Network Working Group M. Eisler
Internet-Draft Network Appliance, Inc.
N. Williams
Sun Microsystems, Inc.
July 2004
The Channel Conjunction Mechanism (CCM) for GSS
draft-ietf-nfsv4-ccm-03
Status of this Memo
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ABSTRACT
This document describes a suite of new mechanisms under the GSS
[RFC2743]. Some protocols, such as RPCSEC_GSS [RFC2203], use GSS to
authenticate every message transfer, thereby incurring significant
overhead due to the costs of cryptographic computation. While
hardware-based cryptographic accelerators can mitigate such overhead,
it is more likely that acceleration will be available for lower layer
protocols, such as IPsec [RFC2401] than for upper layer protocols
like RPCSEC_GSS. CCM can be used as a way to allow GSS mechanism-
independent upper layer protocols to leverage the data stream
protections of lower layer protocols, without the inconvenience of
modifying the upper layer protocol to do so.
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TABLE OF CONTENTS
1. Conventions Used in this Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Example Application of CCM . . . . . . . . . . . . . . . . . 4
3.2. A Suite of CCM Mechanisms . . . . . . . . . . . . . . . . . . 4
3.3. QOPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Token Formats . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Mechanism Object Identifier . . . . . . . . . . . . . . . . . 5
4.2. Tokens for the CCM-BIND mechanisms . . . . . . . . . . . . . 6
4.2.1. Context Establishment Tokens for CCM-BIND Mechanisms . . . 6
4.2.1.1. Initial Context Token for CCM-BIND . . . . . . . . . . . 6
4.2.1.2. Subsequent Context Tokens for CCM-BIND . . . . . . . . . 6
4.2.2. Post Context Establishment Token Formats . . . . . . . . . 8
4.2.2.1. MIC Token for CCM-BIND . . . . . . . . . . . . . . . . . 9
4.2.2.2. Wrap Token for CCM-BIND . . . . . . . . . . . . . . . . . 9
4.2.3. Other Tokens for CCM-BIND . . . . . . . . . . . . . . . . . 9
4.3. Tokens for CCM-MIC . . . . . . . . . . . . . . . . . . . . . 9
4.3.1. Context Establishment Tokens for CCM-MIC . . . . . . . . . 9
4.3.1.1. Initial Context Token for CCM-MIC . . . . . . . . . . . . 9
4.3.1.2. Subsequent Context Tokens for CCM-MIC . . . . . . . . . 11
4.3.1.2.1. Subsequent Initiator Context Token for CCM-MIC . . . 11
4.3.1.2.2. Response Token for CCM-MIC . . . . . . . . . . . . . 11
4.3.2. MIC Token for CCM-MIC . . . . . . . . . . . . . . . . . . 13
4.3.3. Wrap Token for CCM-MIC . . . . . . . . . . . . . . . . . 13
4.3.4. Context Deletion Token . . . . . . . . . . . . . . . . . 13
4.3.5. Exported Context Token . . . . . . . . . . . . . . . . . 13
4.3.6. Other Tokens for CCM-MIC . . . . . . . . . . . . . . . . 13
5. Implementation Issues . . . . . . . . . . . . . . . . . . . . 13
5.1. Management of ccmMicCcmBindCtxHandle . . . . . . . . . . . 14
5.2. CCM-BIND Versus CCM-MIC . . . . . . . . . . . . . . . . . . 14
5.3. Initiating CCM-MIC Contexts . . . . . . . . . . . . . . . . 14
5.4. Accepting CCM-MIC Contexts . . . . . . . . . . . . . . . . 16
5.5. Non-Token Generating GSS-API Routines . . . . . . . . . . . 16
5.6. CCM-MIC and GSS_Delete_sec_context() . . . . . . . . . . . 16
5.7. GSS Status Codes . . . . . . . . . . . . . . . . . . . . . 16
5.7.1. Status Codes for CCM-BIND . . . . . . . . . . . . . . . . 16
5.7.2. Status Codes for CCM-MIC . . . . . . . . . . . . . . . . 17
5.7.2.1. CCM-MIC: GSS_Accept_sec_context() status codes . . . . 17
5.7.2.2. CCM-MIC: GSS_Init_sec_context() status codes . . . . . 18
6. Advice for NFSv4 Implementors . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. CCM XDR Description . . . . . . . . . . . . . . . . . . . . . 22
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
11. Normative References . . . . . . . . . . . . . . . . . . . . 25
12. Informative References . . . . . . . . . . . . . . . . . . . 26
13. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 27
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14. IPR Notices . . . . . . . . . . . . . . . . . . . . . . . . 27
15. Copyright Notice . . . . . . . . . . . . . . . . . . . . . . 28
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
The GSS framework provides a general means for authenticating clients
and servers, as well as providing a general means for encrypting and
integrity protecting data exchanged during a session. GSS specifies
formats for a set of tokens for authentication, integrity, and
privacy. The formats consist of a mechanism independent form, and a
mechanism dependent form. An example of a set of mechanism dependent
forms is the Kerberos V5 mechanism definition [RFC1964].
It is possible for a protocol to use GSS for one time authentication,
or for per message authentication. An example of the former is DAFS
[DAFS]. An example of the latter is RPCSEC_GSS. Obviously, it is
more secure to authenticate each message. On the other hand, it is
also more expensive. However, suppose the data stream of the upper
layer protocol (the layer using GSS) is protected at a lower layer
protocol from tampering, such as via a cryptographic checksum. If
so, it may not be necessary to additionally authenticate each message
of the upper layer protocol. Instead, it may suffice to use GSS to
authenticate at the beginning of the upper layer protocol's session.
To take advantage of one time authentication, existing consumers of
GSS that authenticate exclusively on each message have to change.
One way to change is to modify the protocol that is using GSS. This
has disadvantages including, introducing a protocol incompatibility,
and effectively introducing another authentication paradigm. Another
way to change, is the basis of the proposal in this document: the
Channel Conjunction Mechanism (CCM). CCM allows a GSS initiator and
target to conjunct (bind) a secure session (or channel) at one
protocol layer with (e.g. IPsec) a security context of a non-CCM GSS
mechanism. Since CCM is yet another mechanism under the GSS, the
effect is that there are no modifications to the protocol the GSS
consumer is using.
