x
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@12708 ec53bebd-3082-4978-b11e-865c3cabbd6b
This commit is contained in:
816
doc/standardisation/draft-ietf-krb-wg-gssapi-cfx-01.txt
Normal file
816
doc/standardisation/draft-ietf-krb-wg-gssapi-cfx-01.txt
Normal file
@@ -0,0 +1,816 @@
|
|||||||
|
|
||||||
|
|
||||||
|
<Kerberos Working Group> Larry Zhu
|
||||||
|
Internet Draft Karthik Jaganathan
|
||||||
|
Updates: 1964 Microsoft
|
||||||
|
Category: Standards Track Sam Hartman
|
||||||
|
draft-ietf-krb-wg-gssapi-cfx-01.txt MIT
|
||||||
|
August 29, 2003
|
||||||
|
Expires: February 29, 2004
|
||||||
|
|
||||||
|
The Kerberos Version 5 GSS-API Mechanism: Version 2
|
||||||
|
|
||||||
|
Status of this Memo
|
||||||
|
|
||||||
|
This document is an Internet-Draft and is in full conformance with
|
||||||
|
all provisions of Section 10 of [RFC-2026].
|
||||||
|
|
||||||
|
Internet-Drafts are working documents of the Internet Engineering
|
||||||
|
Task Force (IETF), its areas, and its working groups. Note that
|
||||||
|
other groups may also distribute working documents as Internet-
|
||||||
|
Drafts. Internet-Drafts are draft documents valid for a maximum of
|
||||||
|
six months and may be updated, replaced, or obsoleted by other
|
||||||
|
documents at any time. It is inappropriate to use Internet- Drafts
|
||||||
|
as reference material or to cite them other than as "work in
|
||||||
|
progress."
|
||||||
|
The list of current Internet-Drafts can be accessed at
|
||||||
|
http://www.ietf.org/ietf/1id-abstracts.txt
|
||||||
|
The list of Internet-Draft Shadow Directories can be accessed at
|
||||||
|
http://www.ietf.org/shadow.html.
|
||||||
|
|
||||||
|
|
||||||
|
1. Abstract
|
||||||
|
|
||||||
|
[RFC-1964] defines protocols, procedures, and conventions to be
|
||||||
|
employed by peers implementing the Generic Security Service
|
||||||
|
Application Program Interface (as specified in [RFC-2743]) when
|
||||||
|
using the Kerberos Version 5 mechanism (as specified in [KRBCLAR]).
|
||||||
|
|
||||||
|
This memo obsoletes [RFC-1964] and proposes changes in response to
|
||||||
|
recent developments such as the introduction of Kerberos crypto
|
||||||
|
framework. It is intended that this memo or a subsequent version
|
||||||
|
will become the Kerberos Version 5 GSS-API mechanism specification
|
||||||
|
on the standards track.
|
||||||
|
|
||||||
|
2. Conventions used in this document
|
||||||
|
|
||||||
|
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
|
||||||
|
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
|
||||||
|
document are to be interpreted as described in [RFC-2119].
|
||||||
|
|
||||||
|
3. Introduction
|
||||||
|
|
||||||
|
[KCRYPTO] defines a generic framework for describing encryption and
|
||||||
|
checksum types to be used with the Kerberos protocol and associated
|
||||||
|
protocols.
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Standards Trace - February 16, 2003 1
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
[RFC-1964] describes the GSSAPI mechanism for Kerberos V5. It
|
||||||
|
defines the format of context initiation, per-message and context
|
||||||
|
deletion tokens and uses algorithm identifiers for each cryptosystem
|
||||||
|
in per message and context deletion tokens.
|
||||||
|
|
||||||
|
The approach taken in this document obviates the need for algorithm
|
||||||
|
identifiers. This is accomplished by using the same encryption and
|
||||||
|
checksum algorithms specified by the crypto profile [KCRYPTO] for
|
||||||
|
the session key or subkey that is created during context
|
||||||
|
negotiation. Message layouts of the per-message and context
|
||||||
|
deletion tokens are therefore revised to remove algorithm indicators
|
||||||
|
and also to add extra information to support the generic crypto
|
||||||
|
framework [KCRYPTO].
|
||||||
|
|
||||||
|
Tokens transferred between GSS-API peers for security context
|
||||||
|
initiation are also described in this document. The data elements
|
||||||
|
exchanged between a GSS-API endpoint implementation and the Kerberos
|
||||||
|
KDC are not specific to GSS-API usage and are therefore defined
|
||||||
|
within [KRBCLAR] rather than within this specification.
|
||||||
|
|
||||||
|
The new token formats specified in this memo MUST be used with all
|
||||||
|
"newer" encryption types [KRBCLAR] and MAY be used with "older"
|
||||||
|
encryption types, provided that the initiator and acceptor know,
|
||||||
|
from the context establishment, that they can both process these new
|
||||||
|
token formats.
