5.1 Security Considerations for Implementers
NTLM does not support any recent cryptographic methods, such as AES or SHA-256. It uses cyclic redundancy check (CRC) or message digest algorithms ([RFC1321]) for integrity, and it uses RC4 for encryption. Deriving a key from a password is as specified in [RFC1320] and [FIPS46-2]. Therefore, applications are generally advised not to use NTLM.<81>
The NTLM server does not require the NTLM client to send the MIC, but sending the MIC when the timestamp is present greatly increases security. Although implementations of NLMP will work without support for MIC, they will be vulnerable to message tampering.
The use of NullSession results in a SessionBaseKey with all zeroes, which does not provide security. Therefore, applications are generally advised not to use NullSession.