3. Overview
CCM is a "wrapper" mechanism over the set of all other GSS
mechanisms. When CCM creates a context, it invokes an underlying
mechanism to create a child context. CCM determines the underlying
mechanism by examining the mechanism object identifier (OID) that it
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is called with. The prefix will always be the OID of CCM, and the
suffix will be the OID of the underlying mechanism. The context
initiation and acceptance entry points of CCM wrap the resulting the
context tokens with a CCM header.
3.1. Example Application of CCM
Let us use RPCSEC_GSS and NFSv4 [RFC3530] as our example. Basic
understanding of the RPCSEC_GSS protocol is assumed. If an NFSv4
client uses the wrong security mechanism, the server returns the
NFS4ERR_WRONGSEC error. The client can then use NFSv4's SECINFO
operation to ask the server which GSS mechanism to use.
Let us say the client and server are using Kerberos V5 [RFC1964] to
secure the traffic. Suppose the TCP connection NFSv4 uses is secured
and encrypted with IPsec. It is therefore not necessary for
NFSv4/RPCSEC_GSS to use integrity or privacy. Fortunately,
RPCSEC_GSS has an authentication mode, whereby only the header of
each remote procedure call and response is integrity protected. So,
this minimizes the overhead somewhat, but there is still the cost of
the headers being checksummed. Since IPsec is protecting the
connection, incurring even that minimal per remote procedure call
overhead may not be necessary.
Enter CCM. The server detects that the connection is protected with
IPsec. Via SECINFO, the client is informed that it should use
CCM/Kerberos V5. Via the RPCSEC_GSS protocol, the server
authenticates the end-user on the client with Kerberos V5. The
context tokens exchanged over RPCSEC_GSS are wrapped inside CCM
tokens.
3.2. A Suite of CCM Mechanisms
CCM consists of a suite of GSS mechanisms. GSS can support a concept
call channel bindings, where a GSS mechanism context is bound to a
secure channel (see section 1.1.6 of RFC2743). As noted in RFC2743,
the purpose of channel bindings is to limit the scope within which an
intercepted GSS context token can be used by an attacker. Non-null
channel bindings can be derived from the secure channel's encryption
keys or derived from the network addresses associated with the secure
channel. For environments where it is not feasible to use key-based
channel bindings (e.g., the programming interfaces to get them are
not available) or address-based channel bindings (e.g., the secure
channel may be constructed over a path that requires the use of
Network Address Translation), CCM-NULL is defined. CCM-NULL requires
the use of null channel bindings.
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Non-null channel bindings are highly dependent on the underlying
channel's characteristics. For example with IPsec, the channel
bindings for manual keys, IKEv1, and IKEv2 would be different from
each other. Non-null channel bindings are also underspecified in the
current GSS specifications. Thus this document does not define a
key-based or address-based form for CCM.
As discussed later in this document CCM-MIC exists for the purpose of
optimizing the use of CCM.
Implementations that claim compliance with this document are REQUIRED
to implement CCM-NULL and CCM-MIC. Specifications that make normative
references to CCM are free to mandate any subset of the suite CCM
mechanisms.
CCM-MIC is intended to reduce the instances of full GSS context
establishment to a per- {initiator principal, target} tuple. CCM-MIC
is used to establish a new context by proving that the initiator and
target both have a previously established, unexpired GSS context; the
proof is accomplished by exchanging MICs made with the previously
established GSS context. The CCM-MIC context creation entry points
utilize the CCM_REAL_QOP (discussed in the next section) in the value
to generate and verify the MICs.
3.3. QOPs
The CCM mechanisms provide two QOPs: the default QOP (0) that amounts
to no protection, and a QOP (CCM_REAL_QOP, defined as value 1) that
maps to the default QOP of the underlying GSS mechanism. When
qop_req is 0:
* The MIC token for CCM is always a single octet, of value zero.
* The wrap output token for CCM is equal to the concatenation of
the input token and a single octet (which is equal to zero).
4. Token Formats
This section discusses the protocol visible tokens that GSS consumers
exchange when using CCM.
4.1. Mechanism Object Identifier
There are two classes of Mechanism Object Identifiers (OIDs) for CCM.
The first class consists of the channel binding specific OIDs, and
will be referred to as the CCM-BIND mechanisms. This document defines
one such mechanism:
{ iso(1) identified-organization(3) dod(6) internet(1)
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security(5) mechanisms(5) ccm-family(TBD1) ccm-bind(1) ccm-
null(1) }
The above object identifier is not a complete mechanism OID. A
complete mechanism OID would consist of the above OID as prefix,
followed by a real mechanism OID, such as that of Kerberos V5 as
defined in [RFC1964].
Future extensions to CCM may add non-null channel binding mechanisms
under the ccm-bind(1) node in the OID space.
The second class consists of a single OID for the CCM-MIC mechanism.
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) ccm-family(TBD1) ccm-mic(2) }
The CCM-MIC OID is a complete mechanism OIDs, and is not a prefix.
GSS defines the generic part of a token in ASN.1 encoding. GSS does
not require ASN.1 for the mechanism specific part of a token.
4.2. Tokens for the CCM-BIND mechanisms
4.2.1. Context Establishment Tokens for CCM-BIND Mechanisms
The CCM-BIND context establishment tokens are simple wrappers around
a real GSS mechanism's tokens. The CCM-BIND mechanisms can use one
more context token exchange than the underlying real mechanism. This
is so that that target can be protected from a replay attack in the
event the real mechanism is does not have replay protection. See
[Kasslin] for more information on the attack.
4.2.1.1. Initial Context Token for CCM-BIND
GSS requires that the initial context token from the initiator to the
target use the format as described in section 3.1 of RFC2743. The
format consists of a mechanism independent prefix, and a mechanism
dependent suffix. The mechanism independent token includes the
MechType field. The MechType MUST be equal to the OID of CCM-NULL.
The mechanism dependent portion of the Initial Context Token is
always equal to the full InitialContextToken as returned by the
underlying real mechanism. This will include yet another MechType,
which will have the underlying mechanism's OID.
4.2.1.2. Subsequent Context Tokens for CCM-BIND
A subsequent context token can be any subsequent context token from
the initiator context initialization entry point, or any response
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context from the target's context acceptance entry point. The GSS
specification [RFC2743] does not prescribe any format.
