NFSv4 M. Eisler Internet-Draft NetApp Intended status: Standards Track February 24, 2008 Expires: August 27, 2008 RPCSEC_GSS Version 2 draft-ietf-nfsv4-rpcsec-gss-v2-02.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 August 27, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This Internet-Draft describes version 2 of the RPCSEC_GSS protocol. Version 2 is the same as Version 1 but adds support for channel bindings. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this Eisler Expires August 27, 2008 [Page 1] Internet-Draft RPCSEC_GSSv2 February 2008 document are to be interpreted as described in RFC 2119 [1]. Table of Contents 1. Introduction and Motivation . . . . . . . . . . . . . . . . . . 3 2. Channel Bindings Explained . . . . . . . . . . . . . . . . . . 3 3. The RPCSEC_GSSv2 Protocol . . . . . . . . . . . . . . . . . . . 4 3.1. Compatibility with RPCSEC_GSSv1 . . . . . . . . . . . . . . 4 3.2. New Version Number . . . . . . . . . . . . . . . . . . . . 4 3.3. New Procedure - RPCSEC_GSS_BIND_CHANNEL . . . . . . . . . . 5 3.4. New Security Service - rpc_gss_svc_channel_prot . . . . . . 6 4. Version Negotiation . . . . . . . . . . . . . . . . . . . . . . 6 5. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 9. Normative References . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Eisler Expires August 27, 2008 [Page 2] Internet-Draft RPCSEC_GSSv2 February 2008 1. Introduction and Motivation RPCSEC_GSS version 2 (RPCSEC_GSSv2) is the same as RPCSEC_GSS version 1 (RPCSEC_GSSv1) except that support for channel bindings has been added. The primary motivation for channel bindings is to securely take advantage of hardware assisted encryption that might exist at lower levels of the networking protocol stack, such as at the Internet Protocol (IP) layer in the form of IPsec. The secondary motivation is that even if lower levels are not any more efficient at encryption than the RPCSEC_GSS layer, if encryption is occurring at the lower level, it can be redundant at the RPCSEC_GSS level. Once an RPCSEC_GSS target and initiator are mutually assured that they are each using the same secure, end to end channel, the overhead of computing message integrity codes (MICs) for authenticating and integrity protecting RPC requests and replies can be eliminated because the channel is performing the same function. Similarly, if the channel also provides confidentiality, the overhead of RPCSEC_GSS privacy protect can also be eliminated. 2. Channel Bindings Explained If a channel between two parties is secure, there must be shared information between the two parties. This information might be secret or not. The requirement for secrecy depends on the specifics of the channel. For example, the shared information could be the concatenation of the public key of the source and destination of the channel (where each public key has a corresponding private key). Suppose the channel is not end-to-end, i.e. a man-in-the-middle (MITM) exists, and there are two channels, one from the initiator to the MITM, and one from the MITM to the target. The MITM cannot simply force each channel to use the same public keys, because the public keys come from private keys, and the key management system for each node will surely assign unique or random private keys. At most the MITM can force one end of each channel to use the same public key. The MIC of public keys from the initiator will not be verified by the target, because at least one of public keys will be different. Similarly, the MIC of the public keys from the target will not be verified by the initiator because at least one of the public keys will be different. A higher layer protocol using the secure channel can safely exploit the channel to the mutual benefit of the higher level parties if each higher level party can prove: Eisler Expires August 27, 2008 [Page 3] Internet-Draft RPCSEC_GSSv2 February 2008 o They each know the channel's shared information. o The proof of the knowledge of the shared information is in fact being conveyed by each of the higher level parties, and not some other entities. RPCSEC_GSSv2 simply adds an optional round trip that has the initiator compute a GSS MIC on the channel binding's shared information, and sends the MIC to the target. The target verifies the MIC, and in turn sends its own MIC of the shared information to the initiator which verifies the target's MIC. This accomplishes three things. First the initiator and target are mutually authenticated. Second, the initiator and target prove they know the channel's shared information, and thus are using the same channel. Third, the first and second things are done simultaneously. 3. The RPCSEC_GSSv2 Protocol The RPCSEC_GSSv2 protocol will now be explained. The entire protocol is not presented. Instead the differences between RPCSEC_GSSv2 and RPCSEC_GSSv1 are shown. 3.1. Compatibility with RPCSEC_GSSv1 The functionality of RPCSEC_GSSv1 is fully supported by RPCSEC_GSSv2. 