|
||||||
|
|
||||||
|
"Newer" encryption types are those which have been specified along
|
||||||
|
with or since the new Kerberos cryptosystem specification [KCRYPTO]
|
||||||
|
[KRBCLAR].
|
||||||
|
|
||||||
|
Note that in this document, "AES" is used for brevity to refer
|
||||||
|
loosely to either aes128-cts-hmac-sha1-96 or aes256-cts-hmac-sha1-96
|
||||||
|
as defined in [AES-KRB5]. AES is used as an example of the new
|
||||||
|
method defined in this document.
|
||||||
|
|
||||||
|
4. Key Derivation for Per-Message and Context Deletion Tokens
|
||||||
|
|
||||||
|
To limit the exposure of a given key, [KCRYPTO] adopted "one-way"
|
||||||
|
"entropy-preserving" derived keys, for different purposes or key
|
||||||
|
usages, from a base key or protocol key. This document defines four
|
||||||
|
key usage values below for signing and sealing messages:
|
||||||
|
|
||||||
|
Name value
|
||||||
|
-------------------------------------
|
||||||
|
KG-USAGE-ACCEPTOR-SEAL 22
|
||||||
|
KG-USAGE-ACCEPTOR-SIGN 23
|
||||||
|
KG-USAGE-INITIATOR-SEAL 24
|
||||||
|
KG-USAGE-INITIATOR-SIGN 25
|
||||||
|
|
||||||
|
When the sender is the context acceptor, KG-USAGE-ACCEPTOR-SIGN is
|
||||||
|
used as the usage number in the key derivation function for deriving
|
||||||
|
keys to be used in MIC and context deletion tokens, and KG-USAGE-
|
||||||
|
ACCEPTOR-SEAL is used for Wrap tokens; similarly when the sender is
|
||||||
|
the context initiator, KG-USAGE-INITIATOR-SIGN is used as the usage
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 2
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
number in the key derivation function for MIC and context deletion
|
||||||
|
tokens, KG-USAGE-INITIATOR-SEAL is used for Wrap Tokens. Even if
|
||||||
|
the Wrap token does not provide for confidentiality the same usage
|
||||||
|
values specified above are used.
|
||||||
|
|
||||||
|
5. Quality of Protection
|
||||||
|
|
||||||
|
The GSSAPI specification [RFC-2743] provides for Quality of
|
||||||
|
Protection (QOP) values that can be used by the application to
|
||||||
|
request a certain type of encryption or signing. A zero QOP value
|
||||||
|
is used to indicate the "default" protection; applications which use
|
||||||
|
the default QOP are not guaranteed to be portable across
|
||||||
|
implementations or even inter-operate with different deployment
|
||||||
|
configurations of the same implementation. Using an algorithm that
|
||||||
|
is different from the one for which the key is defined may not be
|
||||||
|
appropriate. Therefore, when the new method in this document is
|
||||||
|
used, the QOP value is ignored.
|
||||||
|
|
||||||
|
The encryption and checksum algorithms in per-message and context
|
||||||
|
deletion tokens are now implicitly defined by the algorithms
|
||||||
|
associated with the session key or subkey. Algorithms identifiers
|
||||||
|
as described in [RFC-1964] are therefore no longer needed and
|
||||||
|
removed from the new token headers.
|
||||||
|
|
||||||
|
6. Token Framing
|
||||||
|
|
||||||
|
Per [RFC-2743], all tokens emitted by the Kerberos V5 GSS-API
|
||||||
|
mechanism will have the framing shown below:
|
||||||
|
|
||||||
|
GSS-API DEFINITIONS ::=
|
||||||
|
|
||||||
|
BEGIN
|
||||||
|
|
||||||
|
MechType ::= OBJECT IDENTIFIER
|
||||||
|
-- representing Kerberos V5 mechanism
|
||||||
|
|
||||||
|
GSSAPI-Token ::=
|
||||||
|
-- option indication (delegation, etc.) indicated within
|
||||||
|
-- mechanism-specific token
|
||||||
|
[APPLICATION 0] IMPLICIT SEQUENCE {
|
||||||
|
thisMech MechType,
|
||||||
|
innerToken ANY DEFINED BY thisMech
|
||||||
|
-- contents mechanism-specific
|
||||||
|
-- ASN.1 structure not required
|
||||||
|
}
|
||||||
|
END
|
||||||
|
|
||||||
|
The innerToken field always starts with a two byte token-identifier
|
||||||
|
(TOK_ID). Here are the TOK_ID values:
|
||||||
|
|
||||||
|
Token TOK_ID Value in hex
|
||||||
|
-------------------------------------------
|
||||||
|
KRB_AP_REQUEST 01 00
|
||||||
|
KRB_AP_REQPLY 02 00
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 3
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
KRB_ERROR 03 00
|
||||||
|
[RFC-1964] MIC 01 01
|
||||||
|
[RFC-1964] Wrap 01 02
|
||||||
|
[RFC-1964] context deletion 02 01
|
||||||
|
MIC 04 04
|
||||||
|
Wrap 04 05
|
||||||
|
context deletion 05 04
|
||||||
|
|
||||||
|
|
||||||
|
7. Context Initialization Tokens
|
||||||
|
|
||||||
|
For context initialization tokens, the body for the innerToken field
|
||||||
|
contains a Kerberos V5 message (KRB_AP_REQUEST, KRB_AP_REPLY, or
|
||||||
|
KRB_ERROR) as defined in [KRBCLAR].
