SHA-256 Length Extension Attack Simulator

Any hash built on the Merkle–Damgård construction — SHA-256, SHA-512, MD5 — lets an attacker who knows H(secret || message) and the length of message compute H(secret || message || glue_padding || extra) without ever learning secret. This is why H(secret || message) is an unsafe MAC construction; HMAC exists specifically to fix it. Run the attack below against a simulated vulnerable server.