The form of a SubsequentContextToken for a CCM-BIND mechanism, is
always encoded in XDR [RFC1832]. There is a form for the context the
target produces for the initiator, and a form for the context the
initiator produces for the target. These forms are:
enum ccmVerifyState {
CCM_UNVERIFIED = 0,
CCM_VERIFY_FAILED = 1,
CCM_VERIFIED = 2
};
struct ccmBindSubCtxTknTargToInit {
ccmVerifyState ccmBindStatus;
opaque ccmBindRealToken<>;
opaque ccmBindNonce<>;
};
struct ccmBindSubCtxTknInitToTarg {
opaque ccmBindRealToken<>;
opaque ccmBindMic<>;
};
If of non-zero length, the ccmBindRealToken<> field in each of the
above two data types is always that generated by the real mechanism
that CCM-BIND is operating over.
The ccmBindSubCtxTknTargToInit type is the token the target returns
to the initiator. The ccmBindStatus is usually set to CCM_UNVERIFIED,
except as described otherwise. The ccmBindRealToken field is always
equal to the output of the real mechanism's GSS_Accept_sec_context()
entry point. The ccmBindNonce field will always be a zero length
until the real mechanism's GSS_Accept_sec_context() routine returns
GSS_S_COMPLETE. If CCM-BIND knows that the underlying mechanism has
replay protection during context establishment, then it MAY set
ccmBindStatus to CCM_VERIFIED, and set ccmBindNonce to a zero length
value. In this case, CCM-BIND returns GSS_S_COMPLETE to the caller of
its GSS_Accept_sec_context() entry point.
If CCM-BIND does not know if the underlying mechanism has replay
protection, or it knows it does not have replay protection, then
ccmBindStatus MUST be CCM_UNVERIFIED, and ccmBindNonce MUST be a
non-zero length randomly generated string, or a pseudo-random string
generated such that it is unlikely the target will generate a
duplicate in the future. While the underlying real mechanism returned
GSS_S_COMPLETE, CCM-BIND returns GSS_S_CONTINUE_NEEDED to the caller
of its GSS_Accept_sec_context() entry point.
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When the initiator receives a ccmBindSubCtxTknTargToInit token, it
will call the real mechanism's GSS_Init_sec_context() entry point to
process the ccmBindRealToken<> value. If the GSS_Init_sec_context()
entry point of the real mechanism returns GSS_S_CONTINUED needed,
then the CCM-BIND initiator will set the ccmBindMic field to a zero
length string. If GSS_S_COMPLETE was returned, then normally the
ccmBindStatus will be CCM_UNVERIFIED. If so, then the expectation of
the CCM-BIND initiator is that the ccmBindNonce field from the target
MUST be non-zero length. The initiator will set the ccmBindMic field
to the output of GSS_GetMIC() of the ccmBindNonce field, and
GSS_S_CONTINUED will be returned to the caller of CCM-BIND's
GSS_Init_sec_context() entry point. If GSS_GetMIC(), fails, then
the error should be returned to the caller of CCM-BIND's
GSS_Init_sec_context() entry point, and null output token. If the
error from GSS_GetMIC() is not among the set permitted to be returned
from GSS_Init_sec_context(), then the error should be mapped as
follows. GSS_S_CONTEXT_EXPIRED and GSS_S_BAD_QOP should be mapped to
GSS_S_FAILURE.
If the initiator finds that the value the target returned for
ccmBindStatus is CCM_VERIFIED, then the CCM-BIND context is
established, and GSS_S_COMPLETE is returned to the caller of
CCM_BIND's GSS_Init_sec_context() entry point.
When the target receives a ccmBindSubCtxTknInitToTarg with a
ccmBindMic<> value that is non-zero in length, it will call
GSS_VerifyMIC(). The message value will be the ccmBindNonce value the
target generated in the previous context exchange. The per_msg_token
argument will be the ccmBindMic value. The context_handle argument
will be that of the established context of the underlying real
mechanism. If GSS_VerifyMIC() returns GSS_S_COMPLETE, then
ccmBindStatus will be set to CCM_VERIFIED. Otherwise, ccmBindStatus
will be set to CCM_VERIFY_FAILED. The return value of GSS_VerifyMIC()
will be returned to the caller of CCM-BIND's GSS_Accept_sec_context()
entry point, except for those errors are not in the set permitted by
GSS_Accept_sec_context. GSS_S_UNSEQ_TOKEN and GSS_S_GAP_TOKEN should
be mapped to GSS_S_OLD_TOKEN. GSS_S_CONTEXT_EXPIRED should be mapped
to GSS_S_FAILURE.
When the initiator receives a token with ccmBindStatus set to
CCM_VERIFIED, it marks the CCM-BIND context as established, and
returns GSS_S_COMPLETE to the caller of its GSS_Init_sec_context()
entry point. If ccmBindStatus was set to CCM_DENIED, it returns
GSS_S_FAILURE to the caller of its GSS_Init_sec_context() entry
point.
4.2.2. Post Context Establishment Token Formats
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4.2.2.1. MIC Token for CCM-BIND
This token corresponds to the PerMsgToken type as defined in section
3.1 of RFC2743. When the qop_req is the default QOP (0), then the
PerMsgToken is one octet in length with a value of zero. When the
qop_req is CCM_REAL_QOP (1), then PerMsgToken is whatever the
underlying real mechanism returns from GSS_GetMIC() when passed the
default QOP value (0).
4.2.2.2. Wrap Token for CCM-BIND
This token corresponds to the SealedMessage type as defined in
section 3.1 of RFC2743. When the qop_req is the default QOP (0),
then the SealedMessage token is equal to the unmodified input to
GSS_Wrap() concatenated with a single octet with a value of zero.
When the qop_req is CCM_REAL_QOP (1), then SealedMessage is whatever
the underlying real mechanism returns from GSS_Wrap(), when passed
the default QOP value (0).
4.2.3. Other Tokens for CCM-BIND
All other tokens are what the real underlying mechanism returns as a
token.
4.3. Tokens for CCM-MIC
4.3.1. Context Establishment Tokens for CCM-MIC
4.3.1.1. Initial Context Token for CCM-MIC
The initial context token from the initiator to the target uses the
format as described in section 3.1 of RFC2743. The format consists
of a mechanism independent prefix, and a mechanism dependent suffix.
The mechanism independent token includes the MechType field. The
MechType MUST be equal to the OID of CCM-MIC. RFC2743 refers to the
mechanism dependent token as the innerContextToken. This is the
CCM-MIC specific token and is XDR [RFC1832] encoded as follows, using
XDR description language:
struct ccmMicUnWrappedInitToken {
unsigned int ctxMicIndex;
opaque ccmMicCcmBindCtxHandle[20];
opaque ccmMicNonce<>;
};
/*
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* The result of ccmMicUnWrappedInitToken after
* Invoking GSS_GetMIC() on it. qop_req is CCM_REAL_QOP, and
* conf_flag is FALSE.