|
||||||
|
|
||||||
|
7.1. Authenticator Checksum
|
||||||
|
|
||||||
|
The authenticator in the KRB_AP_REQ message MUST include the
|
||||||
|
optional sequence number and the checksum field. The checksum field
|
||||||
|
is used to convey service flags, channel binding, and optional
|
||||||
|
delegation information. It MUST have a type of 0x8003. The length
|
||||||
|
of the checksum MUST be 24 bytes when delegation is not used. When
|
||||||
|
delegation is used, a TGT with its FORWARDABLE flag set will be
|
||||||
|
transferred within the KRB_CRED [KRBCLAR] message.
|
||||||
|
|
||||||
|
The format of the authenticator checksum field is as follows.
|
||||||
|
|
||||||
|
Byte Name Description
|
||||||
|
-----------------------------------------------------------------
|
||||||
|
0..3 Lgth Number of bytes in Bnd field;
|
||||||
|
Currently contains hex 10 00 00 00
|
||||||
|
(16, represented in little-endian form)
|
||||||
|
4..19 Bnd MD5 hash of channel bindings, taken over all
|
||||||
|
non-null components of bindings, in order
|
||||||
|
of declaration. Integer fields within channel
|
||||||
|
bindings are represented in little-endian order
|
||||||
|
for the purposes of the MD5 calculation.
|
||||||
|
20..23 Flags Bit vector of context-establishment flags,
|
||||||
|
as defined next. The resulting bit vector is
|
||||||
|
encoded into bytes 20..23 in little-endian form.
|
||||||
|
24..25 DlgOpt The Delegation Option identifier (=1) [optional]
|
||||||
|
26..27 Dlgth The length of the Deleg field [optional]
|
||||||
|
28..n Deleg A KRB_CRED message (n = Dlgth + 29) [optional]
|
||||||
|
|
||||||
|
[we need to get input on how to allow additional data for
|
||||||
|
extensions. Nicolas will post some text for this. If that is the
|
||||||
|
case, do we need to change the checksum type?]
|
||||||
|
|
||||||
|
7.1.1. Flags Field
|
||||||
|
|
||||||
|
The checksum flags are used to convey service options or extension
|
||||||
|
negotiation information. The bits in the Flags field are allocated
|
||||||
|
as follows (Most significant bit is bit 0):
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 4
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
Bit Name Description
|
||||||
|
----------------------------------------------------
|
||||||
|
0..11 Mandatory Critical extension flags
|
||||||
|
12..15 Optional Non-critical extension flags
|
||||||
|
16..31 Standard Context establishment flags
|
||||||
|
|
||||||
|
An extension or context establishment flag can either be critical or
|
||||||
|
non-critical. When the context initiator desires a particular
|
||||||
|
extension or context establishment flag (either critical or non-
|
||||||
|
critical) it sets the appropriate checksum flag. The context
|
||||||
|
acceptor MUST ignore unsupported non-critical extensions or flags in
|
||||||
|
the initiator's context token (i.e., acceptors MUST NOT return an
|
||||||
|
error just because there were unsupported non-critical extensions or
|
||||||
|
flags in the initiator's token). The acceptor MUST return
|
||||||
|
GSS_S_UNAVAILABLE [RFC-2743] if there are unsupported critical
|
||||||
|
extensions or flags in the initiator's context token.
|
||||||
|
|
||||||
|
The following context establishment flags are defined in [RFC-2744]
|
||||||
|
|
||||||
|
Flag Name Value
|
||||||
|
---------------------------------
|
||||||
|
GSS_C_DELEG_FLAG 1
|
||||||
|
GSS_C_MUTUAL_FLAG 2
|
||||||
|
GSS_C_REPLAY_FLAG 4
|
||||||
|
GSS_C_SEQUENCE_FLAG 8
|
||||||
|
GSS_C_CONF_FLAG 16
|
||||||
|
GSS_C_INTEG_FLAG 32
|
||||||
|
GSS_C_ANON_FLAG 64
|
||||||
|
|
||||||
|
Context establishment flags are exposed to the calling application.
|
||||||
|
If the calling application desires a particular service option then
|
||||||
|
it requests that option via GSS_Init_sec_context(). An
|
||||||
|
implementation that supports a particular extension SHOULD then set
|
||||||
|
the appropriate flag in the checksum Flags field.
|
||||||
|
|
||||||
|
All existing context establishment flags are non-critical, and it is
|
||||||
|
possible that a new context establishment flag can be added as a
|
||||||
|
critical flag.
