draft-kamath-pppext-eap-mschapv2-00.txt

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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


   Whenever a Response packet is received, the authenticator compares
   the Response Value with its own calculation of the expected value. If
   the values match, then the authenticator MUST send a Success-Request
   packet, as described in Section 2.3.  If the values do not match, and
   if the error is retryable, then a Failure-Request packet MUST be sent
   as described in Section 2.5. If the values do not match, and the
   error is not retryable, then  a Failure-Request packet (described in
   Section 2.5) SHOULD be sent, or alternatively, the authentication MAY
   be  terminated (as described in Section 2.8) such as by sending an
   EAP Failure.

Name

   The Name field is a string of 0 to (theoretically) 256 case-sensitive
   ASCII characters which identifies the peer's user account name.  The
   Windows NT domain name may prefix the user's account name (e.g.
   BIGCO\johndoe where BIGCO is a Windows NT domain containing the user
   account johndoe).  If a domain is not provided, the backslash should
   also be omitted, (e.g. johndoe).  The Name SHOULD NOT be NUL or CR/LF
   terminated.  The size of the Name field is determined from the Length
   - Value-Size - 10.

2.3.  Success Request packet

If the value received in the Response field of the EAP MS-CHAP-V2
Response packet is equal to the expected value, then the implementation
MUST transmit an EAP MS-CHAP-V2 Request packet with the OpCode field set
to 3 (Success).

The format of the EAP MS-CHAP-v2 Success Request packet is shown below.
The fields are transmitted from left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |   Identifier  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   OpCode      |  MS-CHAPv2-ID |  MS-Length...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   MS-Length   |                    Message...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

   1 - Request






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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


Identifier

   The Identifier field is one octet.  The Identifier field MUST be the
   same if a Request packet is retransmitted due to a timeout while
   waiting for a Response.  Any new (non-retransmission) Requests MUST
   modify the Identifier field.  If a peer receives a duplicate Request
   for which it has already sent a Response, it MUST resend it's
   Response.  If a peer receives a duplicate Request before it has sent
   a Response to the initial Request (i.e. it's waiting for user input),
   it MUST silently discard the duplicate Request.

Length

   The Length field is two octets and indicates the length of the EAP
   packet including the Code, Identifier, Length, Type, OpCode, MS-
   CHAPv2-ID, MS-Length, and Message fields.  Octets outside the range
   of the Length field should be treated as Data Link Layer padding and
   should be ignored on reception.

Type

   26 - EAP MS-CHAP-V2

OpCode

   3 - Success

MS-CHAPv2-ID

   The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2
   responses with requests.  Typically, the MS-CHAPv2-ID field is the
   same as the Identifier field.

MS-Length

   The MS-Length field is two octets and MUST be set to the value of the
   Length field minus 5.

Message

   The Message field contains a 42-octet authenticator response string
   and a printable message.  The format of the message field is
   illustrated below.

      "S=<auth_string> M=<message>"

   The <auth_string> quantity is a 20 octet number encoded in ASCII as
   40 hexadecimal digits.  The hexadecimal digits A-F (if present) MUST



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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


   be uppercase.  This number is derived from the challenge from the
   Challenge packet, the Peer-Challenge and NT-Response fields from the
   Response packet, and the peer password as output by the routine
   GenerateAuthenticatorResponse() defined in [RFC2759], Section 8.7.
   The authenticating peer MUST verify the authenticator response when a
   Success packet is received.  The method for verifying the
   authenticator is described in [RFC2759], section 8.8.  If the
   authenticator response is either missing or incorrect, the peer MUST
   end the session without sending a response.

   The <message> quantity is human-readable text in the appropriate
   charset and language [RFC2484].

2.4.  Success Response packet

In the peer successfully validates the EAP MS-CHAP-V2 Success Request
packet sent by the authenticator, then it MUST respond with an EAP MS-
CHAP-V2 Success Response packet with the OpCode field set to 3
(Success).

The format of the EAP MS-CHAP-v2 Success Response packet is shown below.
The fields are transmitted from left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |   Identifier  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   OpCode      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

   2 - Response

Identifier

   The Identifier field is one octet and contains the value included in
   the EAP Request to which it responds.

Length

   6








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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


Type

   26 - EAP MS-CHAP-V2

OpCode

   3 - Success

2.5.  Failure Request packet

If the Value received in a Response is not equal to the expected value,
and the error is retryable, then  the implementation MUST transmit an
EAP MS-CHAP-v2 Request packet with the OpCode field set to 4 (Failure).
If the error is not retryable, then the implementation SHOULD transmit
an EAP MS-CHAP-v2 Failure Request packet, or it MAY terminate the
authentication (e.g. send an EAP Failure packet). The former approach is
preferable, since this enables the cause of the error to be
communicated.

The format of the EAP MS-CHAP-v2 Failure Request packet is shown below.
The fields are transmitted from left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |   Identifier  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   OpCode      |  MS-CHAPv2-ID |  MS-Length...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   MS-Length   |                    Message...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

   1 - Request

Identifier

   The Identifier field is one octet.  The Identifier field MUST be the
   same if a Request packet is retransmitted due to a timeout while
   waiting for a Response.  Any new (non-retransmission) Requests MUST
   modify the Identifier field.  If a peer receives a duplicate Request
   for which it has already sent a Response, it MUST resend it's
   Response.  If a peer receives a duplicate Request before it has sent
   a Response to the initial Request (i.e. it's waiting for user input),
   it MUST silently discard the duplicate Request.





