draft-ietf-nfsv4-ccm-02.txt   draft-ietf-nfsv4-ccm-03.txt 
Network Working Group M. Eisler Network Working Group M. Eisler
Internet-Draft Network Appliance, Inc. Internet-Draft Network Appliance, Inc.
N. Williams N. Williams
Sun Microsystems, Inc. Sun Microsystems, Inc.
October 2003 July 2004
The Channel Conjunction Mechanism (CCM) for GSS The Channel Conjunction Mechanism (CCM) for GSS
draft-ietf-nfsv4-ccm-03
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance By submitting this Internet-Draft, I certify that any applicable
with all provisions of Section 10 of RFC2026. patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
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ABSTRACT ABSTRACT
This document describes a suite of new mechanisms under the GSS This document describes a suite of new mechanisms under the GSS
[RFC2743]. Some protocols, such as RPCSEC_GSS [RFC2203], use GSS to [RFC2743]. Some protocols, such as RPCSEC_GSS [RFC2203], use GSS to
authenticate every message transfer, thereby incurring significant authenticate every message transfer, thereby incurring significant
overhead due to the costs of cryptographic computation. While overhead due to the costs of cryptographic computation. While
hardware-based cryptographic accelerators can mitigate such overhead, hardware-based cryptographic accelerators can mitigate such overhead,
it is more likely that acceleration will be available for lower layer it is more likely that acceleration will be available for lower layer
protocols, such as IPsec [RFC2401] than for upper layer protocols protocols, such as IPsec [RFC2401] than for upper layer protocols
like RPCSEC_GSS. CCM can be used as a way to allow GSS mechanism- like RPCSEC_GSS. CCM can be used as a way to allow GSS mechanism-
independent upper layer protocols to leverage the data stream independent upper layer protocols to leverage the data stream
protections of lower layer protocols, without the inconvenience of protections of lower layer protocols, without the inconvenience of
modifying the upper layer protocol to do so. modifying the upper layer protocol to do so.
TABLE OF CONTENTS TABLE OF CONTENTS
1. Conventions Used in this Document . . . . . . . . . . . . . . . 3 1. Conventions Used in this Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Example Application of CCM . . . . . . . . . . . . . . . . . 4 3.1. Example Application of CCM . . . . . . . . . . . . . . . . . 4
3.2. A Suite of CCM Mechanisms . . . . . . . . . . . . . . . . . . 5 3.2. A Suite of CCM Mechanisms . . . . . . . . . . . . . . . . . . 4
3.3. QOPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3. QOPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Token Formats . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Token Formats . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Mechanism Object Identifier . . . . . . . . . . . . . . . . . 6 4.1. Mechanism Object Identifier . . . . . . . . . . . . . . . . . 5
4.2. Tokens for the CCM-BIND mechanisms . . . . . . . . . . . . . 6 4.2. Tokens for the CCM-BIND mechanisms . . . . . . . . . . . . . 6
4.3. Context Establishment Tokens for CCM-BIND Mechanisms . . . . 6 4.2.1. Context Establishment Tokens for CCM-BIND Mechanisms . . . 6
4.3.1. Initial Context Token for CCM-BIND . . . . . . . . . . . . 7 4.2.1.1. Initial Context Token for CCM-BIND . . . . . . . . . . . 6
4.3.2. Subsequent Context Tokens for CCM-BIND . . . . . . . . . . 7 4.2.1.2. Subsequent Context Tokens for CCM-BIND . . . . . . . . . 6
4.3.2.1. Subsequent Initiator Context Initialization Token for 4.2.2. Post Context Establishment Token Formats . . . . . . . . . 8
CCM-BIND . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2.2.1. MIC Token for CCM-BIND . . . . . . . . . . . . . . . . . 9
4.3.2.2. Response Token for CCM-BIND . . . . . . . . . . . . . . . 7 4.2.2.2. Wrap Token for CCM-BIND . . . . . . . . . . . . . . . . . 9
4.4. MIC Token for CCM-BIND . . . . . . . . . . . . . . . . . . . 7 4.2.3. Other Tokens for CCM-BIND . . . . . . . . . . . . . . . . . 9
4.5. Wrap Token for CCM-BIND . . . . . . . . . . . . . . . . . . . 7 4.3. Tokens for CCM-MIC . . . . . . . . . . . . . . . . . . . . . 9
4.6. Other Tokens for CCM-BIND . . . . . . . . . . . . . . . . . . 8 4.3.1. Context Establishment Tokens for CCM-MIC . . . . . . . . . 9
4.7. Tokens for CCM-MIC . . . . . . . . . . . . . . . . . . . . . 8 4.3.1.1. Initial Context Token for CCM-MIC . . . . . . . . . . . . 9
4.8. Context Establishment Tokens for CCM-MIC . . . . . . . . . . 8 4.3.1.2. Subsequent Context Tokens for CCM-MIC . . . . . . . . . 11
4.8.1. Initial Context Token for CCM-MIC . . . . . . . . . . . . . 8 4.3.1.2.1. Subsequent Initiator Context Token for CCM-MIC . . . 11
4.8.2. Subsequent Context Tokens for CCM-MIC . . . . . . . . . . . 9 4.3.1.2.2. Response Token for CCM-MIC . . . . . . . . . . . . . 11
4.8.2.1. Subsequent Initiator Context Initialization Token for 4.3.2. MIC Token for CCM-MIC . . . . . . . . . . . . . . . . . . 13
CCM-MIC . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.3.3. Wrap Token for CCM-MIC . . . . . . . . . . . . . . . . . 13
4.8.2.2. Response Token for CCM-MIC . . . . . . . . . . . . . . 10 4.3.4. Context Deletion Token . . . . . . . . . . . . . . . . . 13
4.9. MIC Token for CCM-MIC . . . . . . . . . . . . . . . . . . . 12 4.3.5. Exported Context Token . . . . . . . . . . . . . . . . . 13
4.10. Wrap Token for CCM-MIC . . . . . . . . . . . . . . . . . . 12 4.3.6. Other Tokens for CCM-MIC . . . . . . . . . . . . . . . . 13
4.11. Context Deletion Token . . . . . . . . . . . . . . . . . . 12 5. Implementation Issues . . . . . . . . . . . . . . . . . . . . 13
4.12. Exported Context Token . . . . . . . . . . . . . . . . . . 12 5.1. Management of ccmMicCcmBindCtxHandle . . . . . . . . . . . 14
4.13. Other Tokens for CCM-MIC . . . . . . . . . . . . . . . . . 12 5.2. CCM-BIND Versus CCM-MIC . . . . . . . . . . . . . . . . . . 14
5. GSS Channel Bindings for Common Secure Channel Protocols . . 12 5.3. Initiating CCM-MIC Contexts . . . . . . . . . . . . . . . . 14
5.1. GSS Channel Bindings for IKEv1 . . . . . . . . . . . . . . 13 5.4. Accepting CCM-MIC Contexts . . . . . . . . . . . . . . . . 16
5.2. GSS Channel Bindings for IKEv2 . . . . . . . . . . . . . . 13 5.5. Non-Token Generating GSS-API Routines . . . . . . . . . . . 16
5.3. GSS Channel Bindings for SSHv2 . . . . . . . . . . . . . . 13 5.6. CCM-MIC and GSS_Delete_sec_context() . . . . . . . . . . . 16
5.4. GSS Channel Bindings for TLS . . . . . . . . . . . . . . . 13 5.7. GSS Status Codes . . . . . . . . . . . . . . . . . . . . . 16
6. Use of Channel Bindings with CCM-BIND and SPKM . . . . . . . 14 5.7.1. Status Codes for CCM-BIND . . . . . . . . . . . . . . . . 16
7. CCM-KEY and Anonymous IPsec . . . . . . . . . . . . . . . . . 14 5.7.2. Status Codes for CCM-MIC . . . . . . . . . . . . . . . . 17
8. Other Protocol Issues for CCM . . . . . . . . . . . . . . . . 14 5.7.2.1. CCM-MIC: GSS_Accept_sec_context() status codes . . . . 17
9. Implementation Issues . . . . . . . . . . . . . . . . . . . . 15 5.7.2.2. CCM-MIC: GSS_Init_sec_context() status codes . . . . . 18
9.1. Management of gss_targ_ctx . . . . . . . . . . . . . . . . 15 6. Advice for NFSv4 Implementors . . . . . . . . . . . . . . . . 19
9.2. CCM-BIND Versus CCM-MIC . . . . . . . . . . . . . . . . . . 15 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9.3. Initiating CCM-MIC Contexts . . . . . . . . . . . . . . . . 16 8. CCM XDR Description . . . . . . . . . . . . . . . . . . . . . 22
9.4. Accepting CCM-MIC Contexts . . . . . . . . . . . . . . . . 17 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9.5. Non-Token Generating GSS-API Routines . . . . . . . . . . . 17 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
9.6. CCM-MIC and GSS_Delete_sec_context() . . . . . . . . . . . 17 11. Normative References . . . . . . . . . . . . . . . . . . . . 25
9.7. GSS Status Codes . . . . . . . . . . . . . . . . . . . . . 18 12. Informative References . . . . . . . . . . . . . . . . . . . 26
9.7.1. Status Codes for CCM-BIND . . . . . . . . . . . . . . . . 18 13. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 27
9.7.2. Status Codes for CCM-MIC . . . . . . . . . . . . . . . . 18 14. IPR Notices . . . . . . . . . . . . . . . . . . . . . . . . 27
9.7.2.1. CCM-MIC: GSS_Accept_sec_context() status codes . . . . 18 15. Copyright Notice . . . . . . . . . . . . . . . . . . . . . . 28
9.7.2.2. CCM-MIC: GSS_Init_sec_context() status codes . . . . . 19
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 . . . . . . . . . . . . . . . . . . . . . 29
18. IPR Notices . . . . . . . . . . . . . . . . . . . . . . . . 29
19. Copyright Notice . . . . . . . . . . . . . . . . . . . . . . 29
1. Conventions Used in this Document 1. Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Introduction 2. Introduction
The GSS framework provides a general means for authenticating clients The GSS framework provides a general means for authenticating clients
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CCM is a "wrapper" mechanism over the set of all other GSS CCM is a "wrapper" mechanism over the set of all other GSS
mechanisms. When CCM creates a context, it invokes an underlying mechanisms. When CCM creates a context, it invokes an underlying
mechanism to create a child context. CCM determines the underlying mechanism to create a child context. CCM determines the underlying
mechanism by examining the mechanism object identifier (OID) that it mechanism by examining the mechanism object identifier (OID) that it
is called with. The prefix will always be the OID of CCM, and the 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 suffix will be the OID of the underlying mechanism. The context
initiation and acceptance entry points of CCM wrap the resulting the initiation and acceptance entry points of CCM wrap the resulting the
context tokens with a CCM header. context tokens with a CCM header.
