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
AbstractThe 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
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. 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
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. RFC2119].
Section 18.104.22.168 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.
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.
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. 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.
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. 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
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. 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.
GFD.024]. The "attrs" buffer set is de-allocated by the caller using gss_release_buffer_set().
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.
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 );
(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.
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 22.214.171.124.5.6.6.
[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. [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.
http://www.sunet.se Sam Hartman Painless Security EMail: email@example.com Simon Josefsson SJD AB Johan Olof Wallins Vaeg 13 171 64 Solna Sweden EMail: firstname.lastname@example.org URI: http://josefsson.org/