Network Working Group M. Eisler
Internet-Draft Network Appliance, Inc.
N. Williams
Sun Microsystems, Inc.
May 2003
The Channel Conjunction Mechanism (CCM) for GSS
draft-ietf-nfsv4-ccm-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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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.
TABLE OF CONTENTS
1. Conventions Used in this Document . . . . . . . . . . . . . . . 3
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2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Example Application of CCM . . . . . . . . . . . . . . . . . 4
3.2. A Suite of CCM Mechanisms . . . . . . . . . . . . . . . . . . 4
3.3. QOPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Token Formats . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Mechanism Object Identifier . . . . . . . . . . . . . . . . . 6
4.2. Tokens for the CCM-BIND mechanisms . . . . . . . . . . . . . 6
4.3. Context Establishment Tokens for CCM-BIND Mechanisms . . . . 6
4.3.1. Initial Context Token for CCM-BIND . . . . . . . . . . . . 7
4.3.2. Subsequent Context Tokens for CCM-BIND . . . . . . . . . . 7
4.3.2.1. Subsequent Initiator Context Initialization Token for
CCM-BIND . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3.2.2. Response Token for CCM-BIND . . . . . . . . . . . . . . . 7
4.4. MIC Token for CCM-BIND . . . . . . . . . . . . . . . . . . . 7
4.5. Wrap Token for CCM-BIND . . . . . . . . . . . . . . . . . . . 7
4.6. Other Tokens for CCM-BIND . . . . . . . . . . . . . . . . . . 8
4.7. Tokens for CCM-MIC . . . . . . . . . . . . . . . . . . . . . 8
4.8. Context Establishment Tokens for CCM-MIC . . . . . . . . . . 8
4.8.1. Initial Context Token for CCM-MIC . . . . . . . . . . . . . 8
4.8.2. Subsequent Context Tokens for CCM-MIC . . . . . . . . . . . 9
4.8.2.1. Subsequent Initiator Context Initialization Token for
CCM-MIC . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.8.2.2. Response Token for CCM-MIC . . . . . . . . . . . . . . 10
4.9. MIC Token for CCM-MIC . . . . . . . . . . . . . . . . . . . 12
4.10. Wrap Token for CCM-MIC . . . . . . . . . . . . . . . . . . 12
4.11. Context Deletion Token . . . . . . . . . . . . . . . . . . 12
4.12. Exported Context Token . . . . . . . . . . . . . . . . . . 12
4.13. Other Tokens for CCM-MIC . . . . . . . . . . . . . . . . . 12
5. GSS Channel Bindings for Common Secure Channel Protocols . . 12
5.1. GSS Channel Bindings for IKEv1 . . . . . . . . . . . . . . 13
5.2. GSS Channel Bindings for IKEv2 . . . . . . . . . . . . . . 13
5.3. GSS Channel Bindings for SSHv2 . . . . . . . . . . . . . . 13
5.4. GSS Channel Bindings for TLS . . . . . . . . . . . . . . . 13
6. Use of Channel Bindings with CCM-BIND and SPKM . . . . . . . 13
7. CCM-KEY and Anonymous IPsec . . . . . . . . . . . . . . . . . 14
8. Other Protocol Issues for CCM . . . . . . . . . . . . . . . . 14
9. Implementation Issues . . . . . . . . . . . . . . . . . . . . 15
9.1. Management of gss_targ_ctx . . . . . . . . . . . . . . . . 15
9.2. CCM-BIND Versus CCM-MIC . . . . . . . . . . . . . . . . . . 15
9.3. Initiating CCM-MIC Contexts . . . . . . . . . . . . . . . . 16
9.4. Accepting CCM-MIC Contexts . . . . . . . . . . . . . . . . 17
9.5. Non-Token Generating GSS-API Routines . . . . . . . . . . . 17
9.6. CCM-MIC and GSS_Delete_sec_context() . . . . . . . . . . . 17
9.7. GSS Status Codes . . . . . . . . . . . . . . . . . . . . . 18
9.7.1. Status Codes for CCM-BIND . . . . . . . . . . . . . . . . 18
9.7.2. Status Codes for CCM-MIC . . . . . . . . . . . . . . . . 18
9.7.2.1. CCM-MIC: GSS_Accept_sec_context() status codes . . . . 18
9.7.2.2. CCM-MIC: GSS_Init_sec_context() status codes . . . . . 19
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9.8. Channel Bindings on the Target . . . . . . . . . . . . . . 20
10. Advice for NFSv4 Implementors . . . . . . . . . . . . . . . 21
11. Man in the Middle Attacks without CCM-KEY . . . . . . . . . 21
12. Security Considerations . . . . . . . . . . . . . . . . . . 22
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . 25
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
15. Normative References . . . . . . . . . . . . . . . . . . . . 27
16. Informative References . . . . . . . . . . . . . . . . . . . 28
17. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 28
18. IPR Notices . . . . . . . . . . . . . . . . . . . . . . . . 29
19. Copyright Notice . . . . . . . . . . . . . . . . . . . . . . 29
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
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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
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. CCM-NULL, CCM-ADDR, and
CCM-KEY bind a GSS mechanism context to a secure channel via GSS
channel bindings (see section 1.1.6 of RFC2743). As noted in
RFC2743, the purpose of channel bindings are to limit the scope
within which an intercepted GSS context token can be used by an
attacker. CCM-KEY requires the use of channel bindings that are
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derived from the secure channel's encryption keys. CCM-ADDR requires
the use of channel bindings that are derived from 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
also defined. CCM-NULL requires the use of null channel bindings.
