NETWORK WORKING GROUP N. Williams Internet-Draft Sun Expires: December 30, 2004 July 2004 A PRF API extension for the GSS-API
draft-ietf-kitten-gssapi-prf-01.txtdraft-ietf-kitten-gssapi-prf-02.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 30, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document defines a Pseudo-Random Function (PRF) extension to the Generic Security Service Applicatoin Programming Interface (GSS-API) for keying application protocols given an established GSS-API security context. The primary intended use of this function is to key secure session layers that don't or cannot use GSS-API per-message MIC (message integrity check) and wrap tokens for session protection. Table of Contents 1. Conventions used in this document . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 5 3.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 56 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 8 5.2 Informative References . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 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 A need has arisen for users of the GSS-API to key applications' cryptographic protocols using established GSS-API security contexts. Such applications can use the GSS-API for authentication, but not for transport security (for whatever reasons), and since the GSS-API does not provide a method for obtaining keying material from established security contexts such applications cannot make effective use of the GSS-API. To address this need we define a pseudo-random function (PRF) extension to the GSS-API. 3. GSS_Pseudo_random() Inputs: o context CONTEXT handle, o prf_in OCTET STRING, o desired_output_len INTEGER Outputs: o major_status INTEGER, o minor_status INTEGER, o prf_out OCTET STRING Return major_status codes: o GSS_S_COMPLETE indicates no error. o GSS_S_NO_CONTEXT indicates that a null context has been provided as input. o GSS_S_CONTEXT_EXPIRED indicates that an expired context has been provided as input. o GSS_S_UNAVAILABLE indicates that the mechanism lacks support for this function.function or, if the security context is not fully established, that the context is not ready to compute the PRF. o GSS_S_FAILURE indicates failure or lack of support; the minor status code may provide additional information. This function applies the established context's mechanism's keyed PRF function to the input data (prf_in), keyed with key material associated with the given security context and outputs the resulting octet string (prf_out) of desired_output_len length. The output string of this function MUST be a pseudo-random function [GGM1][GGM2] of the input keyed with key material from the established security context -- the chances of getting the same output given different input parameters should be exponentially small. This function, applied to the same inputs by an initiator and acceptor using the same established context, MUST produce the *same results* for both, the initiator and acceptor, even if called multiple times for the same context. Mechanisms MAY limit the output of the PRF according, possibly in ways related to the types of cryptographic keys available for the PRF function, thus the prf_out output of GSS_Pseudo_random() MAY be smaller than requested. Mechanisms may be able to compute PRFs with security contexts that are not fully established, therefore applications MAY call GSS_Pseudo_random() with such security contexts. Such mechanisms MUST return GSS_S_UNAVAILABLE when called on to compute a PRF given a security context that is not fully established and also not ready for PRF computation. Mechanisms that allow for PRF computation prior to full security context establishment MUST use the same PRF and key material, for any given security context, both, before and after full context establishment, and the PRF and key material negotiation MUT be authenticated when the security context is fully established. 3.1 C-Bindings OM_uint32 gss_pseudo_random( OM_uint32 *minor_status, gss_ctx_id_t context, const gss_buffer_t prf_in, ssize_t desired_output_len, gss_buffer_t prf_out ); 4. Security Considerations Care should be taken in properly designing a mechanism's PRF function. GSS mechanisms' PRF functions should use a key derived from contexts' session keys and should preserve the forward security properties of the mechanisms' key exchanges. Some mechanisms may support the GSS PRF function with security contexts that are not fully established, but applications MUST assume that authentication, mutual or otherwise, has not completed until the security context is fully established 5. References 5.1 Normative References [GGM1] Goldreich, O., Goldwasser, S. and S. Micali, "How to Construct Random Functions", October 1986. [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. 5.2 Informative References [GGM2] Goldreich, O., Goldwasser, S. and S. Micali, "On the Cryptographic Applications of Random Functions", 1985. [RFC1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994. Author's Address Nicolas Williams Sun Microsystems 5300 Riata Trace Ct Austin, TX 78727 US EMail: Nicolas.Williams@sun.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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