XXX - Note, as currently defined CCM-BIND has a problem with replay
attacks. Let's suppose the target does not implement a cache of
previously accepted context tokens. An attacker can replay the CCM-
BIND initial context token, and the target will accept it. What is
needed is proof that the initiator actually knows the context session
key. A future version of this i-d will specify a round trip for CCM-
BIND (and CCM-MIC) that will force the initiator to sign a nonce from
the target. See [Kasslin] for more information on the attack.
3.1. Example Application of CCM 3.1. Example Application of CCM
Let us use RPCSEC_GSS and NFSv4 [RFC3530] as our example. Basic Let us use RPCSEC_GSS and NFSv4 [RFC3530] as our example. Basic
understanding of the RPCSEC_GSS protocol is assumed. If an NFSv4 understanding of the RPCSEC_GSS protocol is assumed. If an NFSv4
client uses the wrong security mechanism, the server returns the client uses the wrong security mechanism, the server returns the
NFS4ERR_WRONGSEC error. The client can then use NFSv4's SECINFO NFS4ERR_WRONGSEC error. The client can then use NFSv4's SECINFO
operation to ask the server which GSS mechanism to use. operation to ask the server which GSS mechanism to use.
Let us say the client and server are using Kerberos V5 [RFC1964] to Let us say the client and server are using Kerberos V5 [RFC1964] to
secure the traffic. Suppose the TCP connection NFSv4 uses is secured secure the traffic. Suppose the TCP connection NFSv4 uses is secured
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Enter CCM. The server detects that the connection is protected with Enter CCM. The server detects that the connection is protected with
IPsec. Via SECINFO, the client is informed that it should use IPsec. Via SECINFO, the client is informed that it should use
CCM/Kerberos V5. Via the RPCSEC_GSS protocol, the server CCM/Kerberos V5. Via the RPCSEC_GSS protocol, the server
authenticates the end-user on the client with Kerberos V5. The authenticates the end-user on the client with Kerberos V5. The
context tokens exchanged over RPCSEC_GSS are wrapped inside CCM context tokens exchanged over RPCSEC_GSS are wrapped inside CCM
tokens. tokens.
3.2. A Suite of CCM Mechanisms 3.2. A Suite of CCM Mechanisms
CCM consists of a suite of GSS mechanisms. CCM-NULL, CCM-ADDR, and CCM consists of a suite of GSS mechanisms. GSS can support a concept
CCM-KEY bind a GSS mechanism context to a secure channel via GSS call channel bindings, where a GSS mechanism context is bound to a
channel bindings (see section 1.1.6 of RFC2743). As noted in secure channel (see section 1.1.6 of RFC2743). As noted in RFC2743,
RFC2743, the purpose of channel bindings are to limit the scope the purpose of channel bindings is to limit the scope within which an
within which an intercepted GSS context token can be used by an intercepted GSS context token can be used by an attacker. Non-null
attacker. CCM-KEY requires the use of channel bindings that are channel bindings can be derived from the secure channel's encryption
derived from the secure channel's encryption keys. CCM-ADDR requires keys or derived from the network addresses associated with the secure
the use of channel bindings that are derived from network addresses channel. For environments where it is not feasible to use key-based
associated with the secure channel. For environments where it is not channel bindings (e.g., the programming interfaces to get them are
feasible to use key-based channel bindings (e.g., the programming not available) or address-based channel bindings (e.g., the secure
interfaces to get them are not available) or address-based channel channel may be constructed over a path that requires the use of
bindings (e.g., the secure channel may be constructed over a path Network Address Translation), CCM-NULL is defined. CCM-NULL requires
that requires the use of Network Address Translation), CCM-NULL is the use of null channel bindings.
also defined. CCM-NULL requires the use of null channel bindings.
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 As discussed later in this document CCM-MIC exists for the purpose of
optimizing the use of CCM. optimizing the use of CCM.
Implementations that claim compliance with this document are REQUIRED Implementations that claim compliance with this document are REQUIRED
to implement CCM-KEY and CCM-MIC. CCM-NULL and CCM-ADDR to implement CCM-NULL and CCM-MIC. Specifications that make normative
implementation are OPTIONAL. Specifications that make normative
references to CCM are free to mandate any subset of the suite CCM references to CCM are free to mandate any subset of the suite CCM
mechanisms. 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 CCM-MIC is intended to reduce the instances of full GSS context
establishment to a per- {initiator principal, target} tuple. CCM-MIC establishment to a per- {initiator principal, target} tuple. CCM-MIC
is used to establish a new context by proving that the initiator and is used to establish a new context by proving that the initiator and
target both have a previously established, unexpired GSS context; the target both have a previously established, unexpired GSS context; the
proof is accomplished by exchanging MICs made with the previously proof is accomplished by exchanging MICs made with the previously
established GSS context. The CCM-MIC context creation entry points established GSS context. The CCM-MIC context creation entry points
utilize the CCM_REAL_QOP (discussed later Overview section) in the utilize the CCM_REAL_QOP (discussed in the next section) in the value
value to generate and verify the MICs. The type of channel bindings to generate and verify the MICs.
used when initiating CCM-MIC contexts MUST match that used when
creating the previously established context.
3.3. QOPs 3.3. QOPs
The CCM mechanisms provide two QOPs: the default QOP (0) that amounts 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 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 maps to the default QOP of the underlying GSS mechanism. When
tokens for CCM are a string of 4 octets, each zero filled. When qop_req is 0:
qop_req is 0, the wrap output token for CCM is equal to the
concatenation of the input token and a single octet (which is equal * The MIC token for CCM is always a single octet, of value zero.
to 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 4. Token Formats
This section discusses the protocol visible tokens that GSS consumers This section discusses the protocol visible tokens that GSS consumers
exchange when using CCM. exchange when using CCM.
4.1. Mechanism Object Identifier 4.1. Mechanism Object Identifier
There are two classes of Mechanism object identifiers (OIDs) for CCM. There are two classes of Mechanism Object Identifiers (OIDs) for CCM.