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-KEY and CCM-MIC. CCM-NULL and CCM-ADDR
implementation are OPTIONAL. Specifications that make normative
references to CCM are free to mandate any subset of the suite CCM
mechanisms.
Because the GSS channel bindings to IPsec [RFC2401, RFC2409, IKEv2]
have not been previously defined, and to ensure the usefulness of
CCM, they are defined in this document.
Also, the SPKM (1, 2 and 3) [RFC2025, RFC2847] mechanism is not clear
on how channel bindings work with SPKM; a simple clarification is
provided.
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 later Overview section) in the
value to generate and verify the MICs. The type of channel bindings
used when initiating CCM-MIC contexts MUST match that used when
creating the previously established context.
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. The MIC
tokens for CCM are zero length values. When qop_req is 0, the wrap
output tokens for CCM are equal to the input tokens.
[ XXX - We assume that applications can cope with zero length
MICs. We propose that implementations try and find out. We may
revisit this by requiring a small (8-32 bits) MIC token.
However, given that the C bindings of GSS allocates the MIC on
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the heap, this could introduce an unnecessary and expensive
allocation, we suggest applications be fixed to deal with zero
length tokens. ]
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:
{iso(1)identified-organization(3)dod(6)internet(1)security(5)
mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-null(1)}
{iso(1)identified-organization(3)dod(6)internet(1)security(5)
mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-addr(2)}
{iso(1)identified-organization(3)dod(6)internet(1)security(5)
mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-key(3)}
The above three object identifiers are not complete mechanism OIDs.
Complete CCM mechanism OIDs MUST consist of one of the above OIDs as
prefix, followed by a real mechanism OID, such as that of Kerberos V5
as defined in [RFC1964]. 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
4.3. 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 use the same
number context token exchanges as required by they underlying real
mechanism.
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4.3.1. 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,
CCM-ADDR, or CCM-KEY. 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.
4.3.2. 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
context from the target's context acceptance entry point. The GSS
specification [RFC2743] does not prescribe any format.
4.3.2.1. Subsequent Initiator Context Initialization Token for CCM-BIND
A SubsequentContextToken for a CCM-BIND mechanism is equal to that
returned by the initiator's context initialization routine of the
underlying real mechanism.
4.3.2.2. Response Token for CCM-BIND
The response token for a CCM-BIND mechanism is equal to that returned
by the target's context acceptance routine of the underlying real
mechanism.
4.4. 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 a quantity zero bits in length. A programming API
that calls GSS_GetMIC() with the default QOP will thus produce an
octet string of zero length.
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).
4.5. 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().
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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).
4.6. Other Tokens for CCM-BIND
All other tokens are what the real underlying mechanism returns as a
token.
4.7. Tokens for CCM-MIC
4.8. Context Establishment Tokens for CCM-MIC
4.8.1. 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:
typedef struct {
unsigned int ctx_sh_number;
unsigned int rand;
} CCM_nonce_t;
typedef struct {
CCM_nonce_t nonce;
opaque gss_targ_ctx[20];
opaque chan_bindings<>;
} CCM_MIC_unwrapped_init_token_t;
/*
* The result of CCM_MIC_unwrapped_init_token_t after
* Invoking GSS_GetMIC() on it. qop_req is CCM_REAL_QOP, and
* conf_flag is FALSE.