|
||||||
|
|
||||||
|
7.1.2. Channel Binding Information
|
||||||
|
|
||||||
|
In computing the contents of the "Bnd" field, the following detailed
|
||||||
|
points apply:
|
||||||
|
|
||||||
|
(1) Each integer field shall be formatted into four bytes, using
|
||||||
|
little-endian byte ordering, for purposes of MD5 hash computation.
|
||||||
|
|
||||||
|
(2) All input length fields within gss_buffer_desc [RFC-2744]
|
||||||
|
elements of a gss_channel_bindings_struct [RFC-2744], even those
|
||||||
|
which are zero-valued, shall be included in the hash calculation;
|
||||||
|
the value elements of gss_buffer_desc elements shall be
|
||||||
|
dereferenced, and the resulting data shall be included within the
|
||||||
|
hash computation, only for the case of gss_buffer_desc elements
|
||||||
|
having non-zero length specifiers.
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 5
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
(3) If the caller passes the value GSS_C_NO_BINDINGS instead of a
|
||||||
|
valid channel bindings structure, the Bnd field shall be set to 16
|
||||||
|
zero-valued bytes.
|
||||||
|
|
||||||
|
[Nicolas suggested that the only change that might be needed here
|
||||||
|
was the use of SHA1 instead of MD5]
|
||||||
|
|
||||||
|
8. Per-Message and Context Deletion Tokens
|
||||||
|
|
||||||
|
The new per-message and context deletion token formats defined in
|
||||||
|
this document are designed to accommodate the requirements of newer
|
||||||
|
crypto systems. The token layouts have also been designed to
|
||||||
|
facilitate scatter-gather and in-place encryption without incurring
|
||||||
|
significant performance penalties for implementations that do not
|
||||||
|
allow for either scatter-gather or in-place encryption.
|
||||||
|
|
||||||
|
The design along with the rationale behind it is discussed in detail
|
||||||
|
in the following sections.
|
||||||
|
|
||||||
|
8.1. Sequence Number and Direction Indicator
|
||||||
|
|
||||||
|
The sequence number for any per-message or context deletion token is
|
||||||
|
a 64 bit integer (expressed in big endian order). One separate flag
|
||||||
|
is used as the direction-indicator as described in section 8.2.
|
||||||
|
Both the sequence number and the direction-indicator are protected
|
||||||
|
by the encryption and checksum procedures as specified in section
|
||||||
|
8.4.
|
||||||
|
|
||||||
|
8.2. Flags Field
|
||||||
|
|
||||||
|
The Flags field is a one-byte bit vector used to indicate a set of
|
||||||
|
attributes. The meanings of the flags are:
|
||||||
|
|
||||||
|
Bit Name Description
|
||||||
|
---------------------------------------------------------------
|
||||||
|
0 SentByAcceptor When set, this flag indicates the sender
|
||||||
|
is the context acceptor. When not set,
|
||||||
|
it indicates the sender is the context
|
||||||
|
initiator.
|
||||||
|
1 Sealed When set in Wrap tokens, this flag
|
||||||
|
indicates confidentiality is provided
|
||||||
|
for. It MUST not be set in MIC and
|
||||||
|
context deletion tokens.
|
||||||
|
|
||||||
|
The rest of available bits are reserved for future use.
|
||||||
|
|
||||||
|
8.3. EC Field
|
||||||
|
|
||||||
|
The EC (Extra Count) field is a two-byte integer field expressed in
|
||||||
|
big endian order.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 6
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
In Wrap tokens with confidentiality, the EC field is used to encode
|
||||||
|
the size (in bytes) of the random filler, as described in section
|
||||||
|
8.4.
|
||||||
|
|
||||||
|
In Wrap tokens without confidentiality, the EC field is used to
|
||||||
|
encode the size (in bytes) of the trailing checksum, as described in
|
||||||
|
section 8.4.
|
||||||
|
|
||||||
|
When AES is used, the EC field contains the hex value 00 0C in Wrap
|
||||||
|
tokens without confidentiality, and 00 00 in Wrap tokens with
|
||||||
|
confidentiality.
|
||||||
|
|
||||||
|
8.4. Encryption and Checksum Operations
|
||||||
|
|
||||||
|
The encryption algorithms defined by the crypto profiles provide for
|
||||||
|
integrity protection. Therefore no separate checksum is needed.
|
||||||
|
|
||||||
|
The result of decryption can be longer than the original plaintext
|
||||||
|
[KCRYPTO] and the extra trailing bytes are called "crypto-system
|
||||||
|
garbage". However, given the size of any plaintext data, one can
|
||||||
|
always find the next (possibly larger) size so that, when padding
|
||||||
|
the to-be-encrypted text to that size, there will be no crypto-
|
||||||
|
system garbage added [KCRYPTO].
