NTLM

Hello Shri,

NTLM or NT Lan Manager is an authentication protocol.

There are many authentication protocols such as Basic, Radius, Kerberos,... used in windows network to authenticate users/machines.

NTLM belongs to the "challenge/response" protocol family, which means that :

1.First, the client sends to the server a NEGOTIATE_MESSAGE

2.The server responds with CHALLENGE_MESSAGE

3.Finally, the client responds to the challenge with an AUTHENTICATE_MESSAGE

For more details you can check on internet there are many articles about this protocol.