*/
typedef opaque ccmBindMicWrappedInitToken<>;
Once an initiator has established an initial CCM context with a
target via a CCM-BIND mechanism, the additional contexts can be
established via the CCM-MIC mechanism. The disadvantage of
establishing additional contexts via the CCM-BIND route is that the
underlying mechanism context set up must be repeated, which can be
expensive. Whereas, the CCM-MIC mechanism route merely requires that
the first CCM context's underlying mechanism context be available to
produce an integrity checksum. The initial context token for CCM-MIC
is computed as follows.
* The ccmMicCcmBindCtxHandle is computed as the SHA-1 checksum of
the concatenation of SHA-1 [FIPS] checksums of the context
tokens exchanged by the CCM-BIND mechanism in the order in which
they were processed. For example, the context handle identifier
for a CCM-NULL context exchange over a Kerberos V5 context
exchange would be:
SHA-1( {
SHA-1(CCM-NULL's first initiator token),
SHA-1(CCM-NULL's first initial target token),
SHA-1(CCM-NULL's final initiator token),
SHA-1(CCM-NULL's final target token)
} )
Since the SHA-1 standard mandates a 160 bit output, (20 octets),
ccmMicCcmBindCtxHandle is a fixed length, 20 octet string.
* The field ccmMicNonce is set a random or pseudo random value. It
MUST have length greater than or equal to that of ccmBindNonce
value the target gave the server when the CCM-BIND context was
established It is provided so as to ensure more variability of
the the mic that GSS will calculate when
ccmMicUnWrappedInitToken is GSS_Wrap()ed into
ccmBindMicWrappedInitToken.
* The field ctxMicIndex is the identifier of the CCM-MIC context
relative to the CCM-BIND context (as identified by
ccmMicCcmBindCtxHandle) that the initiator is assigning. The
value for ctxMicIndex is selected by the initiator such that it
is larger than any previous ctxMicIndex for the given
ccmMicCcmBindCtxHandle. This way, the target need only keep
track of the largest ctxMicIndex received. Once ctxMicIndex has
reached the maximum value for an unsigned 32 bit integer, the
given ccmMicCcmBindCtxHandle can no longer be used.
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* Once the above fields are calculated, GSS_Wrap() is performed on
the ccmMicUnWrappedInitToken value, to produce a
ccmBindMicWrappedInitToken value that becomes the initial
context token to send to the target.
4.3.1.2. Subsequent Context Tokens for CCM-MIC
A subsequent context token can be any subsequent context token from
the initiator context initialization entry point, or any response
context from the target's context acceptance entry point. The GSS
specification [RFC2743] does not prescribe any format.
4.3.1.2.1. Subsequent Initiator Context Token for CCM-MIC
As CCM-MIC has only one round trip for context token exchange, there
are no subsequent initiator context tokens.
4.3.1.2.2. Response Token for CCM-MIC
The CCM response token, in XDR encoding is:
enum ccmMicStatus {
CCM_OK = 0,
/*
* ccmMicCcmBindCtxHandle was malformed.
*/
CCM_ERR_HANDLE_MALFORMED = 1,
/*
* The GSS context corresponding to
* ccmMicCcmBindCtxHandle has expired.
*/
CCM_ERR_HANDLE_EXPIRED = 2,
/*
* ccmMicCcmBindCtxHandle was not found.
*/
CCM_ERR_HANDLE_NOT_FOUND = 3,
/*
* The ctxMicIndex has already been received
* by the target. Or the maximum ctxMicIndex has
* been previously received.
*/
CCM_ERR_TKN_REPLAY = 4,
/*
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* Channel binding type mismatch between CCM-BIND context
* and the CCM-MIC initial context.
*/
CCM_ERR_CHAN_MISMATCH = 5,
/*
* The GSS_Unwrap() failed on initial context token
*/
CCM_ERR_TKN_UNWRAP = 6,
/*
* The GSS_GetMIC() called failed on the target().
*/
CCM_ERR_TKN_GET_MIC = 7,
/*
* The GSS_Wrap() failed on the initiator. Not reported
* by target.
*/
CCM_ERR_TKN_WRAP = 8,
/*
* The GSS_VerifyMIC() failed on the initiator. Not
* reported by target.
*/
CCM_ERR_TKN_VER_MIC = 9
};
/*
* GSS errors returned by the underlying mechanism
*/
struct ccmMicRealGssErr {
unsigned int ccmMicGssMajor;
unsigned int ccmMicGssMinor;
};
/*
* The response context token for CCM-MIC.
*/
union ccmMicResp switch (ccmMicStatus status) {
case CCM_OK:
opaque ccmMicRespInitTkn<>;
case CCM_ERR_TKN_UNWRAP:
case CCM_ERR_TKN_GET_MIC:
ccmMicRealGssErr ccmMicGssErr;
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default:
void;
};
If a value of the status field is CCM_OK, then the CCM-MIC context
has been established on the target. The field ccmMicRespInitTkn is
equal to the output of GSS_GetMIC() (qop_req is CCM_REAL_QOP (1)) on
the entire and first token that came from the initiator. In other
words, the first input_token value to GSS_Accept_sec_context(). This
is necessary because the inner token from the initiator is wrapped
with GSS_Wrap(), and thus contains a MIC. If we performed
GSS_GetMIC() on the unwrapped inner token, then for some underlying
mechanisms, we would end up with a ccmMicRespInitTkn in the response
token equal to what was embedded in the request token.
If the status field is CCM_ERR_TKN_UNWRAP or CCM_ERR_TKN_GET_MIC,
then ccmMicGssErr.ccmMicGssMajor and ccmMicGssErr.ccmMicGssMinor are
set to the major and minor GSS statuses as returned by GSS_Unwrap()
or GSS_GetMIC(). The values for the ccmMicGssMajor field are as
defined in [RFC2744]. The values for the ccmMicGssMinor field are
both mechanism dependent and mechanism implementation dependent.
They are nonetheless potentially useful as debugging aids.
4.3.2. MIC Token for CCM-MIC
The MIC token for CCM-MIC is the same as the MIC token for CCM-BIND.
4.3.3. Wrap Token for CCM-MIC
The wrap token for CCM-MIC is the same as the wrap token for CCM-
BIND.
4.3.4. Context Deletion Token
The context deletion token for CCM-MIC is a zero length token.