|
||||||
|
|
||||||
|
In Wrap tokens that provide for confidentiality, the "header" (the
|
||||||
|
first 16 bytes of the Wrap token) is appended to the plaintext data
|
||||||
|
before encryption. Random filler is inserted between the plaintext-
|
||||||
|
data and the "header", and there SHALL NOT be crypto-system garbage
|
||||||
|
added by the decryption operation. The resulting Wrap token is
|
||||||
|
{"header" | encrypt(plaintext-data | random-filler | "header")},
|
||||||
|
where encrypt() is the encryption operation (which provides for
|
||||||
|
integrity protection) defined in the crypto profile [KCRYPTO].
|
||||||
|
|
||||||
|
[A note from the design team (Sam, Nicolas, Ken, JK and Larry):
|
||||||
|
constraints need to be added to kcrypto to keep the header at the
|
||||||
|
end of the decrypted data. Without these constraints, we might have
|
||||||
|
the header pre-pended to the front of the data and encode an 8 byte
|
||||||
|
length for the plaintext data, which is less efficient.
|
||||||
|
|
||||||
|
Constraints to be added: Given the length of any plaintext data,
|
||||||
|
there should always exist the next (possibly larger) size for which,
|
||||||
|
when padding the to-be-encrypted data to that size, there will be no
|
||||||
|
cryptosystem garbage added, and the number of bytes needed to pad to
|
||||||
|
the next size is no larger than 64K. This is a small addition to
|
||||||
|
kcrypto and we will bring it up at the IETF last call for kcrypto]
|
||||||
|
|
||||||
|
In Wrap tokens that do not provide for confidentiality, the checksum
|
||||||
|
is calculated over the plaintext data concatenated with the token
|
||||||
|
header (the first 16 bytes of the Wrap token). The resulting Wrap
|
||||||
|
token is {"header" | plaintext-data | get_mic(plaintext-data |
|
||||||
|
"header")}, where get_mic() is the checksum operation defined in
|
||||||
|
the crypto profile [KCRYPTO].
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 7
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
The parameters for the key and the cipher-state in the encrypt() and
|
||||||
|
get_mic() operations have been omitted for brevity.
|
||||||
|
|
||||||
|
The resulting Wrap tokens bind the data to the token header,
|
||||||
|
including the sequence number and the directional indicator.
|
||||||
|
|
||||||
|
[With AEAD, Wrap tokens with confidentiality do not need to encrypt
|
||||||
|
the header and the overhead can be reduced slightly]
|
||||||
|
|
||||||
|
For MIC tokens, the checksum is first calculated over the token
|
||||||
|
header (the first 16 bytes of the MIC token) and then the to-be-
|
||||||
|
signed plaintext data.
|
||||||
|
|
||||||
|
For context deletion tokens, the checksum is calculated over the
|
||||||
|
token header (the first 16 bytes of the context deletion token).
|
||||||
|
|
||||||
|
When AES is used, the checksum algorithm is HMAC_SHA1_96 and the
|
||||||
|
checksum size is 12 bytes. Data is pre-pended with a 16 byte
|
||||||
|
confounder before encryption, and no padding is needed.
|
||||||
|
|
||||||
|
8.5. RRC Field
|
||||||
|
|
||||||
|
The RRC (Right Rotation Count) field in Wrap tokens is added to
|
||||||
|
allow the data to be encrypted in-place by existing [SSPI]
|
||||||
|
applications that do not provide an additional buffer for the
|
||||||
|
trailer (the cipher text after the in-place-encrypted data) in
|
||||||
|
addition to the buffer for the header (the cipher text before the
|
||||||
|
in-place-encrypted data). The resulting Wrap token in the previous
|
||||||
|
section, excluding the first 16 bytes of the token header, is
|
||||||
|
rotated to the right by "RRC" bytes. The net result is that "RRC"
|
||||||
|
bytes of trailing octets are moved toward the header. Consider the
|
||||||
|
following as an example of this rotation operation: Assume that the
|
||||||
|
RRC value is 3 and the token before the rotation is {"header" | aa |
|
||||||
|
bb | cc | dd | ee | ff | gg | hh}, the token after rotation would be
|
||||||
|
{"header" | ff | gg | hh | aa | bb | cc | dd | ee }, where {aa | bb
|
||||||
|
| cc |...| hh} is used to indicate the byte sequence.
|
||||||
|
|
||||||
|
The RRC field is expressed as a two-byte integer in big endian
|
||||||
|
order.
|
||||||
|
|
||||||
|
The rotation count value is chosen by the sender based on
|
||||||
|
implementation details, and the receiver MUST be able to interpret
|
||||||
|
all possible rotation count values.
|
||||||
|
|
||||||
|
8.6. Message Layout for Per-message and Context Deletion Tokens
|
||||||
|
|
||||||
|
The new message layouts are as follows.
|
||||||
|
|
||||||
|
MIC Token:
|
||||||
|
|
||||||
|
Byte no Name Description
|
||||||
|
0..1 TOK_ID Identification field.
|
||||||
|
Tokens emitted by GSS_GetMIC()
|
||||||
|
contain the hex value 04 04 in
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 8
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
this field.
|
||||||
|
2 Flags Attributes field, as described in
|
||||||
|
Section 8.2.