The first class consists of the channel binding specific OIDs, and The first class consists of the channel binding specific OIDs, and
will be referred to as the CCM-BIND mechanisms: will be referred to as the CCM-BIND mechanisms. This document defines
one such mechanism:
{iso(1)identified-organization(3)dod(6)internet(1)security(5) { iso(1) identified-organization(3) dod(6) internet(1)
mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-null(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) The above object identifier is not a complete mechanism OID. A
mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-addr(2)} 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].
{iso(1)identified-organization(3)dod(6)internet(1)security(5) Future extensions to CCM may add non-null channel binding mechanisms
mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-key(3)} under the ccm-bind(1) node in the OID space.
The above three object identifiers are not complete mechanism OIDs. The second class consists of a single OID for the CCM-MIC mechanism.
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) { iso(1) identified-organization(3) dod(6) internet(1)
mechanisms(5)ccm-family(TBD1)ccm-mic(2)} security(5) mechanisms(5) ccm-family(TBD1) ccm-mic(2) }
The CCM-MIC OID is a complete mechanism OIDs, and is not a prefix. 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 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. not require ASN.1 for the mechanism specific part of a token.
4.2. Tokens for the CCM-BIND mechanisms 4.2. Tokens for the CCM-BIND mechanisms
4.3. Context Establishment Tokens for CCM-BIND Mechanisms 4.2.1. Context Establishment Tokens for CCM-BIND Mechanisms
The CCM-BIND context establishment tokens are simple wrappers around The CCM-BIND context establishment tokens are simple wrappers around
a real GSS mechanism's tokens. The CCM-BIND mechanisms use the same a real GSS mechanism's tokens. The CCM-BIND mechanisms can use one
number context token exchanges as required by they underlying real more context token exchange than the underlying real mechanism. This
mechanism. 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.
4.3.1. Initial Context Token for CCM-BIND 4.2.1.1. Initial Context Token for CCM-BIND
GSS requires that the initial context token from the initiator to the 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 target use the format as described in section 3.1 of RFC2743. The
format consists of a mechanism independent prefix, and a mechanism format consists of a mechanism independent prefix, and a mechanism
dependent suffix. The mechanism independent token includes the dependent suffix. The mechanism independent token includes the
MechType field. The MechType MUST be equal to the OID of CCM-NULL, 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 The mechanism dependent portion of the Initial Context Token is
Context Token is always equal to the full InitialContextToken as always equal to the full InitialContextToken as returned by the
returned by the underlying real mechanism. This will include yet underlying real mechanism. This will include yet another MechType,
another MechType, which will have the underlying mechanism's OID. which will have the underlying mechanism's OID.
4.3.2. Subsequent Context Tokens for CCM-BIND 4.2.1.2. Subsequent Context Tokens for CCM-BIND
A subsequent context token can be any subsequent context token from A subsequent context token can be any subsequent context token from
the initiator context initialization entry point, or any response the initiator context initialization entry point, or any response
context from the target's context acceptance entry point. The GSS context from the target's context acceptance entry point. The GSS
specification [RFC2743] does not prescribe any format. specification [RFC2743] does not prescribe any format.
4.3.2.1. Subsequent Initiator Context Initialization Token for CCM-BIND 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:
A SubsequentContextToken for a CCM-BIND mechanism is equal to that enum ccmVerifyState {
returned by the initiator's context initialization routine of the CCM_UNVERIFIED = 0,
underlying real mechanism. CCM_VERIFY_FAILED = 1,
CCM_VERIFIED = 2
};
4.3.2.2. Response Token for CCM-BIND struct ccmBindSubCtxTknTargToInit {
ccmVerifyState ccmBindStatus;
opaque ccmBindRealToken<>;
opaque ccmBindNonce<>;
};
The response token for a CCM-BIND mechanism is equal to that returned struct ccmBindSubCtxTknInitToTarg {
by the target's context acceptance routine of the underlying real opaque ccmBindRealToken<>;
mechanism. opaque ccmBindMic<>;
};
4.4. MIC Token for CCM-BIND 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.
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
4.2.2.1. MIC Token for CCM-BIND
This token corresponds to the PerMsgToken type as defined in section 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 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 PerMsgToken is one octet in length with a value of zero. When the
that calls GSS_GetMIC() with the default QOP will thus produce an qop_req is CCM_REAL_QOP (1), then PerMsgToken is whatever the
octet string of zero length. underlying real mechanism returns from GSS_GetMIC() when passed the
default QOP value (0).
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 4.2.2.2. Wrap Token for CCM-BIND
This token corresponds to the SealedMessage type as defined in This token corresponds to the SealedMessage type as defined in
section 3.1 of RFC2743. When the qop_req is the default QOP (0), 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 then the SealedMessage token is equal to the unmodified input to
GSS_Wrap(). 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 When the qop_req is CCM_REAL_QOP (1), then SealedMessage is whatever
the underlying real mechanism returns from GSS_Wrap(), when passed the underlying real mechanism returns from GSS_Wrap(), when passed
the default QOP value (0). the default QOP value (0).
4.6. Other Tokens for CCM-BIND 4.2.3. Other Tokens for CCM-BIND
All other tokens are what the real underlying mechanism returns as a All other tokens are what the real underlying mechanism returns as a
token. token.
4.7. Tokens for CCM-MIC 4.3. Tokens for CCM-MIC
4.8. Context Establishment Tokens for CCM-MIC 4.3.1. Context Establishment Tokens for CCM-MIC
4.8.1. Initial Context Token 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 The initial context token from the initiator to the target uses the
format as described in section 3.1 of RFC2743. The format consists format as described in section 3.1 of RFC2743. The format consists
of a mechanism independent prefix, and a mechanism dependent suffix. of a mechanism independent prefix, and a mechanism dependent suffix.
The mechanism independent token includes the MechType field. The The mechanism independent token includes the MechType field. The
MechType MUST be equal to the OID of CCM-MIC. RFC2743 refers to the MechType MUST be equal to the OID of CCM-MIC. RFC2743 refers to the
mechanism dependent token as the innerContextToken. This is the mechanism dependent token as the innerContextToken. This is the
CCM-MIC specific token and is XDR [RFC1832] encoded as follows, using CCM-MIC specific token and is XDR [RFC1832] encoded as follows, using
XDR description language: XDR description language:
typedef struct { struct ccmMicUnWrappedInitToken {
unsigned int ctx_sh_number; unsigned int ctxMicIndex;
unsigned int rand; opaque ccmMicCcmBindCtxHandle[20];
} CCM_nonce_t; opaque ccmMicNonce<>;
};
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 * The result of ccmMicUnWrappedInitToken after
* Invoking GSS_GetMIC() on it. qop_req is CCM_REAL_QOP, and * Invoking GSS_GetMIC() on it. qop_req is CCM_REAL_QOP, and
* conf_flag is FALSE. * conf_flag is FALSE.
*/ */
typedef opaque CCM_MIC_wrapped_init_token_t<>; typedef opaque ccmBindMicWrappedInitToken<>;
Once an initiator has established an initial CCM context with a Once an initiator has established an initial CCM context with a
target via a CCM-BIND mechanism, the additional contexts can be target via a CCM-BIND mechanism, the additional contexts can be
established via the CCM-MIC mechanism. The disadvantage of re- established via the CCM-MIC mechanism. The disadvantage of
establishing additional contexts via the CCM-BIND route is that the establishing additional contexts via the CCM-BIND route is that the
underlying mechanism context set up must be repeated, which can be underlying mechanism context set up must be repeated, which can be
expensive. Whereas, the CCM-MIC mechanism route merely requires that expensive. Whereas, the CCM-MIC mechanism route merely requires that
the first CCM context's underlying mechanism context be available to the first CCM context's underlying mechanism context be available to
produce an integrity checksum. The initial context token for CCM-MIC produce an integrity checksum. The initial context token for CCM-MIC
is computed as follows. is computed as follows.