4.3.5. Exported Context Token
The Exported context token for CCM-MIC is implementation defined.
4.3.6. Other Tokens for CCM-MIC
All other tokens are the same as corresponding tokens for CCM-BIND.
5. Implementation Issues
The "over the wire" aspects of CCM have been completely specified.
However, GSS is usually implemented as an Application Programming
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Interface (the GSS-API), and security mechanisms are often
implemented as modules that are plugged into the GSS-API. It is
useful to discuss implementation issues and workable resolutions.
The reader is cautioned that the authors have not implemented CCM, so
what follows is at best a series of educated guesses.
5.1. Management of ccmMicCcmBindCtxHandle
The ccmMicCcmBindCtxHandle value is computed by the initiator and
target based on SHA-1 computations of the CCM-BIND context tokens.
There is a space/time trade off between the initiator and target
storing the sequence of context tokens until needed by CCM-BIND,
versus computing the SHA-1 checksums and then disposing of the
context tokens when CCM-BIND no longer needs them. If it is likely
there will be CCM-MIC contexts created for the CCM-BIND context, and
if the sequence of context tokens requires more space than a 20 octet
SHA-1 value, then the tradeoff is obvious.
Since the bit space of all possible sequences of CCM-BIND context
tokens is larger than the 160 bit space of possible SHA-1 checksums,
in theory two or more different CCM-BIND contexts will produce
produce the same SHA-1 context, and thus for CCM-MIC context
initiation, there will be ambiguity as to which CCM-BIND context the
initiator is binding to. The target can resolve this ambiguity by
attempting to unwrap the inner context token from the CCM-MIC
initiator for each matching CCM-BIND context. In theory no more than
one GSS_Unwrap() attempt for each matching CCM-BIND context will
succeed. If multiple succeed, then clearly the underlying mechanism
is doing poor job at generating "unique" session keys. CCM
implementations that detect this SHOULD log it so that the problem in
the underlying mechanism can be discovered and fixed.
5.2. CCM-BIND Versus CCM-MIC
The first time a CCM context is needed between an principal on the
initiator and a principal on the target, the initiator has no choice
but to create an underlying mechanism context via a CCM-BIND context
token exchange. Once that is done, subsequent CCM contexts between
the initiator and target can be created via CCM-MIC. CCM-MIC context
establishment is better because no more than one round trip is
necessary to establish a CCM context, and because the overhead of the
establishing a real, underlying mechanism context is avoided.
5.3. Initiating CCM-MIC Contexts
The issue is how to associate an CCM-BIND established security
context with a new CCM-MIC context, There are no existing interfaces
defined in the GSS-API for associating one GSS context with another.
This then is the key issue for implementations of CCM-MIC.
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We will assume that GSS-API implementation is in the C programming
language and therefore the GSS-API C bindings [RFC2744] are being
used. The CCM mechanism implementation will have a table that maps
ccmMicCcmBindCtxHandle values to gss_ctx_id_t values (see section
5.19 of [RFC2744]). The latter are GSS-API context handles as
returned by gss_init_sec_context(). In addition, each CCM context has
a reference to its underlying mechanism context.
Let us suppose the application decides it will use CCM-MIC. CCM-MIC
has a well known mechanism OID which the application can check for.
The point where the initiator calls GSS_Init_sec_context(), is a
logical place to associate an existing CCM-BIND context with a new
CCM-MIC context. Here is where special CCM handling is necessary in
order to associate a security context with a CCM context. We discuss
several approaches.
1. The first approach is for the CCM-MIC's GSS_Init_sec_context()
entry point to pass as the claimant_cred_handle the
output_context_handle as returned by GSS_Init_sec_context() for
a previously established CCM-BIND context. Such an approach may
work well with applications that normally pass
GSS_C_NO_CREDENTIAL as the claimant_cred_handle.
2. The second approach derives from the observation that normally,
the first time GSS_Init_sec_context() is called, the input_token
field is NULL and the initial context_handle (type gss_ctx_id_t)
is also NULL. The input_token is supposed to be the token
received from the target's context acceptance routine, which has
the XDR type ccmMicResp. Overloading the input_token is one
way. By passing in a non-null input_token, and a NULL pointer
to the context_handle (using the C bindings calling conventions
for gss_init_sec_context()), this will tell the CCM-MIC
initiator that input_token containing information to to
associate a new CCM-MIC context with an existing CCM-BIND
context. In the C programming language, we could thus have have
input_token containing:
typedef struct {
gss_ctx_id_t ccmMicCcmBindCtxPtr;
} ccmMicCcmBindBootStrap;
The CCM entry point for creating contexts on the initiator side
would, if being called for the first time (*context_handle is
NULL), interpret the presence of the input token with an invalid
status as the ccmMicCcmBindBootStrap. It would use
ccmMicCcmBindCtxPtr to lookup the corresponding
ccmMicCcmBindCtxHandle in the aforementioned gss_ctx_id_t to
ccmMicCcmBindCtxHandle mapping table. It would then proceed to
generate an output token encoded as XDR type CCM_MIC_init_t,
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described in the section entitled "Initial Context Token for
CCM-MIC".
Regardless of the approach taken, the first time GSS_Init_sec_context
is called, assuming success, it will return GSS_S_CONTINUE_NEEDED,
because it will need to process the token returned by the target.
The second time it is called, assuming success, it will return
GSS_S_COMPLETE.
5.4. Accepting CCM-MIC Contexts
The CCM-MIC target receives an opaque ccmMicCcmBindCtxHandle value as
part of the mechanism dependent part of the initial context token.
Originally, this opaque handle came from the target as a result of
previously creating a context via a CCM-BIND context exchange. If
the opaque handle is still valid, then the target can easily
determine the original CCM-BIND context, and from that, the CCM-BIND
mechanism's context. With the underlying context, GSS_VerifyMIC()
can be invoked (with a qop_req of CCM_REAL_QOP (1)) to verify the
mic_nonce of the input token, and GSS_GetMIC() can be used to
generate the ccmMicRespInitTkn field of the output token. By
comparing the ctxMicIndex in the initiator's token with highest value
recorded by the target, the target takes care to ensure that
initiator has not replayed an initial CCM-MIC context token.
5.5. Non-Token Generating GSS-API Routines
Since the CCM module will record the underlying mechanism's context
pointer in its internal data structures, this provides a simple
answer to what to do when GSS-API is invoked on a CCM context that
does not generate any tokens for the GSS peer. When CCM is called
for such an operation, it simply re-invokes the GSS-API call, but on
the recorded underlying context.