|
||||||
|
3..7 Filler Contains 5 bytes of hex value FF.
|
||||||
|
8..15 SND_SEQ Sequence number field in
|
||||||
|
cleartext, in big endian order.
|
||||||
|
16..last SGN_CKSUM Checksum of byte 0..15 and the
|
||||||
|
"to-be-signed" data, where the
|
||||||
|
checksum algorithm is defined by
|
||||||
|
the crypto profile for the
|
||||||
|
session key or subkey.
|
||||||
|
|
||||||
|
|
||||||
|
The Filler field is included in the checksum calculation for
|
||||||
|
simplicity. This is common to both MIC and context deletion token
|
||||||
|
checksum calculations.
|
||||||
|
|
||||||
|
Wrap Token:
|
||||||
|
|
||||||
|
Byte no Name Description
|
||||||
|
0..1 TOK_ID Identification field.
|
||||||
|
Tokens emitted by GSS_Wrap()
|
||||||
|
contain the hex value 05 04
|
||||||
|
in this field.
|
||||||
|
2 Flags Attributes field, as described in
|
||||||
|
Section 8.2.
|
||||||
|
3 Filler Contains the hex value FF.
|
||||||
|
4..5 EC Contains the "extra count" field,
|
||||||
|
in big endian order as described in
|
||||||
|
section 8.3.
|
||||||
|
6..7 RRC Contains the "right rotation
|
||||||
|
count" in big endian order, as
|
||||||
|
described in section 8.5.
|
||||||
|
8..15 SND_SEQ Sequence number field in
|
||||||
|
cleartext, in big endian order.
|
||||||
|
16..last Data Encrypted data or (plaintext data +
|
||||||
|
checksum), as described in section
|
||||||
|
8.4, where the encryption or
|
||||||
|
checksum algorithm is defined by
|
||||||
|
the crypto profile for the session
|
||||||
|
key or subkey.
|
||||||
|
|
||||||
|
|
||||||
|
Context Deletion Token:
|
||||||
|
|
||||||
|
Byte no Name Description
|
||||||
|
0..1 TOK_ID Identification field.
|
||||||
|
Tokens emitted by
|
||||||
|
GSS_Delete_sec_context() contain
|
||||||
|
the hex value 04 05 in this
|
||||||
|
field.
|
||||||
|
2 Flags Attributes field, as described in
|
||||||
|
Section 8.2.
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 9
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
3..7 Filler Contains 5 bytes of hex value FF.
|
||||||
|
8..15 SND_SEQ Sequence number field in
|
||||||
|
cleartext, in big endian order.
|
||||||
|
16..N SGN_CKSUM Checksum of byte 0..15, where the
|
||||||
|
checksum algorithm is defined by
|
||||||
|
the crypto profile for the
|
||||||
|
session key or subkey.
|
||||||
|
|
||||||
|
|
||||||
|
9. Parameter Definitions
|
||||||
|
|
||||||
|
This section defines parameter values used by the Kerberos V5 GSS-
|
||||||
|
API mechanism. It defines interface elements in support of
|
||||||
|
portability, and assumes use of C language bindings per [RFC-2744].
|
||||||
|
|
||||||
|
9.1. Minor Status Codes
|
||||||
|
|
||||||
|
This section recommends common symbolic names for minor_status
|
||||||
|
values to be returned by the Kerberos V5 GSS-API mechanism. Use of
|
||||||
|
these definitions will enable independent implementers to enhance
|
||||||
|
application portability across different implementations of the
|
||||||
|
mechanism defined in this specification. (In all cases,
|
||||||
|
implementations of GSS_Display_status() will enable callers to
|
||||||
|
convert minor_status indicators to text representations.) Each
|
||||||
|
implementation should make available, through include files or other
|
||||||
|
means, a facility to translate these symbolic names into the
|
||||||
|
concrete values which a particular GSS-API implementation uses to
|
||||||
|
represent the minor_status values specified in this section.
|
||||||
|
|
||||||
|
It is recognized that this list may grow over time, and that the
|
||||||
|
need for additional minor_status codes specific to particular
|
||||||
|
implementations may arise. It is recommended, however, that
|
||||||
|
implementations should return a minor_status value as defined on a
|
||||||
|
mechanism-wide basis within this section when that code is
|
||||||
|
accurately representative of reportable status rather than using a
|
||||||
|
separate, implementation-defined code.