* The gss_targ_ctx is computed as the SHA-1 checksum of the * The ccmMicCcmBindCtxHandle is computed as the SHA-1 checksum of
concatenation of SHA-1 [FIPS] checksums of the context tokens the concatenation of SHA-1 [FIPS] checksums of the context
exchanged by the CCM-BIND mechanism in the order in which they tokens exchanged by the CCM-BIND mechanism in the order in which
were processed. For example, the context handle identifier for a they were processed. For example, the context handle identifier
CCM-KEY context exchange over a Kerberos V5 context exchange for a CCM-NULL context exchange over a Kerberos V5 context
would be: SHA-1( { SHA-1(CCM-KEY's initiator's token), SHA- exchange would be:
1(CCM-KEY's target's token)) }. Since the SHA-1 standard SHA-1( {
mandates a 160 bit output, (20 octets), gss_targ_ctx is a fixed SHA-1(CCM-NULL's first initiator token),
length, 20 octet string. 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 subfield nonce.rand is set a random or pseudo random value. * The field ccmMicNonce is set a random or pseudo random value. It
It is provided so as to ensure more variability of the the mic MUST have length greater than or equal to that of ccmBindNonce
that GSS will calculate when CCM_MIC_unwrapped_init_token_t is value the target gave the server when the CCM-BIND context was
GSS_Wrap()ed into CCM_MIC_wrapped_init_token_t. 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 subfield nonce.ctx_sh_number is the identifier of the CCM- * The field ctxMicIndex is the identifier of the CCM-MIC context
MIC context relative to the CCM-BIND context (as identified by relative to the CCM-BIND context (as identified by
gss_targ_ctx) that the initiator is assigning. The value for ccmMicCcmBindCtxHandle) that the initiator is assigning. The
ctx_sh_number is selected by the initiator such that it is value for ctxMicIndex is selected by the initiator such that it
larger than any previous ctx_sh_number for the given is larger than any previous ctxMicIndex for the given
gss_targ_ctx. This way, the target need only keep track of the ccmMicCcmBindCtxHandle. This way, the target need only keep
largest ctx_sh_number received. Once ctx_sh_number has reached track of the largest ctxMicIndex received. Once ctxMicIndex has
the maximum value for an unsigned 32 bit integer, the given reached the maximum value for an unsigned 32 bit integer, the
gss_targ_ctx can no longer be used. given ccmMicCcmBindCtxHandle can no longer be used.
* Once the above fields are calculated, GSS_Wrap() is performed on * Once the above fields are calculated, GSS_Wrap() is performed on
the CCM_MIC_unwrapped_init_token_t value, to produce a the ccmMicUnWrappedInitToken value, to produce a
CCM_MIC_wrapped_init_token_t value that becomes the initial ccmBindMicWrappedInitToken value that becomes the initial
context token to send to the target. context token to send to the target.
4.8.2. Subsequent Context Tokens for CCM-MIC 4.3.1.2. Subsequent Context Tokens for CCM-MIC
A subsequent context token can be any subsequent context token from A subsequent context token can be any subsequent context token from
the initiator context initialization entry point, or any response the initiator context initialization entry point, or any response
context from the target's context acceptance entry point. The GSS context from the target's context acceptance entry point. The GSS
specification [RFC2743] does not prescribe any format. specification [RFC2743] does not prescribe any format.
4.8.2.1. Subsequent Initiator Context Initialization Token for CCM-MIC 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 As CCM-MIC has only one round trip for context token exchange, there
are no subsequent initiator context tokens. are no subsequent initiator context tokens.
4.8.2.2. Response Token for CCM-MIC 4.3.1.2.2. Response Token for CCM-MIC
The CCM response token, in XDR encoding is: The CCM response token, in XDR encoding is:
typedef enum { enum ccmMicStatus {
CCM_OK = 0, CCM_OK = 0,
/* /*
* gss_targ_ctx was malformed. * ccmMicCcmBindCtxHandle was malformed.
*/ */
CCM_ERR_HANDLE_MALFORMED = 1, CCM_ERR_HANDLE_MALFORMED = 1,
/* /*
* GSS context corresponding to gss_targ_ctx expired. * The GSS context corresponding to
* ccmMicCcmBindCtxHandle has expired.
*/ */
CCM_ERR_HANDLE_EXPIRED = 2, CCM_ERR_HANDLE_EXPIRED = 2,
/* /*
* gss_targ_ctx was not found. * ccmMicCcmBindCtxHandle was not found.
*/ */
CCM_ERR_HANDLE_NOT_FOUND = 3, CCM_ERR_HANDLE_NOT_FOUND = 3,
/* /*
* The ctx_sh_number has already been received * The ctxMicIndex has already been received
* by the target. Or the maximum ctx_sh_number has * by the target. Or the maximum ctxMicIndex has
* been previously received. * been previously received.
*/ */
CCM_ERR_TKN_REPLAY = 4, CCM_ERR_TKN_REPLAY = 4,
/* /*
* Channel binding type mismatch between CCM-BIND context * Channel binding type mismatch between CCM-BIND context
* and the CCM-MIC initial context. * and the CCM-MIC initial context.
*/ */
CCM_ERR_CHAN_MISMATCH = 5, CCM_ERR_CHAN_MISMATCH = 5,
skipping to change at page 11, line 18 skipping to change at page 12, line 34
CCM_ERR_TKN_WRAP = 8, CCM_ERR_TKN_WRAP = 8,
/* /*
* The GSS_VerifyMIC() failed on the initiator. Not * The GSS_VerifyMIC() failed on the initiator. Not
* reported by target. * reported by target.
*/ */
CCM_ERR_TKN_VER_MIC = 9 CCM_ERR_TKN_VER_MIC = 9
} CCM_MIC_status_t; };
/* /*
* GSS errors returned by the underlying mechanism * GSS errors returned by the underlying mechanism
*/ */
typedef struct { struct ccmMicRealGssErr {
unsigned int gss_major; unsigned int ccmMicGssMajor;
unsigned int gss_minor; unsigned int ccmMicGssMinor;
} CCM_MIC_real_gss_err_t; };
/* /*
* The response context token for CCM-MIC. * The response context token for CCM-MIC.
*/ */
typedef union switch (CCM_MIC_status status) { union ccmMicResp switch (ccmMicStatus status) {
case CCM_OK: case CCM_OK:
opaque mic_init_tkn<>; opaque ccmMicRespInitTkn<>;
case CCM_ERR_TKN_UNWRAP: case CCM_ERR_TKN_UNWRAP:
case CCM_ERR_TKN_GET_MIC: case CCM_ERR_TKN_GET_MIC:
CCM_real_gss_err_t gss_err; ccmMicRealGssErr ccmMicGssErr;
default: default:
void; void;
} CCM_MIC_resp_t; };
If a value of the status field is CCM_OK, then the CCM-MIC context 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 has been established on the target. The field ccmMicRespInitTkn is
to the output of GSS_GetMIC() (qop_req is CCM_REAL_QOP (1)) on the equal to the output of GSS_GetMIC() (qop_req is CCM_REAL_QOP (1)) on
entire and original token that came from the initiator. In other the entire and first token that came from the initiator. In other
words, the input_token value to GSS_Accept_sec_context(). This is words, the first input_token value to GSS_Accept_sec_context(). This
necessary because the inner token from the initiator is wrapped with is necessary because the inner token from the initiator is wrapped
GSS_Wrap(), and thus contains a MIC. If we performed GSS_GetMIC() on with GSS_Wrap(), and thus contains a MIC. If we performed
the unwrapped inner token, then for some underlying mechanisms, we GSS_GetMIC() on the unwrapped inner token, then for some underlying
would end up with a mic_init_tkn in the response token equal to what mechanisms, we would end up with a ccmMicRespInitTkn in the response
was embedded in the request token. 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, 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 then ccmMicGssErr.ccmMicGssMajor and ccmMicGssErr.ccmMicGssMinor are
minor GSS statuses as returned by GSS_Unwrap() or GSS_GetMIC(). The set to the major and minor GSS statuses as returned by GSS_Unwrap()
values for the gss_major field are as defined in [RFC2744]. The or GSS_GetMIC(). The values for the ccmMicGssMajor field are as
values for the gss_minor field are both mechanism dependent and defined in [RFC2744]. The values for the ccmMicGssMinor field are
mechanism implemented dependent. They are nonetheless potentially both mechanism dependent and mechanism implementation dependent.
useful as debugging aids. They are nonetheless potentially useful as debugging aids.
4.9. MIC Token for CCM-MIC 4.3.2. MIC Token for CCM-MIC
The MIC token for CCM-MIC is the same as the MIC token for CCM-BIND. The MIC token for CCM-MIC is the same as the MIC token for CCM-BIND.
4.10. Wrap Token for CCM-MIC 4.3.3. Wrap Token for CCM-MIC
The wrap token for CCM-MIC is the same as the wrap token for CCM- The wrap token for CCM-MIC is the same as the wrap token for CCM-
BIND. BIND.
4.11. Context Deletion Token 4.3.4. Context Deletion Token
The context deletion token for CCM-MIC is a zero length token. The context deletion token for CCM-MIC is a zero length token.
4.12. Exported Context Token 4.3.5. Exported Context Token
The Exported context token for CCM-MIC is implementation defined. The Exported context token for CCM-MIC is implementation defined.