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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


Length

   The Length field is two octets and indicates the length of the EAP
   packet including the Code, Identifier, Length, Type, OpCode, MS-
   CHAPv2-ID, MS-Length, and Message fields.  Octets outside the range
   of the Length field should be treated as Data Link Layer padding and
   should be ignored on reception.

Type

   26 - EAP MS-CHAP-V2

OpCode

   4 - Failure

MS-CHAPv2-ID

   The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2
   responses with requests. Typically, the MS-CHAPv2-ID field is the
   same as the Identifier field.

MS-Length

   The MS-Length field is two octets and MUST be set to the value of the
   Length field minus 5.

Message

   The Message field format is:

     "E=eeeeeeeeee R=r C=cccccccccccccccccccccccccccccccc V=vvvvvvvvvv M=<msg>"

   where

   The "eeeeeeeeee" is the ASCII representation of a decimal error code
   corresponding to one of those listed below, though implementations
   should deal with codes not on this list gracefully. The error code
   need not be 10 digits long.

        646 ERROR_RESTRICTED_LOGON_HOURS
        647 ERROR_ACCT_DISABLED
        648 ERROR_PASSWD_EXPIRED
        649 ERROR_NO_DIALIN_PERMISSION
        691 ERROR_AUTHENTICATION_FAILURE
        709 ERROR_CHANGING_PASSWORD

   The "r" is a single character ASCII flag set to '1' if a retry is



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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


   allowed, and '0' if not.  Typically, errors 646, 647, and 649 are
   non-retryable (R=0). When the authenticator sets this flag to '1' it
   disables short timeouts, expecting the peer to prompt the user for
   new credentials and resubmit the response. The
   "cccccccccccccccccccccccccccccccc" is the ASCII representation of a
   hexadecimal challenge value.  This field MUST be exactly 32 octets
   long and MUST be present.

   The "vvvvvvvvvv" is the ASCII representation of a decimal version
   code (need not be 10 digits) indicating the password changing
   protocol version supported on the server.  For EAP MS-CHAP-V2, this
   value MUSTalways be 3.

   <msg> is human-readable text in the appropriate charset and language
   [RFC2484].

2.6.  Failure Response packet

When the peer receives a Failure Request packet that is retryable (R=1),
the authentication MAY be retried. For example, a new Response packet,
or Change Password packet MAY be sent. In these cases a Failure Response
packet is not sent.

However, if the EAP MS-CHAPv2 Failure Request is non-retryable (R=0),
then the peer SHOULD transmit an EAP MS-CHAP-v2 Response packet with the
OpCode field set to 4 (Failure). The format of the EAP MS-CHAP-v2
Failure Response packet is shown below. The fields are transmitted from
left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |   Identifier  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   OpCode      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

   2 - Response

Identifier

   The Identifier field is one octet and contains the value included in
   the EAP Request to which it responds.






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INTERNET-DRAFT                EAP MS-CHAPv2             2 September 2002


Length

   6

Type

   26 - EAP MS-CHAP-V2

OpCode

   4 - Failure

2.7.  Change-Password packet

The Change-Password packet does not appear in either standard CHAP or
MS-CHAP-V1.  It allows the peer to change the password on the account
specified in the preceding Response packet.  The Change-Password packet
should be sent only if the authenticator reports ERROR_PASSWD_EXPIRED
(E=648) in the Message field of the Failure packet.

The format of the EAP MS-CHAP-v2 Change Password packet is shown below.
The fields are transmitted from left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |   Identifier  |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   OpCode      |  MS-CHAPv2-ID |  MS-Length...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   MS-Length   |                    Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

   2 - Response

Identifier

   The Identifier field is one octet and aids in matching responses with
   requests.  The value is the Identifier of the received Failure packet
   to which this packet responds.

Length

   The Length field is two octets and indicates the length of the EAP
   packet including the Code, Identifier, Length, Type, OpCode, MS-
   CHAPv2-ID, MS-Length and Data  fields.  Octets outside the range of



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   the Length field should be treated as Data Link Layer padding and
   should be ignored on reception. For the Change Password packet, the
   length = 591.

Type

   26 - EAP MS-CHAP-V2

OpCode

   7 - Change Password

MS-CHAPv2-ID

   The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2
   responses with requests.  Typically, the MS-CHAPv2-ID field is the
   same as the Identifier field.

MS-Length

   The MS-Length field is two octets and MUST be set to the value of the
   Length field minus 5.

Data

   The Data field is 582 octets in length, and is subdivided as follows:

        516 octets : Encrypted-Password
         16 octets : Encrypted-Hash
         16 octets : Peer-Challenge
          8 octets : Reserved
         24 octets : NT-Response
          2-octet  : Flags

Encrypted-Password

   The Encrypted-Password field is 516 octets in length, and contains
   the PWBLOCK form of the new Windows NT password encrypted with the
   old Windows NT password hash, as output by the
   NewPasswordEncryptedWithOldNtPasswordHash() routine defined in
   [RFC2759], Section 8.9.

Encrypted-Hash

   The Encrypted-Hash field is 16 octets in length and contains the old
   Windows NT password hash encrypted with the new Windows NT password
   hash, as output by the
   OldNtPasswordHashEncryptedWithNewNtPasswordHash() routine, defined in



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