*/
typedef opaque CCM_MIC_wrapped_init_token_t<>;
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 re-
establishing additional contexts via the CCM-BIND route is that the
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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 gss_targ_ctx 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-KEY context exchange over a Kerberos V5 context exchange
would be: SHA-1( { SHA-1(CCM-KEY's initiator's token), SHA-
1(CCM-KEY's target's token)) }. Since the SHA-1 standard
mandates a 160 bit output, (20 octets), gss_targ_ctx is a fixed
length, 20 octet string.
* The subfield nonce.rand is set a random or pseudo random value.
It is provided so as to ensure more variability of the the mic
that GSS will calculate when CCM_MIC_unwrapped_init_token_t is
GSS_Wrap()ed into CCM_MIC_wrapped_init_token_t.
* The subfield nonce.ctx_sh_number is the identifier of the CCM-
MIC context relative to the CCM-BIND context (as identified by
gss_targ_ctx) that the initiator is assigning. The value for
ctx_sh_number is selected by the initiator such that it is
larger than any previous ctx_sh_number for the given
gss_targ_ctx. This way, the target need only keep track of the
largest ctx_sh_number received. Once ctx_sh_number has reached
the maximum value for an unsigned 32 bit integer, the given
gss_targ_ctx can no longer be used.
* Once the above fields are calculated, GSS_Wrap() is performed on
the CCM_MIC_unwrapped_init_token_t value, to produce a
CCM_MIC_wrapped_init_token_t value that becomes the initial
context token to send to the target.
4.8.2. 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.
4.8.2.1. Subsequent Initiator Context Initialization Token for CCM-MIC
As CCM-MIC has only one round trip for context token exchange, there
are no subsequent initiator context tokens.
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4.8.2.2. Response Token for CCM-MIC
The CCM response token, in XDR encoding is:
typedef enum {
CCM_OK = 0,
/*
* gss_targ_ctx was malformed.
*/
CCM_ERR_HANDLE_MALFORMED = 1,
/*
* GSS context corresponding to gss_targ_ctx expired.
*/
CCM_ERR_HANDLE_EXPIRED = 2,
/*
* gss_targ_ctx was not found.
*/
CCM_ERR_HANDLE_NOT_FOUND = 3,
/*
* The ctx_sh_number has already been received
* by the target. Or the maximum ctx_sh_number 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
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* by target.
*/
CCM_ERR_TKN_WRAP = 8,
/*
* The GSS_VerifyMIC() failed on the initiator. Not
* reported by target.
*/
CCM_ERR_TKN_VER_MIC = 9
} CCM_MIC_status_t;
/*
* GSS errors returned by the underlying mechanism
*/
typedef struct {
unsigned int gss_major;
unsigned int gss_minor;
} CCM_MIC_real_gss_err_t;
/*
* The response context token for CCM-MIC.
*/
typedef union switch (CCM_MIC_status status) {
case CCM_OK:
opaque mic_init_tkn<>;
case CCM_ERR_TKN_UNWRAP:
case CCM_ERR_TKN_GET_MIC:
CCM_real_gss_err_t gss_err;
default:
void;
} CCM_MIC_resp_t;
If a value of the status field is CCM_OK, then the CCM-MIC context
has been established on the target. The field mic_init_tkn is equal
to the output of GSS_GetMIC() (qop_req is CCM_REAL_QOP (1)) on the
entire and original token that came from the initiator. In other
words, the 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 mic_init_tkn 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 gss_err.gss_major and gss_err.minor are set to the major and
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minor GSS statuses as returned by GSS_Unwrap() or GSS_GetMIC(). The
values for the gss_major field are as defined in [RFC2744]. The
values for the gss_minor field are both mechanism dependent and
mechanism implemented dependent. They are nonetheless potentially
useful as debugging aids.
4.9. MIC Token for CCM-MIC
The MIC token for CCM-MIC is the same as the MIC token for CCM-BIND.
4.10. Wrap Token for CCM-MIC
The wrap token for CCM-MIC is the same as the wrap token for CCM-
BIND.
4.11. Context Deletion Token
The context deletion token for CCM-MIC is a zero length token.
4.12. Exported Context Token
The Exported context token for CCM-MIC is implementation defined.
4.13. Other Tokens for CCM-MIC
All other tokens are the same as corresponding tokens for CCM-BIND.
5. GSS Channel Bindings for Common Secure Channel Protocols
For CCM-KEY to be useful and secure, CCM-KEY MUST be used in
conjunction with channel bindings to bind GSS authentication at the
application layer to a lower layer in the network that provides
cryptographic session protection.