4.13. Other Tokens for CCM-MIC 4.3.6. Other Tokens for CCM-MIC
All other tokens are the same as corresponding tokens for CCM-BIND. All other tokens are the same as corresponding tokens for CCM-BIND.
5. GSS Channel Bindings for Common Secure Channel Protocols 5. Implementation Issues
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
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
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.
9. Implementation Issues
The "over the wire" aspects of CCM have been completely specified. The "over the wire" aspects of CCM have been completely specified.
However, GSS is usually implemented as an Application Programming However, GSS is usually implemented as an Application Programming
Interface (the GSS-API), and security mechanisms are often Interface (the GSS-API), and security mechanisms are often
implemented as modules that are plugged into the GSS-API. It is implemented as modules that are plugged into the GSS-API. It is
useful to discuss implementation issues and workable resolutions. useful to discuss implementation issues and workable resolutions.
The reader is cautioned that the authors have not implemented CCM, so The reader is cautioned that the authors have not implemented CCM, so
what follows is at best a series of educated guesses. what follows is at best a series of educated guesses.
9.1. Management of gss_targ_ctx 5.1. Management of ccmMicCcmBindCtxHandle
The gss_targ_ctx value is computed by the initiator and target based The ccmMicCcmBindCtxHandle value is computed by the initiator and
on SHA-1 computations of the CCM-BIND context tokens. There is a target based on SHA-1 computations of the CCM-BIND context tokens.
space/time trade off between the initiator and target storing the There is a space/time trade off between the initiator and target
sequence of context tokens until needed by CCM-BIND, versus computing storing the sequence of context tokens until needed by CCM-BIND,
the SHA-1 checksums and then disposing of the context tokens when versus computing the SHA-1 checksums and then disposing of the
CCM-BIND no longer needs them. If it is likely there will be CCM-MIC context tokens when CCM-BIND no longer needs them. If it is likely
contexts created for the CCM-BIND context, and if the sequence of there will be CCM-MIC contexts created for the CCM-BIND context, and
context tokens requires more space than a 20 octet SHA-1 value, then if the sequence of context tokens requires more space than a 20 octet
the tradeoff is obvious. SHA-1 value, then the tradeoff is obvious.
Since the bit space of all possible sequences of CCM-BIND context 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, tokens is larger than the 160 bit space of possible SHA-1 checksums,
in theory two or more different CCM-BIND contexts will produce in theory two or more different CCM-BIND contexts will produce
produce the same SHA-1 context, and thus for CCM-MIC context produce the same SHA-1 context, and thus for CCM-MIC context
initiation, there will be ambiguity as to which CCM-BIND context the initiation, there will be ambiguity as to which CCM-BIND context the
initiator is binding to. The target can resolve this ambiguity by initiator is binding to. The target can resolve this ambiguity by
attempting to unwrap the inner context token from the CCM-MIC attempting to unwrap the inner context token from the CCM-MIC
initiator for each matching CCM-BIND context. In theory no more than initiator for each matching CCM-BIND context. In theory no more than
one GSS_Unwrap() attempt for each matching CCM-BIND context will one GSS_Unwrap() attempt for each matching CCM-BIND context will
succeed. If multiple succeed, then clearly the underlying mechanism succeed. If multiple succeed, then clearly the underlying mechanism
is doing poor job at generating "unique" session keys. CCM is doing poor job at generating "unique" session keys. CCM
implementations that detect this SHOULD log it so that the problem in implementations that detect this SHOULD log it so that the problem in
the underlying mechanism can be discovered and fixed. the underlying mechanism can be discovered and fixed.
9.2. CCM-BIND Versus CCM-MIC 5.2. CCM-BIND Versus CCM-MIC
The first time a CCM context is needed between an principal on the 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 initiator and a principal on the target, the initiator has no choice
but to create an underlying mechanism context via a CCM-BIND context but to create an underlying mechanism context via a CCM-BIND context
token exchange. Once that is done, subsequent CCM contexts between token exchange. Once that is done, subsequent CCM contexts between
the initiator and target can be created via CCM-MIC. CCM-MIC context the initiator and target can be created via CCM-MIC. CCM-MIC context
establishment is better because no more than one round trip is establishment is better because no more than one round trip is
necessary to establish a CCM context, and because the overhead of the necessary to establish a CCM context, and because the overhead of the
establishing a real, underlying mechanism context is avoided. establishing a real, underlying mechanism context is avoided.
9.3. Initiating CCM-MIC Contexts 5.3. Initiating CCM-MIC Contexts
The key issue is how to associate an CCM-BIND established security The issue is how to associate an CCM-BIND established security
context with a new CCM-MIC context, There no existing interfaces context with a new CCM-MIC context, There are no existing interfaces
defined in the GSS-API for associating one GSS context with another. defined in the GSS-API for associating one GSS context with another.
This then is the key issue for implementations of CCM-MIC. This then is the key issue for implementations of CCM-MIC.
We will assume that GSS-API implementation is in the C programming We will assume that GSS-API implementation is in the C programming
language and therefore the GSS-API C bindings [RFC2744] are being language and therefore the GSS-API C bindings [RFC2744] are being
used. The CCM mechanism implementation will have a table that maps 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 ccmMicCcmBindCtxHandle values to gss_ctx_id_t values (see section
[RFC2744]). The latter are GSS-API context handles as returned by 5.19 of [RFC2744]). The latter are GSS-API context handles as
gss_init_sec_context(). The former are the context handles as returned by gss_init_sec_context(). In addition, each CCM context has
returned in a response token from the CCM target. In addition, each a reference to its underlying mechanism context.
CCM context has a reference to its underlying mechanism context.
Let us suppose the application decides it will use CCM-MIC. CCM-MIC 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. has a well known mechanism OID which the application can check for.
The point where the initiator calls GSS_Init_sec_context(), is a The point where the initiator calls GSS_Init_sec_context(), is a
logical place to associate an existing CCM-BIND context with a new logical place to associate an existing CCM-BIND context with a new
CCM-MIC context. Here is where special CCM handling is necessary in CCM-MIC context. Here is where special CCM handling is necessary in
order to associate a security context with a CCM context. We discuss order to associate a security context with a CCM context. We discuss
several approaches. several approaches.
1. The first approach is for the CCM-MIC's GSS_Init_sec_context() 1. The first approach is for the CCM-MIC's GSS_Init_sec_context()
entry point to pass as the claimant_cred_handle the entry point to pass as the claimant_cred_handle the
output_context_handle as returned by GSS_Init_sec_context() for output_context_handle as returned by GSS_Init_sec_context() for
a previously created CCM-BIND context. Such an approach may a previously established CCM-BIND context. Such an approach may
work well with applications that normally pass work well with applications that normally pass
GSS_C_NO_CREDENTIAL as the claimant_cred_handle. GSS_C_NO_CREDENTIAL as the claimant_cred_handle.
2. The second approach derives from the observation that normally, 2. The second approach derives from the observation that normally,
the first time GSS_Init_sec_context() is called, the input_token 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) 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 is also NULL. The input_token is supposed to be the token
received from the target's context acceptance routine, which has received from the target's context acceptance routine, which has
the XDR type CCM_MIC_resp_t. Overloading the input_token is one the XDR type ccmMicResp. Overloading the input_token is one
way. By passing in a non-null input_token, and a NULL pointer way. By passing in a non-null input_token, and a NULL pointer
to the context_handle (using the C bindings calling conventions to the context_handle (using the C bindings calling conventions
for gss_init_sec_context()), this will tell the CCM-MIC for gss_init_sec_context()), this will tell the CCM-MIC
initiator that input_token containing information to to initiator that input_token containing information to to
associate a new CCM-MIC context with an existing CCM-BIND associate a new CCM-MIC context with an existing CCM-BIND
context. In the C programming language, we could thus have have context. In the C programming language, we could thus have have
input_token containing: input_token containing:
typedef struct { typedef struct {
gss_ctx_id_t context_ptr; gss_ctx_id_t ccmMicCcmBindCtxPtr;
} CCM_MIC_initiator_bootstrap_t; } ccmMicCcmBindBootStrap;
The CCM entry point for creating contexts on the initiator side The CCM entry point for creating contexts on the initiator side
would, if being called for the first time (*context_handle is would, if being called for the first time (*context_handle is
NULL), interpret the presence of the input token with an invalid NULL), interpret the presence of the input token with an invalid
status as the CCM_MIC_initiator_bootstrap_t. It would use status as the ccmMicCcmBindBootStrap. It would use
context_ptr to lookup the corresponding gss_targ_ctx in the ccmMicCcmBindCtxPtr to lookup the corresponding
aforementioned gss_ctx_id_t to gss_targ_ctx mapping table. It ccmMicCcmBindCtxHandle in the aforementioned gss_ctx_id_t to
would then proceed to generate an output token encoded as XDR ccmMicCcmBindCtxHandle mapping table. It would then proceed to
type CCM_MIC_init_t, described in the section entitled "Initial generate an output token encoded as XDR type CCM_MIC_init_t,
Context Token for CCM-MIC". described in the section entitled "Initial Context Token for
CCM-MIC".