|
||||||
|
|
||||||
|
9.1.1. Non-Kerberos-specific codes
|
||||||
|
|
||||||
|
GSS_KRB5_S_G_BAD_SERVICE_NAME
|
||||||
|
/* "No @ in SERVICE-NAME name string" */
|
||||||
|
GSS_KRB5_S_G_BAD_STRING_UID
|
||||||
|
/* "STRING-UID-NAME contains nondigits" */
|
||||||
|
GSS_KRB5_S_G_NOUSER
|
||||||
|
/* "UID does not resolve to username" */
|
||||||
|
GSS_KRB5_S_G_VALIDATE_FAILED
|
||||||
|
/* "Validation error" */
|
||||||
|
GSS_KRB5_S_G_BUFFER_ALLOC
|
||||||
|
/* "Couldn't allocate gss_buffer_t data" */
|
||||||
|
GSS_KRB5_S_G_BAD_MSG_CTX
|
||||||
|
/* "Message context invalid" */
|
||||||
|
GSS_KRB5_S_G_WRONG_SIZE
|
||||||
|
/* "Buffer is the wrong size" */
|
||||||
|
GSS_KRB5_S_G_BAD_USAGE
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 10
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
/* "Credential usage type is unknown" */
|
||||||
|
GSS_KRB5_S_G_UNKNOWN_QOP
|
||||||
|
/* "Unknown quality of protection specified" */
|
||||||
|
|
||||||
|
9.1.2. Kerberos-specific-codes
|
||||||
|
|
||||||
|
GSS_KRB5_S_KG_CCACHE_NOMATCH
|
||||||
|
/* "Principal in credential cache does not match desired
|
||||||
|
name" */
|
||||||
|
GSS_KRB5_S_KG_KEYTAB_NOMATCH
|
||||||
|
/* "No principal in keytab matches desired name" */
|
||||||
|
GSS_KRB5_S_KG_TGT_MISSING
|
||||||
|
/* "Credential cache has no TGT" */
|
||||||
|
GSS_KRB5_S_KG_NO_SUBKEY
|
||||||
|
/* "Authenticator has no subkey" */
|
||||||
|
GSS_KRB5_S_KG_CONTEXT_ESTABLISHED
|
||||||
|
/* "Context is already fully established" */
|
||||||
|
GSS_KRB5_S_KG_BAD_SIGN_TYPE
|
||||||
|
/* "Unknown signature type in token" */
|
||||||
|
GSS_KRB5_S_KG_BAD_LENGTH
|
||||||
|
/* "Invalid field length in token" */
|
||||||
|
GSS_KRB5_S_KG_CTX_INCOMPLETE
|
||||||
|
/* "Attempt to use incomplete security context" */
|
||||||
|
|
||||||
|
9.2. Buffer Sizes
|
||||||
|
|
||||||
|
All implementations of this specification shall be capable of
|
||||||
|
accepting buffers of at least 16K bytes as input to GSS_GetMIC(),
|
||||||
|
GSS_VerifyMIC(), and GSS_Wrap(), and shall be capable of accepting
|
||||||
|
the output_token generated by GSS_Wrap() for a 16K byte input buffer
|
||||||
|
as input to GSS_Unwrap(). Support for larger buffer sizes is
|
||||||
|
optional but recommended.
|
||||||
|
|
||||||
|
10. Backwards Compatibility Considerations
|
||||||
|
|
||||||
|
The new token formats defined in this document will only be
|
||||||
|
recognized by new implementations. To address this, implementations
|
||||||
|
can always use the explicit sign or seal algorithm in [GSSAPI-KRB5]
|
||||||
|
when the key type corresponds to "older" algorithms. An alternative
|
||||||
|
approach might be to retry sending the message with the sign or seal
|
||||||
|
algorithm explicitly defined as in [GSSAPI-KRB5]. However this
|
||||||
|
would require the use of a mechanism such as [RFC-2478] to securely
|
||||||
|
negotiate the algorithm or the use out of band mechanism to choose
|
||||||
|
appropriate algorithms. For this reason, it is RECOMMENDED that the
|
||||||
|
new token formats defined in this document can be used only if both
|
||||||
|
peers are known during context negotiation to support the new
|
||||||
|
mechanism (either because of the use of "new" enctypes or because of
|
||||||
|
the use of Kerberos V extensions).
|
||||||
|
|
||||||
|
11. Security Considerations
|
||||||
|
|
||||||
|
It is possible that the KDC returns a session-key type that is not
|
||||||
|
supported by the GSSAPI implementation (either on the client and the
|
||||||
|
server). In this case the implementation MUST not try to use the key
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 11
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
with a supported cryptosystem. This will ensure that no security
|
||||||
|
weaknesses arise due to the use of an inappropriate key with an
|
||||||
|
encryption algorithm.
|
||||||
|
|
||||||
|
In addition the security problem described in [3DES] arising from
|
||||||
|
the use of a service implementation with a GSSAPI mechanism
|
||||||
|
supporting only DES and a Kerberos mechanism supporting both DES and
|
||||||
|
Triple DES is actually a more generic one. It arises whenever the
|
||||||
|
GSSAPI implementation does not support a stronger cryptosystem
|
||||||
|
supported by the Kerberos mechanism. KDC administrators desiring to
|
||||||
|
limit the session key types to support interoperability with such
|
||||||
|
GSSAPI implementations should carefully weigh the reduction in
|
||||||
|
protection offered by such mechanisms against the benefits of
|
||||||
|
interoperability.