To date only network address type channel bindings have been defined
for GSS [RFC2743]. But the GSS also allows for channel bindings of
"transformations of encryption keys" [RFC2743]. The actual generic
representation of channel bindings is defined in the C-Bindings of
the GSS-API [RFC2744].
Modern secure transports generally define some quantity or quantities
which are either derived from the session keys (or from key exchange
material) or which are securely exchanged in such a way that both
peers of any one connection or association can arrive at the same
derived quantities, while a man-in-the-middle cannot make these
quantities match for both peers. Signatures of these quantities can
be exchanged to prove that there is no man-in-the-middle (because a
man-in-the-middle cannot cause them to be the same for both peers).
These quantities correspond to what the GSS terms "transformations of
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encryption keys" that are referred to in [RFC2743].
Where a secure transport clearly defines a session identifier
securely derived from session keys or key exchange material, that
identifier MUST be used as the GSS channel bindings data when CCM-
BIND is used to bind GSS to that transport.
This section defines four forms of "transformations of encryption
keys," one for IKEv1, one for IKEv2, one for SSHv2 and one for TLS.
All four forms are to be used as the value of the "application_data"
field of the gss_channel_bindings_struct type defined in [RFC2744].
5.1. GSS Channel Bindings for IKEv1
IKEv1 does not define a single value which can be used -- by both the
IPsec initiator and responder of an IPsec SA -- to identify a given
SA. IKEv1 does, however, define public values derived from the IKEv1
key exchange: 'HASH_I' and 'HASH_R'.
For IKEv1, the GSS channel bindings data to use with CCM-KEY consists
of the concatenation of HASH_I and HASH_R octet string values, in
that order, from the underlying IPsec session being bound to [IKEv1].
5.2. GSS Channel Bindings for IKEv2
IKEv2 peers assign and exchange 8-octet "Security Parameters Index"
(SPI) values, such that a pair of SPIs suffices to uniquely identify
a given IPsec security association.
For IKEv2 the GSS channel bindings data to use with CCM-KEY is simply
the concatenation of the SPIi and SPIr values, in that order, which
identify the IPsec SA being bound to.
5.3. GSS Channel Bindings for SSHv2
SSHv2 defines a session ID derived from the initial key exchange of
an SSHv2 connection; this value is not secret and is the same for
both the client and the server for any given connection.
For SSHv2 the GSS channel bindings data for use with CCM-KEY consists
of the SSHv2 session ID.
5.4. GSS Channel Bindings for TLS
XXX - This section is To Be Defined.
6. Use of Channel Bindings with CCM-BIND and SPKM
Whereas the Kerberos V5 mechanism specification [RFC1964] is quite
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detailed with respect to the use of GSS channel bindings, the same is
not true for SPKM, which merely provides a field named "channelId"
for passing channel bindings data, as octet strings, from initiators
to acceptors. No interpretation is given in RFC2025 for the value of
the channelId field. Therefore SPKM requires some clarification to
be usable with channel bindings and CCM-KEY: The channelId field of
SPKM Context-Data ASN.1 structure MUST be set to the checksum of the
channel bindings data that is defined for the Kerberos V5 mechanism
[RFC1964], using SHA-1 instead of MD5 as the hash algorithm.
[Note: This checksum can be computed independently of the GSS
language bindings used by the application, even though RFC1964
references the C-Bindings of the GSS-API [RFC2744] in the
construction of this checksum (read the RFC1964 text carefully).]
7. CCM-KEY and Anonymous IPsec
For sites that do not use IPsec, but use Kerberos V5, SPKM, or
LIPKEY, deploying IPsec, a PKI infrastructure and certificates for
use with IKE may prove quite difficult to deploy just for secure
application (e.g., NFS) performance improvements. Such sites could
avoid the need to deploy a PKI and certificates to all clients and
server by using "anonymous IPsec" for the application (e.g., NFS
with/ RPCSEC_GSS) and CCM-KEY.
Though there is no such thing as "anonymous IPsec," the effect can be
achieved by using self-signed certificates.
By using anonymous IPsec with the application and CCM-KEY, the full
benefit of offloading session cryptography from upper layer protocol
layer to the IP layer can be had without having to deploy an
authentication infrastructure for IPsec.
