Padding Oracle Attack Simulator

CBC decryption that reports why padding failed — rather than just that it failed — leaks enough information to recover an entire ciphertext one byte at a time, with no key required. This is the same class of vulnerability behind POODLE and several historical TLS/SSL exploits. Paste a ciphertext produced by the AES/CBC visualizer, run the attack against the vulnerable oracle below, then flip to the fixed, constant-time oracle to see the same attack fail.