3.1.5.2.1 Client Receives a CHALLENGE_MESSAGE

When the client receives a CHALLENGE_MESSAGE, it MUST produce a challenge response and an encrypted session key. The client MUST send the negotiated features (flags), the user name, the user's domain, the client part of the challenge, the challenge response, and the encrypted session key to the server. This message is sent to the server as an AUTHENTICATE_MESSAGE.

If the ClientBlocked == TRUE and targ_name ([RFC2743] section 2.2.1) does not equal any of the ClientBlockExceptions server names, then the NTLM client MUST return STATUS_NOT_SUPPORTED to the client application.<50>

If NTLM v2 authentication is used and the CHALLENGE_MESSAGE contains a TargetInfo field, the client SHOULD NOT send the LmChallengeResponse field and SHOULD set the LmChallengeResponseLen and LmChallenResponseMaxLen fields in the AUTHENTICATE_MESSAGE to zero.<51>

If NTLM v2 authentication is used, the client SHOULD send the timestamp in the AUTHENTICATE_MESSAGE.<52>

 If there exists a CHALLENGE_MESSAGE.TargetInfo.AvId ==
 MsvAvTimestamp
      Set Time to CHALLENGE_MESSAGE.TargetInfo.Value of the AVPair
 ELSE
      Set Time to Currenttime
 Endif
  

If the CHALLENGE_MESSAGE TargetInfo field (section 2.2.1.2) has an MsvAvTimestamp present, the client SHOULD provide a MIC<53>:

  • If there is an AV_PAIR structure (section 2.2.2.1) with the AvId field set to MsvAvFlags,

    • then in the Value field, set bit 0x2 to 1.

    • else add an AV_PAIR structure (section 2.2.2.1) and set the AvId field to MsvAvFlags and the Value field bit 0x2 to 1.

  • Populate the MIC field with the MIC, where

     Set MIC to HMAC_MD5(ExportedSessionKey, ConcatenationOf(
          CHALLENGE_MESSAGE, AUTHENTICATE_MESSAGE))
    

The client SHOULD send the channel binding AV_PAIR <54>:

  • If the CHALLENGE_MESSAGE contains a TargetInfo field (section 2.2.1.2)

    • If the ClientChannelBindingsUnhashed (section 3.1.1.2) is not NULL

      • Add an AV_PAIR structure (section 2.2.2.1) and set the AvId field to MsvAvChannelBindings and the Value field to MD5_HASH(ClientChannelBindingsUnhashed).

      • Else add an AV_PAIR structure (section 2.2.2.1) and set the AvId field to MsvAvChannelBindings and the Value field to Z(16).

    • If ClientSuppliedTargetName (section 3.1.1.2) is not NULL

      • Add an AV_PAIR structure (section 2.2.2.1) and set the AvId field to MsvAvTargetName and the Value field to ClientSuppliedTargetName without terminating NULL. If UnverifiedTargetName (section 3.1.1.2) is TRUE, then in AvId field = MsvAvFlags set 0x00000004 bit.<55>

      • Else add an AV_PAIR structure (section 2.2.2.1) and set the AvId field to MsvAvTargetName and the Value field to an empty string without terminating NULL.

When this process is complete, the client MUST send the AUTHENTICATE_MESSAGE to the server, embedded in an application protocol message, and encoded as specified by that application protocol.

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