3.4.4.1 Without Extended Session Security

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When Extended Session Security (NTLMSSP_NEGOTIATE_EXTENDED_SESSIONSECURITY) is not negotiated and session security (NTLMSSP_NEGOTIATE_SIGN or NTLMSSP_NEGOTIATE_SEAL) is negotiated, the message signature for NTLM without extended session security is a 16-byte value that contains the following components, as specified by the NTLMSSP_MESSAGE_SIGNATURE structure (section 2.2.2.9.1):

  • A 4-byte version-number value that is set to 1 (Version).

  • A 4-byte random pad.

  • The 4-bytes of the message's CRC32 (Checksum).

  • The 4-byte sequence number (SeqNum).

If message integrity is negotiated, the message signature is calculated as follows:

 -- Input: 
 --   SigningKey - The key used to sign the message.
 --   SealingKey - The key used to seal the message or checksum.
 --   RandomPad - A random number provided by the client. Typically 0.
 --   Message - The message being sent between the client and server.
 --   SeqNum - Defined in section 3.1.1.
 --   Handle - The handle to a key state structure corresponding to the
 --   current state of the SealingKey
 --
 -- Output:
 --   An NTLMSSP_MESSAGE_SIGNATURE structure whose fields are defined 
      in section 2.2.2.9.
 --   SeqNum - Defined in section 3.1.1.
 --
 -- Functions used: 
 --   ConcatenationOf() - Defined in Section 6.
 --   RC4() - Defined in Section 6.
 --   CRC32() - Defined in Section 6.
  
 Define MAC(Handle, SigningKey, SeqNum, Message) as
      Set NTLMSSP_MESSAGE_SIGNATURE.Version to 0x00000001
      Set NTLMSSP_MESSAGE_SIGNATURE.Checksum to CRC32(Message)
      Set NTLMSSP_MESSAGE_SIGNATURE.RandomPad RC4(Handle, RandomPad)
      Set NTLMSSP_MESSAGE_SIGNATURE.Checksum to RC4(Handle,
          NTLMSSP_MESSAGE_SIGNATURE.Checksum)
      Set NTLMSSP_MESSAGE_SIGNATURE.SeqNum to RC4(Handle, 0x00000000)
      If (connection oriented)
           Set NTLMSSP_MESSAGE_SIGNATURE.SeqNum to
               NTLMSSP_MESSAGE_SIGNATURE.SeqNum XOR SeqNum
           Set SeqNum to SeqNum + 1
      Else
           Set NTLMSSP_MESSAGE_SIGNATURE.SeqNum to
               NTLMSSP_MESSAGE_SIGNATURE.SeqNum XOR
               (application supplied SeqNum)
      Endif
      Set NTLMSSP_MESSAGE_SIGNATURE.RandomPad to 0
  
 EndDefine