John the Ripper -- Password Cracker

John the Ripper is designed to be both powerful and fast. It combines several cracking modes in one program, and is fully configurable for your particular needs (you can even define a custom cracking mode using the built-in compiler supporting a subset of C).

Out of the box, John supports (and autodetects) the following ciphertext formats: standard and double-length DES-based, BSDI's extended DES-based, FreeBSD's (and not only) MD5-based and OpenBSD's Blowfish-based.

With just one extra command (required to extract the passwords), John can crack AFS passwords and WinNT LM hashes.

Unlike other crackers, John doesn't use a crypt(3)-style routine. Instead, it has its own highly optimized modules for different ciphertext formats and architectures. Some of the algorithms used couldn't be implemented in a crypt(3)-style routine: they require a more powerful interface (bitslice DES is an example). Additionally, there're assembly routines for several processors and architectures (special Intel Pentium version, x86 with MMX, generic x86, Alpha EV4, SPARC V8).