|
||||||
|
|
||||||
|
|
||||||
|
12. Acknowledgments
|
||||||
|
|
||||||
|
The authors wish to acknowledge the contributions from the following
|
||||||
|
individuals:
|
||||||
|
|
||||||
|
Ken Raeburn and Nicolas Willams corrected many of our errors in the
|
||||||
|
use of generic profiles and were instrumental in the creation of this
|
||||||
|
draft.
|
||||||
|
|
||||||
|
Sam Hartman and Ken Raeburn suggested the "floating trailer" idea.
|
||||||
|
|
||||||
|
Sam Hartman and Nicolas Williams recommended the replacing our
|
||||||
|
earlier key derivation function for directional keys with different
|
||||||
|
key usage numbers for each direction as well as retaining the
|
||||||
|
directional bit for maximum compatibility.
|
||||||
|
|
||||||
|
Paul Leach provided numerous suggestions and comments.
|
||||||
|
|
||||||
|
Scott Field, Richard Ward, Dan Simon also provided valuable inputs on
|
||||||
|
this draft.
|
||||||
|
|
||||||
|
13. References
|
||||||
|
|
||||||
|
13.1. Normative References
|
||||||
|
|
||||||
|
[RFC-2026] Bradner, S., "The Internet Standards Process -- Revision
|
||||||
|
3", BCP 9, RFC 2026, October 1996.
|
||||||
|
|
||||||
|
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
|
||||||
|
Requirement Levels", BCP 14, RFC 2119, March 1997.
|
||||||
|
|
||||||
|
[AES] National Institute of Standards and Technology, U.S.
|
||||||
|
Department of Commerce, "Advanced Encryption Standard", Federal
|
||||||
|
Information Processing Standards Publication 197, Washington, DC,
|
||||||
|
November 2001.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 12
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
[AES-KRB5] Raeburn, K., "AES Encryption for Kerberos 5", draft-
|
||||||
|
raeburn-krb-rijndael-krb-05.txt, June 2003. Work in progress.
|
||||||
|
|
||||||
|
[3DES] Raeburn, K., "Triple-DES Support for the Kerberos 5 GSSAPI
|
||||||
|
Mechanism", draft-raeburn-gssapi-krb5-3des-XX.txt in the MIT
|
||||||
|
distribution, June 2000.
|
||||||
|
|
||||||
|
[RFC-2743] Linn, J., "Generic Security Service Application Program
|
||||||
|
Interface Version 2, Update 1", RFC 2743, January 2000.
|
||||||
|
|
||||||
|
[RFC-2744] Wray, J., "Generic Security Service API Version 2 : C-
|
||||||
|
bindings", RFC 2744, January 2000.
|
||||||
|
|
||||||
|
[RFC-1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
|
||||||
|
RFC 1964, June 1996.
|
||||||
|
|
||||||
|
[KCRYPTO] Raeburn, K., "Encryption and Checksum Specifications for
|
||||||
|
Kerberos 5", draft-ietf-krb-wg-crypto-05.txt, June, 2003. Work in
|
||||||
|
progress.
|
||||||
|
|
||||||
|
[KRBCLAR] Neuman, C., Kohl, J., Ts'o T., Yu T., Hartman, S.,
|
||||||
|
Raeburn, K., "The Kerveros Network Authentication Service (V5)",
|
||||||
|
draft-ietf-krb-wg-kerberos-clarifications-04.txt, February 2002.
|
||||||
|
Work in progress.
|
||||||
|
|
||||||
|
[RFC-2478] Baize, E., Pinkas D., "The Simple and Protected GSS-API
|
||||||
|
Negotiation Mechanism.", RFC 2478, December 1998.
|
||||||
|
|
||||||
|
13.2. Informative References
|
||||||
|
|
||||||
|
[SSPI] Leach, P., Security Service Provider Interface, MSDN, April
|
||||||
|
2003
|
||||||
|
|
||||||
|
14. Author's Address
|
||||||
|
|
||||||
|
Larry Zhu
|
||||||
|
One Microsoft Way
|
||||||
|
Redmond, WA 98052 - USA
|
||||||
|
EMail: LZhu@microsoft.com
|
||||||
|
|
||||||
|
Karthik Jaganathan
|
||||||
|
One Microsoft Way
|
||||||
|
Redmond, WA 98052 - USA
|
||||||
|
EMail: karthikj@microsoft.com
|
||||||
|
|
||||||
|
Sam Hartman
|
||||||
|
Massachusetts Institute of Technology
|
||||||
|
77 Massachusetts Avenue
|
||||||
|
Cambridge, MA 02139 - USA
|
||||||
|
Email: hartmans@MIT.EDU
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 13
|
||||||
|
Kerberos Version 5 GSS-API August 2003
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Full Copyright Statement
|
||||||
|
|
||||||
|
"Copyright (C) The Internet Society (date). 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 revoked by the Internet Society or its successors or
|
||||||
|
assigns.
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
Zhu Standards Track - February 16, 2004 14
|
Reference in New Issue
Block a user