Which authentication protocol is the predecessor of Kerberos?

The correct answer is NTLM, which stands for NT LAN Manager. NTLM is a challenge-response authentication protocol used in earlier Microsoft operating systems for authenticating users and systems. It was primarily utilized before the introduction of Kerberos in Windows 2000 and serves as a precursor to it in many ways.

NTLM operates through a series of challenges and secure responses, and while it was effective in its time, it has several security weaknesses compared to Kerberos. Kerberos was designed to provide a more secure method of authentication by using tickets for authentication, which mitigates several attacks that NTLM is vulnerable to, such as replay attacks and pass-the-hash attacks.

This context highlights the historical importance of NTLM within the development of authentication protocols, showing how it laid some foundational principles that were ultimately improved upon with the introduction of Kerberos. Thus, understanding NTLM's role is essential in the study of authentication protocols and their evolution in network security practices.