5.6. CCM-MIC and GSS_Delete_sec_context()
The CCM-MIC entry point for GSS_Delete_sec_context() should not call
the underlying mechanism's GSS_Delete_sec_context() routine. If it
did, this would effectively delete all CCM-MIC context's associating
with the same underlying mechanism.
5.7. GSS Status Codes
5.7.1. Status Codes for CCM-BIND
CCM-BIND mechanisms define no minor status codes. If the underlying
mechanism is not available, then a CCM-BIND mechanism will return
GSS_S_BAD_MECH and minor status of zero. Otherwise, it will return
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whatever major and minor status codes the underlying mechanism
returns.
5.7.2. Status Codes for CCM-MIC
Generally, major and minor status codes for will be whatever major
and minor status codes the underlying CCM-BIND mechanism returns.
However, for GSS_Init_sec_context() and GSS_Accept_sec_context(),
this is not the case because the those operations are invoking
routines (GSS_Wrap() and GSS_Unwrap()) that have major statuses that
are not subsets of the legal status returns from
GSS_Init_sec_context() and GSS_Accept_sec_context(). Moreover, in
some cases for GSS_Init_sec_context(), the minor and major status are
driven from the target, and the target's codes will not always be
among the legal set for GSS_Init_sec_context().
5.7.2.1. CCM-MIC: GSS_Accept_sec_context() status codes
The minor status code for GSS_Accept_sec_context is always from the
set defined in the ccmMicStatus type. If GSS_Unwrap() reports a
major status failure, then the minor status will be
CCM_ERR_TKN_UNWRAP, and the reported major status will what
GSS_Unwrap() reports, with exceptions as according to the following
table:
major status code from GSS_Unwrap major status code reported
by GSS_Accept_sec_context
to caller.
-----------------------------------------------------------------
GSS_S_BAD_SIG GSS_S_BAD_SIG
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN
GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN
If GSS_GetMIC() reports a major status failure, then the minor status
will be CCM_ERR_TKN_GET_MIC, and the reported major status will be
what GSS_GetMIC() reports, with exceptions as according to the
following table:
major status code from GSS_GetMIC major status code reported
by GSS_Accept_sec_context()
to caller.
------------------------------------------------------------------
GSS_S_BAD_QOP GSS_S_FAILURE
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
The target will always report the actual GSS major and minor codes to
the initiator. The initiator will map the GSS major code as
described in the next subsection.
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5.7.2.2. CCM-MIC: GSS_Init_sec_context() status codes
The minor status code for GSS_Init_sec_context is always from the set
defined in the ccmMicStatus type.
If the minor status code came from the target, then that will always
be what GSS_Init_sec_context() reports. The most of the minor codes
from the target are to be mapped to the major status code as follows:
minor status code major status code
from target reported to caller of
GSS_Init_sec_context()
----------------------------------------------------
CCM_OK GSS_S_COMPLETE
CCM_ERR_HANDLE_MALFORMED GSS_S_DEFECTIVE_TOKEN
CCM_ERR_HANDLE_EXPIRED GSS_S_CREDENTIALS_EXPIRED
CCM_ERR_HANDLE_NOT_FOUND GSS_S_CREDENTIALS_EXPIRED
CCM_ERR_TKN_REPLAY GSS_S_DUPLICATE_TOKEN
CCM_ERR_CHAN_MISMATCH GSS_S_BAD_BINDINGS
CCM_ERR_TKN_WRAP GSS_S_FAILURE
CCM_ERR_TKN_VER_MIC GSS_S_FAILURE
Note that in the above table CCM_ERR_TKN_WRAP and CCM_ERR_TKN_VER_MIC
MUST not be returned by the target. But if they are, then the
initiator reports GSS_S_FAILURE.
If the minor status code from the target is CCM_ERR_TKN_UNWRAP or
CCM_ERR_TKN_GET_MIC, then the target will also report the major
status code it got from GSS_Unwrap() or GSS_GetMIC(). The major
status from the target will be be reported by GSS_Init_sec_context()
to its caller with exceptions as according to the following table:
major status code from target major status code reported
by GSS_Init_sec_context()
to caller
-----------------------------------------------------------------
GSS_S_BAD_QOP GSS_S_FAILURE
GSS_S_BAD_SIG GSS_S_BAD_SIG
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN
GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN
If GSS_Wrap() fails on the initiator, then the minor status will be
CCM_ERR_TKN_WRAP, and the major status will what GSS_Wrap() reports,
with exceptions as according to the following table:
major status code from GSS_Wrap major status code reported
by GSS_Init_sec_context()
to caller
---------------------------------------------------------------
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
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or
GSS_S_DEFECTIVE_CREDENTIAL
GSS_S_BAD_QOP GSS_S_FAILURE
If GSS_VerifyMIC() fails on the initiator, then the minor status will
be CCM_ERR_TKN_VER_MIC, and the major status will what
GSS_VerifyMIC() reports, with exceptions as according to the
following table:
major status code from GSS_VerifyMIC major status code reported
by GSS_Init_sec_context()
to caller
---------------------------------------------------------------
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN
GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN
6. Advice for NFSv4 Implementors
The NFSv4.0 specification does not mandate CCM, so client and server
implementations should not insist on its use. When a server wants a
client to try to use CCM, it can return a NFS4ERR_WRONGSEC error to
the client. The client will then follow up with a SECINFO request.
The response to the SECINFO request should list first the CCM-BIND
mechanisms it supports, second the CCM-MIC mechanism (if supported),
and finally, the conventional security flavors the server will accept
for access to file object. If the client supports CCM, it will use
it. Otherwise, it will have to stick with a conventional flavor.
Since the CCM-MIC OID is general, rather than a separate CCM-MIC OID
for every real mechanism, the NFS server will have be careful to make
sure that a CCM-MIC context is authorized access an object. For
example suppose /export is exported such that SPKM-3 is the
authorized underlying mechanism, and CCM-NULL + SPKM-3 and CCM-MIC
are similarly authorized to access /export. Suppose CCM-NULL is
created over a Kerberos V5 context, and then CCM-MIC is used to
derived a context from the CCM-NULL context. If the NFS server
simply records that the OID of CCM-MIC is authorized to access
/export, then Kerberos V5 authenticated users will be mistakenly
allowed access. Instead, the server needs to examine what context
the CCM-MIC context is associated with, and check that context's OID
against the authorized list of OIDs for /export.