Regardless of the approach taken, the first time GSS_Init_sec_context Regardless of the approach taken, the first time GSS_Init_sec_context
is called, assuming success, it will return GSS_S_CONTINUE_NEEDED, is called, assuming success, it will return GSS_S_CONTINUE_NEEDED,
because it will need to process the token returned by the target. because it will need to process the token returned by the target.
The second time it is called, assuming success, it will return The second time it is called, assuming success, it will return
GSS_S_COMPLETE. GSS_S_COMPLETE.
9.4. Accepting CCM-MIC Contexts 5.4. Accepting CCM-MIC Contexts
The CCM-MIC target receives an opaque gss_targ_ctx value as part of The CCM-MIC target receives an opaque ccmMicCcmBindCtxHandle value as
the mechanism dependent part of the initial context token. part of the mechanism dependent part of the initial context token.
Originally, this opaque handle came from the target as a result of Originally, this opaque handle came from the target as a result of
previously creating a context via a CCM-BIND context exchange. If previously creating a context via a CCM-BIND context exchange. If
the opaque handle is still valid, then the target can easily the opaque handle is still valid, then the target can easily
determine the original CCM-BIND context, and from that, the CCM-BIND determine the original CCM-BIND context, and from that, the CCM-BIND
mechanism's context. With the underlying context, GSS_VerifyMIC() mechanism's context. With the underlying context, GSS_VerifyMIC()
can be invoked (with a qop_req of CCM_REAL_QOP (1)) to verify the 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 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 generate the ccmMicRespInitTkn field of the output token. By
the ctx_sh_number in the initiator's token with highest value comparing the ctxMicIndex in the initiator's token with highest value
recorded by the target, the target takes care to ensure that recorded by the target, the target takes care to ensure that
initiator has not replayed a short token. initiator has not replayed an initial CCM-MIC context token.
9.5. Non-Token Generating GSS-API Routines 5.5. Non-Token Generating GSS-API Routines
Since the CCM module will record the underlying mechanism's context Since the CCM module will record the underlying mechanism's context
pointer in its internal data structures, this provides a simple 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 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 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 for such an operation, it simply re-invokes the GSS-API call, but on
the recorded underlying context. the recorded underlying context.
9.6. CCM-MIC and GSS_Delete_sec_context() 5.6. CCM-MIC and GSS_Delete_sec_context()
The CCM-MIC entry point for GSS_Delete_sec_context() should not call The CCM-MIC entry point for GSS_Delete_sec_context() should not call
the underlying mechanism's GSS_Delete_sec_context() routine. If it the underlying mechanism's GSS_Delete_sec_context() routine. If it
did, this would effectively delete all CCM-MIC context's associating did, this would effectively delete all CCM-MIC context's associating
with the same underlying mechanism. with the same underlying mechanism.
9.7. GSS Status Codes 5.7. GSS Status Codes
9.7.1. Status Codes for CCM-BIND 5.7.1. Status Codes for CCM-BIND
CCM-BIND mechanisms define no minor status codes. If the underlying CCM-BIND mechanisms define no minor status codes. If the underlying
mechanism is not available, then a CCM-BIND mechanism will return mechanism is not available, then a CCM-BIND mechanism will return
GSS_S_BAD_MECH and minor status of zero. Otherwise, it will return GSS_S_BAD_MECH and minor status of zero. Otherwise, it will return
whatever major and minor status codes the underlying mechanism whatever major and minor status codes the underlying mechanism
returns. returns.
9.7.2. Status Codes for CCM-MIC 5.7.2. Status Codes for CCM-MIC
Generally, major and minor status codes for will be whatever major Generally, major and minor status codes for will be whatever major
and minor status codes the underlying CCM-BIND mechanism returns. and minor status codes the underlying CCM-BIND mechanism returns.
However, for GSS_Init_sec_context() and GSS_Accept_sec_context(), However, for GSS_Init_sec_context() and GSS_Accept_sec_context(),
this is not the case because the those operations are invoking this is not the case because the those operations are invoking
routines (GSS_Wrap() and GSS_Unwrap()) that have major statuses that routines (GSS_Wrap() and GSS_Unwrap()) that have major statuses that
are not subsets of the legal status returns from are not subsets of the legal status returns from
GSS_Init_sec_context() and GSS_Accept_sec_context(). Moreover, in GSS_Init_sec_context() and GSS_Accept_sec_context(). Moreover, in
some cases for GSS_Init_sec_context(), the minor and major status are 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 driven from the target, and the target's codes will not always be
among the legal set for GSS_Init_sec_context(). among the legal set for GSS_Init_sec_context().
9.7.2.1. CCM-MIC: GSS_Accept_sec_context() status codes 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 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 set defined in the ccmMicStatus type. If GSS_Unwrap() reports a
major status failure, then the minor status will be major status failure, then the minor status will be
CCM_ERR_TKN_UNWRAP, and the reported major status will what CCM_ERR_TKN_UNWRAP, and the reported major status will what
GSS_Unwrap() reports, with exceptions as according to the following GSS_Unwrap() reports, with exceptions as according to the following
table: table:
major status code from GSS_Unwrap major status code reported major status code from GSS_Unwrap major status code reported
by GSS_Accept_sec_context by GSS_Accept_sec_context
to caller. to caller.
----------------------------------------------------------------- -----------------------------------------------------------------
GSS_S_BAD_SIG GSS_S_BAD_SIG GSS_S_BAD_SIG GSS_S_BAD_SIG
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
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GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN
GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN
If GSS_GetMIC() reports a major status failure, then the minor status 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 will be CCM_ERR_TKN_GET_MIC, and the reported major status will be
what GSS_GetMIC() reports, with exceptions as according to the what GSS_GetMIC() reports, with exceptions as according to the
following table: following table:
major status code from GSS_GetMIC major status code reported major status code from GSS_GetMIC major status code reported
by GSS_Accept_sec_context() by GSS_Accept_sec_context()
to caller. to caller.
------------------------------------------------------------------ ------------------------------------------------------------------
GSS_S_BAD_QOP GSS_S_FAILURE GSS_S_BAD_QOP GSS_S_FAILURE
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
The target will always report the actual GSS major and minor codes to The target will always report the actual GSS major and minor codes to
the initiator. The initiator will map the GSS major code as the initiator. The initiator will map the GSS major code as
described in the next subsection. described in the next subsection.
9.7.2.2. CCM-MIC: GSS_Init_sec_context() status codes 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 The minor status code for GSS_Init_sec_context is always from the set
defined in the CCM_MIC_status_t type. defined in the ccmMicStatus type.
If the minor status code came from the target, then that will always 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 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: from the target are to be mapped to the major status code as follows:
minor status code major status code minor status code major status code
from target reported to caller of from target reported to caller of
GSS_Init_sec_context() GSS_Init_sec_context()
---------------------------------------------------- ----------------------------------------------------
CCM_OK GSS_S_COMPLETE CCM_OK GSS_S_COMPLETE
CCM_ERR_HANDLE_MALFORMED GSS_S_DEFECTIVE_TOKEN CCM_ERR_HANDLE_MALFORMED GSS_S_DEFECTIVE_TOKEN
skipping to change at page 20, line 29 skipping to change at page 19, line 21
GSS_VerifyMIC() reports, with exceptions as according to the GSS_VerifyMIC() reports, with exceptions as according to the
following table: following table:
major status code from GSS_VerifyMIC major status code reported major status code from GSS_VerifyMIC major status code reported
by GSS_Init_sec_context() by GSS_Init_sec_context()
to caller to caller
--------------------------------------------------------------- ---------------------------------------------------------------
GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN GSS_S_CONTEXT_EXPIRED GSS_S_DEFECTIVE_TOKEN
GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN GSS_S_GAP_TOKEN GSS_S_DEFECTIVE_TOKEN
GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN GSS_S_UNSEQ_TOKEN GSS_S_DUPLICATE_TOKEN
9.8. Channel Bindings on the Target 6. Advice for NFSv4 Implementors
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.