8. Other Protocol Issues for CCM
CCM-BIND is a trivial mechanism, and normally will return the same
major status code as the underlying real mechanism, including
GSS_S_COMPLETE as returned by GSS_Init_sec_context(). However, the
first time GSS_Init_sec_context is called on a CCM-BIND mechanism, if
the underlying real mechanism returns GSS_S_COMPLETE, CCM-BIND's
GSS_Init_sec_context() entry point MUST return GSS_S_CONTINUE_NEEDED
to the caller. This way, the initiator will receive another context
token from the target, even if the underlying real mechanism context
set up is done. The CCM-BIND initiator will need to record state
that indicates that the underlying mechanism has reached a completely
established state (and so is uninterested in any token the target
returns). This way, the initiator can process every token produced
by the target's GSS_Accept_sec_context() routine and so calculate
gss_targ_ctx value that matches that of the target.
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9. Implementation Issues
The "over the wire" aspects of CCM have been completely specified.
However, GSS is usually implemented as an Application Programming
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.
9.1. Management of gss_targ_ctx
The gss_targ_ctx 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.
9.2. 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.
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9.3. Initiating CCM-MIC Contexts
The key issue is how to associate an CCM-BIND established security
context with a new CCM-MIC context, There 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.
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
gss_targ_ctx 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(). The former are the context handles as
returned in a response token from the CCM target. 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 created 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 CCM_MIC_resp_t. 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 context_ptr;
} CCM_MIC_initiator_bootstrap_t;
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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 CCM_MIC_initiator_bootstrap_t. It would use
context_ptr to lookup the corresponding gss_targ_ctx in the
aforementioned gss_ctx_id_t to gss_targ_ctx mapping table. It
would then proceed to generate an output token encoded as XDR
type CCM_MIC_init_t, 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.
9.4. Accepting CCM-MIC Contexts
The CCM-MIC target receives an opaque gss_targ_ctx 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 mic_init_tkn field of the output token. By comparing
the ctx_sh_number in the initiator's token with highest value
recorded by the target, the target takes care to ensure that
initiator has not replayed a short token.
9.5. 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.
9.6. 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.
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9.7. GSS Status Codes
9.7.1. 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
whatever major and minor status codes the underlying mechanism
returns.
9.7.2. 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().
9.7.2.1. 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 CCM_MIC_status_t 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.
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------------------------------------------------------------------
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.
9.7.2.2. 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 CCM_MIC_status_t 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
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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
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
9.8. Channel Bindings on the Target
When an application invokes GSS_Accept_sec_context() on a CCM token,
it won't know if channel bindings are required or not. Of course, it
could inspect the OID of the input_token and determine the channel
bindings directly if it is a CCM-BIND token, but normally
applications will not parse the mechanism OID in an input token. And
in any case, such inspection for a CCM-MIC token provides no
information about channel bindings to the target application.
The application on the target will have to try
GSS_Accept_sec_context() without channel bindings. If the target CCM
mechanism requires channel bindings (as indicated by the
GSS_S_BAD_BINDINGS), then the application will have to re-invoke
GSS_Accept_sec_context() with the right channel bindings. If the
channel bindings are the wrong type, then the CCM mechanism will
indicate GSS_S_BAD_BINDINGS again. The application will have to
iterate through all the valid types of bindings. The application can
avoid this iteration if the bindings includes both, address and key
bindings if at all possible. The CCM mechanisms should use only
those parts of the application-provided bindings that they care for.
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10. Advice for NFSv4 Implementors
The NFSv4.0 specification does not mandate CCM, so clients and
servers 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.
11. Man in the Middle Attacks without CCM-KEY
In this example, NFS with/ RPCSEC_GSS will be the application, and
IPsec the secure channel.
Man in the middle (MITM) avoidance means making sure that the client
and server are the same at both layers, NFS and IPsec, but since the
principal names at the one layer will be radically different from the
names at the other, how can one be certain that there is no MITM at
the IPsec layer before leaving it to IPsec to provide session
protection to the NFS layer? The answer is to use channel bindings,
which, conceptually, are an exchange, at the NFS/GSS layer, of
signatures of the principal names or session ID/keys involved at the
IPsec layer.
Consider an attacker who can cause a client's IPsec stack to
establish an SA with the attacker, instead of the server intended by
the NFS layer (this is accomplished by spoofing the DNS server).
Suppose further that the attacker can fool the client's IPsec layer
without also fooling its NFS/RPCSEC_GSS layer (for example, if
Kerberos V5 is being used as the real mechanism, and avoids the use
of DNS to canonicalize the server principal name -- admittedly, this
avoidance is unlikely -- a DNS spoof attack will be detected by the
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NFS client, because the Kerberos Key Distribution Center (KDC)
generates tickets associated with pairs of principals, not host
names). Suppose that the attacker's host is in part of the site's
IPsec infrastructure (perhaps the attacker broke into that host).