7. Security Considerations
There are many considerations for the use CCM, since it is reducing
security at one protocol layer in trade for equivalent security at
another layer. In this discussion, we will assume that cryptography
is being used in the application and lower protocol layers.
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* CCM should not be used whenever the combined key
strength/algorithm strength of the lower protocol layer securing
the connection is weaker than what the underlying GSS context
can provide.
* CCM should not be used if the lower level protocol does not
offer comparable or superior security services to that the
application would achieve with GSS. For example, if the lower
level protocol offers integrity, but the application wants
privacy, then CCM is inappropriate.
* The use of CCM contexts over secured connections can be
characterized nearly secure instead of as secure as using the
underlying GSS context for protecting each application message
procedure call. The reason is that applications can multiplex
the traffic of multiple principals over a single connection and
so the ciphertext in the traffic is encrypted with multiple
session keys. Whereas, a secure connection method such as IPsec
is protected with per host session keys. Therefore, an attacker
has more cipher text per session key to perform cryptanalysis
via connections protected with IPsec, versus connections
protected with GSS.
* Related to the previous bullet, the management of private keys
for a secure channel is often outside the control of the user of
CCM. If the secure channel's private keys are compromised, then
all users of the secure channel are compromised.
* CCM contexts created during one session or transport connection
SHOULD not be used for subsequent sessions or transport
connections. In other words, full initiator to target
authentication SHOULD occur each time a session or transport
connection is established. Otherwise, there is nothing
preventing an attacker from using a CCM context from one
authenticated session or connection to trivially establish
another, unauthenticated session or connection. For efficiency,
a CCM-BIND context from a previous session or connection MAY be
used to establish a CCM-MIC context.
If the application protocol using CCM has no concept of a
session and does not use a connection oriented transport, then
there is no sequence of state transitions that tie the CCM
context creation steps with the subsequent message traffic of
the application protocol. Thus it can be hard to assert that
the subsequent message traffic is truly originated by the CCM
initiator's principal. For this reason, CCM SHOULD NOT be used
with applications that do not have sessions or do not use
connection oriented transports.
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* The underlying secure channel SHOULD be end to end, from
initiator to the target. It is permissible for the user to
configure the underlying secure channel to not be end to end,
but this should only be done if user has confidence in the
intermediate end points. For example, suppose the application
is being used behind a firewall that performs network address
translation. It is possible to have an IPsec secure channel
from the initiator to the firewall, and a second secure channel
from the firewall to the target, but not from the initiator to
the target. So, if the firewall is compromised by an attacker
in the middle, the use of CCM to avoid per message
authentication is useless. Of course, if the initiator's node
created a IP-layer tunnel between it and the target, end to end
channel security would be achieved.
* It has been stated that it is not uncommon to find IPsec
deployments where multiple nodes share common private keys
[Black]. The use of CCM is discouraged in such environments,
since the compromise of one node compromises all the other nodes
sharing the same private key.
* Applications using CCM MUST ensure that the binding between the
CCM context and the secure channel is legitimate for each
message that references the CCM context. In other words, the
referenced CCM context in a message MUST be established in the
same secure channel as the message.
* When the same secure channel is multiplexing traffic for
multiple users, the initiator has to ensure the CCM context is
only accessible to the initiator principal that has established
it in the first place. One possible way to ensure that is by
placing CCM contexts in the privileged address space offering
only controlled indexed access.
* CCM does not unnecessarily inflate the scope of the trust
domain, as does for example AUTH_SYS [RFC1831] over IPSec. By
requiring the authentication in the CCM context initialization
(using a previously established context), the trust domain does
not extend to the client.
* Both the traditional mechanisms and CCM rely on the security of
the client to protect locally logged on users. Compromise of
the client impacts all users on the same client. CCM does not
make the problem worse.
* The CCM context MUST be established over the same secure channel
that the subsequent message traffic will be using. This way,
the binding between the initial authentication and the
subsequent traffic is ensured.
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* If an application is using IPsec and CCM-NULL then then the site
where the application is deployed should configure the IPsec SPD
to carefully limit the ports and nodes that are allowed create
security associations to application targets.
* CCM contexts should not be used forever without re-
authenticating periodically via the underlying mechanism. One
rational approach is for the CCM context to persist no longer
than the underlying mechanism context. Implementing this via
the GSS-API is simple. Applications can periodically invoke
gss_context_time() to find out how long the context will be
valid. Moreover, CCM can enforce this by invoking
gss_context_time() and the system time of day API to get an
expiration date when the CCM mechanism is established. Each
subsequent call can check the time of day against the
expiration, and if expired, return GSS_S_CONTEXT_EXPIRED.
8. CCM XDR Description
Here is the XDR description for CCM-BIND and CCM-MIC:
enum ccmVerifyState {
CCM_UNVERIFIED = 0,
CCM_VERIFY_FAILED = 1,
CCM_VERIFIED = 2
};
struct ccmBindSubCtxTknTargToInit {
ccmVerifyState ccmBindStatus;
opaque ccmBindRealToken<>;
opaque ccmBindNonce<>;
};
struct ccmBindSubCtxTknInitToTarg {
opaque ccmBindRealToken<>;
opaque ccmBindMic<>;
};
enum ccmMicStatus {
CCM_OK = 0,
/*
* ccmMicCcmBindCtxHandle was malformed.
*/
CCM_ERR_HANDLE_MALFORMED = 1,
/*
* The GSS context corresponding to
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* ccmMicCcmBindCtxHandle has expired.
*/
CCM_ERR_HANDLE_EXPIRED = 2,
/*
* ccmMicCcmBindCtxHandle was not found.
*/
CCM_ERR_HANDLE_NOT_FOUND = 3,
/*
* The ctxMicIndex has already been received
* by the target. Or the maximum ctxMicIndex has
* been previously received.
*/
CCM_ERR_TKN_REPLAY = 4,
/*
* Channel binding type mismatch between CCM-BIND context
* and the CCM-MIC initial context.
*/
CCM_ERR_CHAN_MISMATCH = 5,
/*
* The GSS_Unwrap() failed on initial context token
*/
CCM_ERR_TKN_UNWRAP = 6,
/*
* The GSS_GetMIC() called failed on the target().
*/
CCM_ERR_TKN_GET_MIC = 7,
/*
* The GSS_Wrap() failed on the initiator. Not reported
* by target.
*/
CCM_ERR_TKN_WRAP = 8,
/*
* The GSS_VerifyMIC() failed on the initiator. Not
* reported by target.
