One document matched: draft-ietf-nfsv4-rpcsec-gss-v2-00.txt
NFSv4 M. Eisler
Internet-Draft NetApp
Intended status: Standards Track February 18, 2008
Expires: August 21, 2008
RPCSEC_GSS Version 2
draft-ietf-nfsv4-rpcsec-gss-v2-00.txt
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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
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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. New Version Number . . . . . . . . . . . . . . . . . . . . 4
3.2. New Procedure - RPCSEC_GSS_BIND_CHANNEL . . . . . . . . . . 5
3.3. New Security Service - rpc_gss_svc_channel_prot . . . . . . 6
4. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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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 a shared
secret known between the two parties. Either this secret is an
inherent part of the channel, or, because the channel is secure, and
has the option of confidentiality, the secret can be exchanged at any
time. 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:
o They each know the channel's shared secret.
o The proof of the knowledge of the shared secret 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 secret, and send
the MIC to the target. The target verifies the MIC, and in turn
sends its own MIC of the secret back 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 secret, and
thus are using the same channel. Third, the first and second thing
are done simultaneously.
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3. The RPCSEC_GSSv2 Protocol
The RPCSEC_GSSv2 protocol is now explained. The entire protocol is
not presented. Instead the differences between RPCSEC_GSSv2 and
RPCSEC_GSSv1 are shown.
3.1. 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.
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3.2. 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 {
unsigned int rgcbi_seq_num;
opaque rgcbi_chan_bindings<>;
};
struct rpc_gss_bind_channel_arg {
int rgbca_chan_bind_type;
opaque rgbca_MIC_hdr<>;
opaque rgbca_MIC_chan_bindings<>;
};
struct rpc_gss_bind_channel_res {
opaque rgbcr_MIC_seq<>;
opaque rgbcr_MIC_chan_bind<>;
};
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 argument and result of
RPCSEC_GSS_BIND_CHANNEL will fit in the RPC verifier. Like
RPCSEC_GSS_DATA, the seq_num field is set as if the procedure was
RPCSEC_GSS_DATA. The service is set to rpc_gss_svc_none, and the
handle is set to that of established RPCSEC_GSS handle. The
argument, of data type rpc_gss_bind_channel_arg is placed in the
request's verifier, with the RPC flavor set to RPCSEC_GSS. The field
rgbca_chan_bind_type identifies the type of channel binding the
client is using. The field rgbca_MIC_hdr is the GSS_GetMIC()
resulted of the RPC header (up to and including the credential. The
field rgbca_MIC_chan_bindings is equal to the result of GSS_GetMIC()
a value of data type rpc_gss_chan_bind_input.
The content of rpcs_gss_chan_bind_input is composed as follows. The
field rgcbi_seq_num is the same as the seq_num in the credential.
The field rgcbi_chan_bindings contains the actual channel bindings.
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If the target verifies rgbca_MIC_hdr, then it will return a result.
Otherwise an RPC level error is returned. See section 5.3.3.4.2 of
[2]. If the target does not recognize rgbca_chan_bind_type, it will
return a zero length rgbcr_MIC_chan_bind. If the target fails to
verify rgbca_MIC_chan_bindings, it will return an error as per
section 5.3.3.4.2 of [2].
The result pf RPCSEC_GSS_BIND_CHANNEL is returned in
rpc_gss_bind_channel_res in the RPC verifier of the reply. The
flavor of the verifier is set to RPCSEC_GSS. The field rgbcr_MIC_seq
is the result of the target's execution of GSS_GetMIC() on the
seq_num in the credential. The field rgbcr_MIC_chan_bind is the
result of the target's execution of GSS_GetMIC() on the a value of
data type rpc_gss_chan_bind_input. After the client successfully
verifies both MICs, the RPCSEC_GSS context is now associated with the
secure channel.
3.3. 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.
4. 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
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.
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5. Acknowledgements
Nico Williams had the idea for extending RPCSEC_GSS to support
channel bindings.
6. Security Considerations
The security considerations are the same as [2].
7. IANA Considerations
The rgbca_chan_bind_type field of the RPCSEC_GSS_BIND_CHANNEL
arguments requires an IANA registry. Values less than zero, are
reserved for experimentation, and do not have to be registered.
Values greater than or equal to zeor should be registered with IANA
in order to enable interoperability. An entry in the registry must
include the 32 bit binding type, and a reference to an RFC that
describes the channel and its bindings, including how the bindings
are constructed.
8. 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.
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
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