recognize the attribute name or the namespace it belongs to. This is
because name attributes generally have some semantics that mechanisms
must understand.
On the other hand, when the given name is not an MN, this function
MAY succeed even if none of the available mechanisms understand the
given attribute, in which subsequent credential acquisition attempts
Williams, et al. Standards Track [Page 12]
RFC 6680 GSS-API Naming Extensions August 2012
(via GSS_Acquire_cred() or GSS_Add_cred()) with the resulting name
MUST fail for mechanisms that do not understand any one or more name
attributes set with this function. Applications may wish to use a
non-MN, then acquire a credential with that name as the desired name.
The acquired credentials will have elements only for the mechanisms
that can carry the name attributes set on the name.
Note that this means that all name attributes are locally critical:
the mechanism(s) must understand them. The reason for this is that
name attributes must necessarily have some meaning that the mechanism
must understand, even in the case of application-specific attributes
(in which case the mechanism must know to transport the attribute to
any peer). However, there is no provision to ensure that peers
understand any given name attribute. Individual name attributes may
be critical with respect to peers, and the specification of the
attribute will have to indicate whether the mechanism's protocol or
the application is expected to enforce criticality.
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.
7.6.1. 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_const_name_t name,
int complete,
gss_const_buffer_t attr,
gss_const_buffer_t value
);
Williams, et al. Standards Track [Page 13]
RFC 6680 GSS-API Naming Extensions August 2012
7.7. GSS_Delete_name_attribute()
Inputs:
o name INTERNAL NAME
o attr 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 NAME is not
known.
o GSS_S_UNAUTHORIZED indicates that a forbidden delete operation was
attempted, such as 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.
7.7.1. C-Bindings
OM_uint32 gss_delete_name_attribute(
OM_uint32 *minor_status,
gss_const_name_t name,
gss_const_buffer_t attr
);
7.8. GSS_Export_name_composite()
Inputs:
o name INTERNAL NAME
Outputs:
o major_status INTEGER
o minor_status INTEGER
Williams, et al. Standards Track [Page 14]
RFC 6680 GSS-API Naming Extensions August 2012
o exp_composite_name OCTET STRING -- the caller is responsible for
de-allocating memory using GSS_Release_buffer
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates a general error.
This function outputs a token that can be imported with
GSS_Import_name(), using GSS_C_NT_COMPOSITE_EXPORT as the name type
and that preserves any name attribute information (including the
authenticated/complete flags) associated with the input name (which
GSS_Export_name() may well not). The token format is not 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 1.3.6.1.5.6.6.
7.8.1. C-Bindings
The "exp_composite_name" buffer is de-allocated by the caller with
gss_release_buffer.
OM_uint32 gss_export_name_composite(
OM_uint32 *minor_status,
gss_const_name_t name,
gss_buffer_t exp_composite_name
);
8. IANA Considerations
IANA has registered a new name-type OID in "SMI Security for Name
System Designators Codes (nametypes)":
6 gss-composite-export [RFC6680]
(The absolute OID is 1.3.6.1.5.6.6.)
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.
Williams, et al. Standards Track [Page 15]
RFC 6680 GSS-API Naming Extensions August 2012
9. Security Considerations
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
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 (e.g., 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 asserted by the peer itself. Any additional
semantics are 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 "authoritative"
values are kept. In another situation, 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 (e.g., anonymous Kerberos), GSS-API naming extensions
may be used to provide a permanent unique identity attribute. This
may be a globally unique identifier, a value unique within the
namespace of the attribute issuer, or a "directed" identifier that is
unique per peer acceptor identity. SAML, to use one example
technology, offers a number of built-in constructs for this purpose,
such as a <NameID> with a Format of
"urn:oasis:names:tc:SAML:2.0:nameid-format:persistent". SAML
deployments also typically make use of domain-specific attribute
types that can serve as identifiers.
Williams, et al. Standards Track [Page 16]
RFC 6680 GSS-API Naming Extensions August 2012
10. References
10.1. Normative References
[GFD.024] Meder, S., Welch, V., Tuecke, S., and D. Engert, "GSS-API
Extensions", Global Grid Forum GFD.024, June 2004,
<http://www.ggf.org/documents/GFD.24.pdf>.
[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.
[RFC5587] Williams, N., "Extended Generic Security Service Mechanism
Inquiry APIs", RFC 5587, July 2009.
10.2. Informative References
[ANSI.X3-4.1986]
American National Standards Institute, "Coded Character
Set - 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
[RFC4768] Hartman, S., "Desired Enhancements to Generic Security
Services Application Program Interface (GSS-API) Version 3
Naming", RFC 4768, December 2006.
Williams, et al. Standards Track [Page 17]
RFC 6680 GSS-API Naming Extensions August 2012
Authors' Addresses
Nicolas Williams
Cryptonector, LLC
EMail: nico@cryptonector.com
Leif Johansson
Swedish University Network
Thulegatan 11
Stockholm
Sweden
EMail: leifj@sunet.se
URI: http://www.sunet.se
Sam Hartman
Painless Security
EMail: hartmans-ietf@mit.edu
Simon Josefsson
SJD AB
Johan Olof Wallins Vaeg 13
171 64 Solna
Sweden
EMail: simon@josefsson.org
URI: http://josefsson.org/
Williams, et al. Standards Track [Page 18]