10. Advice for NFSv4 Implementors
The NFSv4.0 specification does not mandate CCM, so clients and The NFSv4.0 specification does not mandate CCM, so client and server
servers should not insist on its use. When a server wants a client implementations should not insist on its use. When a server wants a
to try to use CCM, it can return a NFS4ERR_WRONGSEC error to the client to try to use CCM, it can return a NFS4ERR_WRONGSEC error to
client. The client will then follow up with a SECINFO request. The the client. The client will then follow up with a SECINFO request.
response to the SECINFO request should list first the CCM-BIND The response to the SECINFO request should list first the CCM-BIND
mechanisms it supports, second the CCM-MIC mechanism (if supported), mechanisms it supports, second the CCM-MIC mechanism (if supported),
and finally, the conventional security flavors the server will accept and finally, the conventional security flavors the server will accept
for access to file object. If the client supports CCM, it will use for access to file object. If the client supports CCM, it will use
it. Otherwise, it will have to stick with a conventional flavor. 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 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 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 sure that a CCM-MIC context is authorized access an object. For
example suppose /export is exported such that SPKM-3 is the example suppose /export is exported such that SPKM-3 is the
authorized underlying mechanism, and CCM-NULL + SPKM-3 and CCM-MIC authorized underlying mechanism, and CCM-NULL + SPKM-3 and CCM-MIC
are similarly authorized to access /export. Suppose CCM-NULL is are similarly authorized to access /export. Suppose CCM-NULL is
created over a Kerberos V5 context, and then CCM-MIC is used to 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 derived a context from the CCM-NULL context. If the NFS server
simply records that the OID of CCM-MIC is authorized to access simply records that the OID of CCM-MIC is authorized to access
/export, then Kerberos V5 authenticated users will be mistakenly /export, then Kerberos V5 authenticated users will be mistakenly
allowed access. Instead, the server needs to examine what context allowed access. Instead, the server needs to examine what context
the CCM-MIC context is associated with, and check that context's OID the CCM-MIC context is associated with, and check that context's OID
against the authorized list of OIDs for /export. against the authorized list of OIDs for /export.
11. Man in the Middle Attacks without CCM-KEY 7. Security Considerations
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
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 There are many considerations for the use CCM, since it is reducing
security at one protocol layer in trade for equivalent security at security at one protocol layer in trade for equivalent security at
another layer. In this discussion, we will assume that cryptography another layer. In this discussion, we will assume that cryptography
is being used in the application and lower protocol layers. is being used in the application and lower protocol layers.
* CCM should not be used whenever the combined key * CCM should not be used whenever the combined key
strength/algorithm strength of the lower protocol layer securing strength/algorithm strength of the lower protocol layer securing
the connection is weaker than what the underlying GSS context the connection is weaker than what the underlying GSS context
can provide. can provide.
skipping to change at page 23, line 14 skipping to change at page 20, line 41
all users of the secure channel are compromised. all users of the secure channel are compromised.
* CCM contexts created during one session or transport connection * CCM contexts created during one session or transport connection
SHOULD not be used for subsequent sessions or transport SHOULD not be used for subsequent sessions or transport
connections. In other words, full initiator to target connections. In other words, full initiator to target
authentication SHOULD occur each time a session or transport authentication SHOULD occur each time a session or transport
connection is established. Otherwise, there is nothing connection is established. Otherwise, there is nothing
preventing an attacker from using a CCM context from one preventing an attacker from using a CCM context from one
authenticated session or connection to trivially establish authenticated session or connection to trivially establish
another, unauthenticated session or connection. For efficiency, another, unauthenticated session or connection. For efficiency,
a CCM-BIND context from a previous session MAY be used to a CCM-BIND context from a previous session or connection MAY be
establish a CCM-MIC context. used to establish a CCM-MIC context.
If the application protocol using CCM has no concept of a If the application protocol using CCM has no concept of a
session and does not use a connection oriented transport, then session and does not use a connection oriented transport, then
there is no sequence of state transitions that tie the CCM there is no sequence of state transitions that tie the CCM
context creation steps with the subsequent message traffic of context creation steps with the subsequent message traffic of
the application protocol. Thus it can be hard to assert that the application protocol. Thus it can be hard to assert that
the subsequent message traffic is truly originated by the CCM the subsequent message traffic is truly originated by the CCM
initiator's principal. For this reason, CCM SHOULD NOT be used initiator's principal. For this reason, CCM SHOULD NOT be used
with applications that do not have sessions or do not use with applications that do not have sessions or do not use
connection oriented transports. connection oriented transports.
skipping to change at page 23, line 38 skipping to change at page 21, line 16
initiator to the target. It is permissible for the user to initiator to the target. It is permissible for the user to
configure the underlying secure channel to not be end to end, configure the underlying secure channel to not be end to end,
but this should only be done if user has confidence in the but this should only be done if user has confidence in the
intermediate end points. For example, suppose the application intermediate end points. For example, suppose the application
is being used behind a firewall that performs network address is being used behind a firewall that performs network address
translation. It is possible to have an IPsec secure channel translation. It is possible to have an IPsec secure channel
from the initiator to the firewall, and a second 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 from the firewall to the target, but not from the initiator to
the target. So, if the firewall is compromised by an attacker the target. So, if the firewall is compromised by an attacker
in the middle, the use of CCM to avoid per message in the middle, the use of CCM to avoid per message
authentication is useless. Furthermore, without channel authentication is useless. Of course, if the initiator's node
bindings mandated by CCM-KEY, it is not possible for the created a IP-layer tunnel between it and the target, end to end
initiator and target to enforce end to end channel security. Of channel security would be achieved.
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 * It has been stated that it is not uncommon to find IPsec
deployments where multiple nodes share common private keys deployments where multiple nodes share common private keys
[Black]. The use of CCM is discouraged in such environments, [Black]. The use of CCM is discouraged in such environments,
since the compromise of one node compromises all the other nodes since the compromise of one node compromises all the other nodes
sharing the same private key. sharing the same private key.
* Applications using CCM MUST ensure that the binding between the * Applications using CCM MUST ensure that the binding between the
CCM context and the secure channel is legitimate for each CCM context and the secure channel is legitimate for each
message that references the CCM context. In other words, the message that references the CCM context. In other words, the
referenced CCM context in a message MUST be established in the referenced CCM context in a message MUST be established in the
same secure channel as the message. The use of CCM-KEY enforces same secure channel as the message.
this binding.
* When the same secure channel is multiplexing traffic for * When the same secure channel is multiplexing traffic for
multiple users, the initiator has to ensure the CCM context is multiple users, the initiator has to ensure the CCM context is
only accessible to the initiator principal that has established only accessible to the initiator principal that has established
it in the first place. One possible way to ensure that is by it in the first place. One possible way to ensure that is by
placing CCM contexts in the privileged address space offering placing CCM contexts in the privileged address space offering
only controlled indexed access. only controlled indexed access.
* CCM does not unnecessarily inflate the scope of the trust * CCM does not unnecessarily inflate the scope of the trust
domain, as does for example AUTH_SYS [RFC1831] over IPSec. By domain, as does for example AUTH_SYS [RFC1831] over IPSec. By
skipping to change at page 24, line 31 skipping to change at page 21, line 53
not extend to the client. not extend to the client.
* Both the traditional mechanisms and CCM rely on the security of * Both the traditional mechanisms and CCM rely on the security of
the client to protect locally logged on users. Compromise of the client to protect locally logged on users. Compromise of
the client impacts all users on the same client. CCM does not the client impacts all users on the same client. CCM does not
make the problem worse. make the problem worse.
* The CCM context MUST be established over the same secure channel * The CCM context MUST be established over the same secure channel
that the subsequent message traffic will be using. This way, that the subsequent message traffic will be using. This way,
the binding between the initial authentication and the the binding between the initial authentication and the
subsequent traffic is ensured. Again, the use of CCM-KEY is one subsequent traffic is ensured.
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- * If an application is using IPsec and CCM-NULL then then the site
ADDR's bindings are simply public network addresses. If the where the application is deployed should configure the IPsec SPD
secure channel is IPsec, and non-anonymous certificates are used to carefully limit the ports and nodes that are allowed create
with IKE, then a MITM cannot spoof the target's and initiator's security associations to application targets.