3.2. New Version Number const RPCSEC_GSS_VERS_1 = 1; const RPCSEC_GSS_VERS_2 = 2; /* new */ struct rpc_gss_cred_t { union switch (unsigned int version) { /* version of RPCSEC_GSS */ case RPCSEC_GSS_VERS_1: case RPCSEC_GSS_VERS_2: /* new */ struct { rpc_gss_proc_t gss_proc; /* control procedure */ unsigned int seq_num; /* sequence number */ rpc_gss_service_t service; /* service used */ opaque handle<>; /* context handle */ } rpc_gss_cred_vers_1_t; As is apparent from the above, the RPCSEC_GSSv2 credential has the same format as the RPCSSEC_GSSv1 credential. By setting the version field to 2, this indicates that the initiator and target support channel bindings. Eisler Expires August 27, 2008 [Page 4] Internet-Draft RPCSEC_GSSv2 February 2008 3.3. New Procedure - RPCSEC_GSS_BIND_CHANNEL enum rpc_gss_proc_t { RPCSEC_GSS_DATA = 0, RPCSEC_GSS_INIT = 1, RPCSEC_GSS_CONTINUE_INIT = 2, RPCSEC_GSS_DESTROY = 3, RPCSEC_GSS_BIND_CHANNEL = 4 /* new */ }; struct rpc_gss_chan_bind_input { opaque rgcbi_chan_bindings<>; }; Once an RPCSEC_GSSv2 handle has been established over a secure channel, the client MAY issue RPCSEC_GSS_BIND_CHANNEL. Targets MUST support RPCSEC_GSS_BIND_CHANNEL. Like RPCSEC_GSS_INIT and RPCSEC_GSS_CONTINUE_INIT requests, the NULL RPC procedure MUST be used. Unlike those two requests, the arguments of the NULL procedure are not overloaded, because the verifier is of sufficient size for the purpose of RPCSEC_GSS_BIND_CHANNEL. The gss_proc field is set to RPCSEC_GSS_BIND_CHANNEL. The seq_num field is set as if gss_proc were set to RPCSEC_GSS_DATA. The service field is set to rpc_gss_svc_none. The handle field is set to that of an RPCSEC_GSS handle as returned by RPCSEC_GSS_INIT or RPCSEC_GSS_CONTINUE_INIT. When gss_proc is RPCSEC_GSS_DATA, the verifier of an RPC request is set to the output of GSS_GetMIC() on the RPC header as described in Section 5.3.1 of [2]. When gss_proc is RPCSEC_GSS_BIND_CHANNEL, the verifier of an RPC request is set to the output of GSS_GetMIC() on the concatenation of the RPC header ("up to and including the credential") and the XDR encoding of an instance of type data rpc_gss_chan_bind_input. Similarly when gss_proc is RPCSEC_GSS_DATA, the verifier of an RPC reply is set to the output of GSS_GetMIC() on the seq_num of the credential of the corresponding request (as described in Section 5.3.3.2 of [2]). When gss_proc is RPCSEC_GSS_BIND_CHANNEL, the verifier of an RPC reply is set to the ouput of GSS_GetMIC() on the concantenation of the seq_num and the XDR encoding of an instance of data type rpc_gss_chan_bind_input. The content of rpc_gss_chan_bind_input has a single field, rgcbi_chan_bindings. The rgcbi_chan_bindings field consists of channel bindings as defined in [3]. The channel bindings are a "canonical octet string encoding of the channel bindings", starting "with the channel bindings prefix followed by a colon (ASCII 0x3A)." Eisler Expires August 27, 2008 [Page 5] Internet-Draft RPCSEC_GSSv2 February 2008 Thus the channel bindings of the initiator are verified when the target verifies the verifier via GSS_VerifyMIC(). Similarly, the channel bindings of the target are verified when the initiator verifies the verifier of the RPC reply via GSS_VerifyMIC(). Errors are handled the same way as described in Section 5.3.3.4.2 of [2]. 3.4. New Security Service - rpc_gss_svc_channel_prot enum rpc_gss_service_t { /* Note: the enumerated value for 0 is reserved. */ rpc_gss_svc_none = 1, rpc_gss_svc_integrity = 2, rpc_gss_svc_privacy = 3, rpc_gss_svc_channel_prot = 4 /* new */ }; The rpc_gss_svc_channel_prot service is valid only if RPCSEC_GSSv2 is being used, an RPCSEC_GSS_BIND_CHANNEL procedure has been executed successfully, and the secure channel still exists. When rpc_gss_svc_channel_prot is used, the RPC requests and replies are similar to those of rpc_gss_svc_none except that the verifiers on the request and reply always have the flavor set to AUTH_NONE, and the contents are zero length. Note that even though NULL verifiers are used when rpc_gss_svc_channel_prot is used, non-NULL RPCSEC_GSS credentials are used. The same credential is used as before, except that service field is set to rpc_gss_svc_channel_prot. 4. Version Negotiation An initiator that supports version 2 of RPCSEC_GSS simply issues an RPCSEC_GSS request with the version field set to RPCSEC_GSS_VERS_2. If the target does not recognize RPCSEC_GSS_VERS_2, the target will return an RPC error per section 5.1 of [2]. The initiator MUST NOT attempt to use an RPCSEC_GSS handle returned by version 2 of a target with version 1 of the same target. The initiator MUST NOT attempt to use an RPCSEC_GSS handle returned by version 1 of a target with version 2 of the same target. 5. Implementation Notes Once a successful RPCSEC_GSS_BIND_CHANNEL procedure has been performed on an RPCSEC_GSSv2 context handle, the initiator's implementation may map application requests for rpc_gss_svc_none and Eisler Expires August 27, 2008 [Page 6] Internet-Draft RPCSEC_GSSv2 February 2008 rpc_gss_svc_integrity to rpc_gss_svc_channel_prot credentials. And if the secure channel has privacy enabled, requests for rpc_gss_svc_privacy can also be mapped to rpc_gss_svc_channel_prot. 6. Acknowledgements Nico Williams had the idea for extending RPCSEC_GSS to support channel bindings. 7. Security Considerations The security considerations are the same as [2]. 8. IANA Considerations None. 9. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [2] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol Specification", RFC 2203, September 1997. [3] Williams, N., "On the Use of Channel Bindings to Secure Channels", RFC 5056, November 2007. Author's Address Mike Eisler NetApp 5765 Chase Point Circle Colorado Springs, CO 80919 USA Phone: +1-719-599-9026 Email: email2mre-ietf@yahoo.com Eisler Expires August 27, 2008 [Page 7] Internet-Draft RPCSEC_GSSv2 February 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Eisler Expires August 27, 2008 [Page 8]