Solution for the BlackHat Challenge

This write-up solves a network protocol analysis challenge by reversing a simple challenge–response authentication that computes MD5(R+secret), then using hashcat with a constrained charset to brute-force the shared secret from captured traffic and derive the session key. It highlights insecure protocol design (misuse of HMAC, short lowercase alphanumeric secret) and demonstrates practical offline cracking to authenticate and recover session material.