*/
CCM_ERR_TKN_VER_MIC = 9
};
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/*
* GSS errors returned by the underlying mechanism
*/
struct ccmMicRealGssErr {
unsigned int ccmMicGssMajor;
unsigned int ccmMicGssMinor;
};
/*
* The response context token for CCM-MIC.
*/
union ccmMicResp switch (ccmMicStatus status) {
case CCM_OK:
opaque ccmMicRespInitTkn<>;
case CCM_ERR_TKN_UNWRAP:
case CCM_ERR_TKN_GET_MIC:
ccmMicRealGssErr ccmMicGssErr;
default:
void;
};
9. IANA Considerations
XXX Note 1 to IANA: The CCM-BIND mechanism OID prefixes and the CCM-
MIC mechanism OID must be assigned and registered by IANA. Please
look for TBD1 in this document and notify the RFC Editor what value
you have assigned.
XXX Note 1 to RFC Editor: When IANA has made the OID assignments,
please do the following:
* Delete the "XXX Note 1 to RFC Editor: ..." paragraph.
* Replace occurrences of TBD1 with the value assigned by IANA.
* Replace the "XXX Note 1 to IANA: ..." paragraph with:
OIDs for the CCM-BIND mechanism prefix, and for the CCM-MIC
mechanism have been assigned by, and registered with IANA,
with this document as the reference.
XXX Note 2 to IANA: Please assign RPC flavor numbers for values
currently place held in this document as TBD2 through TBD5. Also
please establish the registry that RFC2623 mandates.
XXX Note 2 to RFC Editor: When IANA has made the RPC flavor number
assignments, please do the following:
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* Delete the "XXX Note 2 to RFC Editor: ..." paragraph.
* Replace occurrences of TBD2 through and including TBD5 withe
flavor number assignments from IANA.
Section 6, "IANA Considerations" of [RFC2623] established a registry
for mapping GSS mechanism OIDs to RPC pseudo flavor numbers. This
registry was augmented in the NFSv4 specification [RFC3530] with
several more entries. This document adds the following entries to
the registry:
1 == number of pseudo flavor
2 == name of pseudo flavor
3 == mechanism's OID
4 == quality of protection
5 == RPCSEC_GSS service
1 2 3 4 5
--------------------------------------------------------------
TBD2 ccm-mic 1.3.6.1.5.5.TBD1.2 0 rpc_gss_svc_none
TBD3 ccm-null-krb5 1.3.6.1.5.5.TBD1.1.1. 0 rpc_gss_svc_none
1.2.840.113554.1.2.2
TBD4 ccm-null-spkm3 1.3.6.1.5.5.TBD1.1.1. 0 rpc_gss_svc_none
1.3.6.1.5.5.1.3
TBD5 ccm-null-lipkey 1.3.6.1.5.5.TBD1.1.1. 0 rpc_gss_svc_none
1.3.6.1.5.5.1.3
10. Acknowledgements
Dave Noveck, for the observation that NFS version 4 servers could
downgrade from integrity service to plain authentication service if
IPsec was enabled. David Black, Peng Dai, Sam Hartman, Martin Rex,
and Julian Satran, for their critical comments. Much of the text for
the "Security Considerations" section comes directly from David and
Peng.
11. Normative References
[RFC1832]
R. Srinivasan, RFC1832, "XDR: External Data Representation
Standard", August, 1995.
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[RFC2025]
C. Adams, RFC2025: "The Simple Public-Key GSS-API Mechanism
(SPKM)," October 1996, Status: Standards Track.
[RFC2119]
S. Bradner, RFC2119, "Key words for use in RFCs to Indicate
Requirement Levels," March 1997.
[RFC2401]
S. Kent, R. Atkinson, RFC2401, "Security Architecture for the
Internet Protocol ", November, 1998.
[RFC2409]
D. Harkins and D. Carrel, RFC2119: "The Internet Key Exchange
(IKE)," November 1998.
[RFC2743]
J. Linn, RFC2743, "Generic Security Service Application Program
Interface Version 2, Update 1", January, 2000.
[RFC2744]
J. Wray, RFC2744, "Generic Security Service API Version 2 : C-
bindings", January, 2000.
[RFC2847]
M. Eisler, RFC2847: "LIPKEY - A Low Infrastructure Public Key
Mechanism Using SPKM," June 2000, Status: Standards Track.
[FIPS]U.S. Department of Commerce / National Institute of Standards
and Technology, FIPS PUB 180-1, "Secure Hash Standard", May 11,
1993.
12. Informative References
[RFC1831]
R. Srinivasan, RFC1831, "RPC: Remote Procedure Call Protocol
Specification Version 2", August, 1995.
[RFC1964]
J. Linn, RFC1964, "The Kerberos Version 5 GSS-API Mechanism",
June 1996.
[RFC2203]
M. Eisler, A. Chiu, L. Ling, RFC2203, "RPCSEC_GSS Protocol
Specification", September, 1997.
[RFC2623]
M. Eisler, RFC2623, "NFS Version 2 and Version 3 Security Issues
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INTERNET-DRAFT CCM July 2004
and the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5", June
1999.
[RFC3530]
S. Shepler, B. Callaghan, D. Robinson, R. Thurlow, C. Beame, M.
Eisler, D. Noveck, RFC3530, "Network File System (NFS) version 4
Protocol", April 2003.
[Black]
D. Black, EMail message on the NFSv4 working group alias,
February 28, 2003.
[DAFS]
Mark Wittle (Editor), "DAFS Direct Access File System Protocol,
Version: 1.00", September 1, 2001.
[Kasslin]
Kasslin, K. "Attacks on Kerberos V in a Windows 2000
Environment", 2003.
http://www.hut.fi/~autikkan/hakkeri/docs/phase1/pdf/
LATEST_final_report.pdf
13. Authors' Addresses
Mike Eisler
5765 Chase Point Circle
Colorado Springs, CO 80919
USA
Phone: 719-599-9026
EMail: mike@eisler.com
Nicolas Williams
Sun Microsystems, Inc.
5300 Riata Trace CT
Austin, TX 78727
USA
EMail: nicolas.williams@sun.com
14. IPR Notices
The IETF takes no position regarding the validity or scope of any
intellectual property 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; neither does it represent that it
has made any effort to identify any such rights. Information on the
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IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
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The IETF invites any interested party to bring to its attention any
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15. Copyright Notice
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Expires: January 2005 [Page 28]