IP addresses, because the attacker will presumably be unable to
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- * CCM contexts should not be used forever without re-
authenticating periodically via the underlying mechanism. One authenticating periodically via the underlying mechanism. One
rational approach is for the CCM context to persist no longer rational approach is for the CCM context to persist no longer
than the underlying mechanism context. Implementing this via than the underlying mechanism context. Implementing this via
the GSS-API is simple. Applications can periodically invoke the GSS-API is simple. Applications can periodically invoke
gss_context_time() to find out how long the context will be gss_context_time() to find out how long the context will be
valid. Moreover, CCM can enforce this by invoking valid. Moreover, CCM can enforce this by invoking
gss_context_time() and the system time of day API to get an gss_context_time() and the system time of day API to get an
expiration date when the CCM mechanism is established. Each expiration date when the CCM mechanism is established. Each
subsequent call can check the time of day against the subsequent call can check the time of day against the
expiration, and if expired, return GSS_S_CONTEXT_EXPIRED. expiration, and if expired, return GSS_S_CONTEXT_EXPIRED.
13. IANA Considerations 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
* 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
};
/*
* 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- 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 MIC mechanism OID must be assigned and registered by IANA. Please
look for TBD1 in this document and notify the RFC Editor what value look for TBD1 in this document and notify the RFC Editor what value
you have assigned. you have assigned.
XXX Note 1 to RFC Editor: When IANA has made the OID assignments, XXX Note 1 to RFC Editor: When IANA has made the OID assignments,
please do the following: please do the following:
* Delete the "XXX Note 1 to RFC Editor: ..." paragraph. * Delete the "XXX Note 1 to RFC Editor: ..." paragraph.
* Replace occurrences of TBD1 with the value assigned by IANA. * Replace occurrences of TBD1 with the value assigned by IANA.
* Replace the "XXX Note 1 to IANA: ..." paragraph with: * Replace the "XXX Note 1 to IANA: ..." paragraph with:
OIDs for the CCM-BIND mechanism prefix, and for the CCM-MIC OIDs for the CCM-BIND mechanism prefix, and for the CCM-MIC
mechanism have been assigned by, and registered with IANA, mechanism have been assigned by, and registered with IANA,
with this document as the reference. with this document as the reference.
XXX Note 2 to IANA: Please assign RPC flavor numbers for values XXX Note 2 to IANA: Please assign RPC flavor numbers for values
currently place held in this document as TBD2 through TBD10. Also currently place held in this document as TBD2 through TBD5. Also
please establish the registry that RFC2623 mandates. please establish the registry that RFC2623 mandates.
XXX Note 2 to RFC Editor: When IANA has made the RPC flavor number XXX Note 2 to RFC Editor: When IANA has made the RPC flavor number
assignments, please do the following: assignments, please do the following:
* Delete the "XXX Note 2 to RFC Editor: ..." paragraph. * Delete the "XXX Note 2 to RFC Editor: ..." paragraph.
* Replace occurrences of TBD2 through and including TBD10 withe * Replace occurrences of TBD2 through and including TBD5 withe
flavor number assignments from IANA. flavor number assignments from IANA.
Section 6, "IANA Considerations" of [RFC2623] established a registry Section 6, "IANA Considerations" of [RFC2623] established a registry
for mapping GSS mechanism OIDs to RPC pseudo flavor numbers. This for mapping GSS mechanism OIDs to RPC pseudo flavor numbers. This
registry was augmented in the NFSv4 specification [RFC3530] with registry was augmented in the NFSv4 specification [RFC3530] with
several more entries. This document adds the following entries to several more entries. This document adds the following entries to
the registry: the registry:
1 == number of pseudo flavor 1 == number of pseudo flavor
2 == name of pseudo flavor 2 == name of pseudo flavor
skipping to change at page 26, line 24 skipping to change at page 25, line 29
4 == quality of protection 4 == quality of protection
5 == RPCSEC_GSS service 5 == RPCSEC_GSS service
1 2 3 4 5 1 2 3 4 5
-------------------------------------------------------------- --------------------------------------------------------------
TBD2 ccm-mic 1.3.6.1.5.5.TBD1.2 0 rpc_gss_svc_none 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 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 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 TBD4 ccm-null-spkm3 1.3.6.1.5.5.TBD1.1.1. 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 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 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 1.3.6.1.5.5.1.3
14. Acknowledgements 10. Acknowledgements
Dave Noveck, for the observation that NFS version 4 servers could Dave Noveck, for the observation that NFS version 4 servers could
downgrade from integrity service to plain authentication service if downgrade from integrity service to plain authentication service if
IPsec was enabled. David Black, Peng Dai, Sam Hartman, Martin Rex, IPsec was enabled. David Black, Peng Dai, Sam Hartman, Martin Rex,
and Julian Satran, for their critical comments. Much of the text for and Julian Satran, for their critical comments. Much of the text for
the "Security Considerations" section comes directly from David and the "Security Considerations" section comes directly from David and
Peng. Peng.
15. Normative References 11. Normative References
[RFC1832] [RFC1832]
R. Srinivasan, RFC1832, "XDR: External Data Representation R. Srinivasan, RFC1832, "XDR: External Data Representation
Standard", August, 1995. Standard", August, 1995.
[RFC2025] [RFC2025]
C. Adams, RFC2025: "The Simple Public-Key GSS-API Mechanism C. Adams, RFC2025: "The Simple Public-Key GSS-API Mechanism
(SPKM)," October 1996, Status: Standards Track. (SPKM)," October 1996, Status: Standards Track.
[RFC2119] [RFC2119]
skipping to change at page 27, line 46 skipping to change at page 26, line 37
bindings", January, 2000. bindings", January, 2000.
[RFC2847] [RFC2847]
M. Eisler, RFC2847: "LIPKEY - A Low Infrastructure Public Key M. Eisler, RFC2847: "LIPKEY - A Low Infrastructure Public Key
Mechanism Using SPKM," June 2000, Status: Standards Track. Mechanism Using SPKM," June 2000, Status: Standards Track.
[FIPS]U.S. Department of Commerce / National Institute of Standards [FIPS]U.S. Department of Commerce / National Institute of Standards
and Technology, FIPS PUB 180-1, "Secure Hash Standard", May 11, and Technology, FIPS PUB 180-1, "Secure Hash Standard", May 11,
1993. 1993.
[IKEv2] 12. Informative References
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
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] [RFC1831]
R. Srinivasan, RFC1831, "RPC: Remote Procedure Call Protocol R. Srinivasan, RFC1831, "RPC: Remote Procedure Call Protocol
Specification Version 2", August, 1995. Specification Version 2", August, 1995.
[RFC1964] [RFC1964]
J. Linn, RFC1964, "The Kerberos Version 5 GSS-API Mechanism", J. Linn, RFC1964, "The Kerberos Version 5 GSS-API Mechanism",
June 1996. June 1996.
[RFC2203] [RFC2203]
skipping to change at page 29, line 8 skipping to change at page 27, line 26
[DAFS] [DAFS]
Mark Wittle (Editor), "DAFS Direct Access File System Protocol, Mark Wittle (Editor), "DAFS Direct Access File System Protocol,
Version: 1.00", September 1, 2001. Version: 1.00", September 1, 2001.
[Kasslin] [Kasslin]
Kasslin, K. "Attacks on Kerberos V in a Windows 2000 Kasslin, K. "Attacks on Kerberos V in a Windows 2000
Environment", 2003. Environment", 2003.
http://www.hut.fi/~autikkan/hakkeri/docs/phase1/pdf/ http://www.hut.fi/~autikkan/hakkeri/docs/phase1/pdf/
LATEST_final_report.pdf LATEST_final_report.pdf
17. Authors' Addresses 13. Authors' Addresses
Mike Eisler Mike Eisler
5765 Chase Point Circle 5765 Chase Point Circle
Colorado Springs, CO 80919 Colorado Springs, CO 80919
USA USA
Phone: 719-599-9026 Phone: 719-599-9026
EMail: mike@eisler.com EMail: mike@eisler.com
Nicolas Williams Nicolas Williams
Sun Microsystems, Inc. Sun Microsystems, Inc.
5300 Riata Trace CT 5300 Riata Trace CT
Austin, TX 78727 Austin, TX 78727
USA USA
EMail: nicolas.williams@sun.com EMail: nicolas.williams@sun.com
18. IPR Notices 14. IPR Notices
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of claims of rights made available for publication and any assurances of
skipping to change at page 29, line 48 skipping to change at page 28, line 18
obtain a general license or permission for the use of such obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat. be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF Executive
Director. Director.
19. Copyright Notice 15. 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
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 Copyright (C) The Internet Society (2004). This document is subject
revoked by the Internet Society or its successors or assigns. 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 is provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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