Then the attacker might be able to act as a MITM between the client
and the server who gets all the plain text and even gets to modify
it, if CCM-NULL is wrapping Kerberos V5 at the RPCSEC_GSS level.
Both, the client and the server would see that IPsec is in use
between them, but they would each see a different ID for its IPsec
peer. Channel bindings are used to prove that the client and server
each see the same two peer names at the lower (in this case, IPsec)
layer, and therefore with CCM-KEY there is no MITM.
DNSSEC would of course defeat the attack, but DNSSEC was not, at the
time this document was written, in widespread use.
12. 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.
* 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
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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 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.
* 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. Furthermore, without channel
bindings mandated by CCM-KEY, it is not possible for the
initiator and target to enforce end to end channel security. 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, but without the use of CCM-KEY, the initiator and
target applications would have no way of knowing that.
* 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
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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. The use of CCM-KEY enforces
this binding.
* 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. Again, the use of CCM-KEY is one
way to assert this binding.
* The section entitled "CCM-KEY and Anonymous IPsec", suggests a
method for simulating anonymous IPsec via self-signed
certificates. If one is careless, this is will neuter all IPsec
authentication, a real problem for those applications not using
CCM-KEY. The use of the self-signed certificates in IPsec
should be restricted by port in the IPsec Security Policy
Database (SPD) only to those application using CCM-KEY. Note
however, that port selector support is OPTIONAL in IPsec.
* If an application is using IPsec and is not using CCM-KEY, 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-KEY's IPsec bindings use public SA information, and CCM-
ADDR's bindings are simply public network addresses. If the
secure channel is IPsec, and non-anonymous certificates are used
with IKE, then a MITM cannot spoof the target's and initiator's
IP addresses, because the attacker will presumably be unable to
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spoof the Certificate Authority that signed the certificates.
Thus, when IPsec is used as the secure channel, and non-
anonymous certificates are used with IKE, CCM-ADDR is as secure
as CCM-KEY.
* 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.
13. 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 TBD10. 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:
* Delete the "XXX Note 2 to RFC Editor: ..." paragraph.
* Replace occurrences of TBD2 through and including TBD10 withe
flavor number assignments from IANA.
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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-addr-krb5 1.3.6.1.5.5.TBD1.1.2. 0 rpc_gss_svc_none
1.2.840.113554.1.2.2
TBD5 ccm-key-krb5 1.3.6.1.5.5.TBD1.1.3. 0 rpc_gss_svc_none
1.2.840.113554.1.2.2
TBD6 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
TBD6 ccm-addr-spkm3 1.3.6.1.5.5.TBD1.1.2. 0 rpc_gss_svc_none
1.3.6.1.5.5.1.3
TBD7 ccm-key-spkm3 1.3.6.1.5.5.TBD1.1.3. 0 rpc_gss_svc_none
1.3.6.1.5.5.1.3
TBD8 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
TBD9 ccm-addr-lipkey 1.3.6.1.5.5.TBD1.1.2. 0 rpc_gss_svc_none
1.3.6.1.5.5.1.3
TBD10 ccm-addr-lipkey 1.3.6.1.5.5.TBD1.1.3. 0 rpc_gss_svc_none
1.3.6.1.5.5.1.3
14. 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, and Julian
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Satran, for their critical comments. Much of the text for the
"Security Considerations" section comes directly from David and Peng.
15. Normative References
[RFC1832]
R. Srinivasan, RFC1832, "XDR: External Data Representation
Standard", August, 1995.
[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.
[IKEv2]
C. Kaufman, draft-ietf-ipsec-ikev2-07.txt: "Internet Key
Exchange (IKEv2) Protocol," A work in progress, April 2003.
XXX - Note 3 to RFC Editor: In the event this work in progress
is not approved for publication when the CCM document is, then
the sections of the CCM document that refer to IKEv2 in a
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normative manner are to be removed for submission as a separate
document.
[SSHv2]
T. Ylonen et. al., draft-ietf-secsh-transport-15.txt: "SSH
Transport Layer Protocol," A work in progress, September 2002.
XXX - Note 4 to RFC Editor: In the event this work in progress
is not approved for publication when the CCM document is, then
the sections of the CCM document that refer to SSHv2 in a
normative manner are to be removed for submission as a separate
document.
16. 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
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.
17. Authors' Addresses
Mike Eisler
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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
18. 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
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
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
19. Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
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document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Expires: November 2003 [Page 30]
