Tiger (hash function)

Tiger is a cryptographic hash function designed by Ross Anderson and Eli Biham in 1995 for efficiency on 64-bit platforms. It produces a 192-bit hash value, and truncated forms known as Tiger/128 and Tiger/160 can be used where a protocol expects a smaller hash. Tiger follows the Merkle-Damgård construction: a one-way compression function works on 64-bit words, keeping three words of state and processing eight words of data over 24 rounds that mix XOR, addition and subtraction, rotations and S-box lookups, with a fairly intricate key schedule. Its four large S-boxes, 8 KiB in total, make it fast in software but awkward to build in hardware or on microcontrollers. A variant, Tiger2, differs only in its padding byte. Tiger is widely used in Merkle hash tree form as the Tiger Tree Hash on the Direct Connect and Gnutella file sharing networks, and it was considered for the OpenPGP standard before RIPEMD-160 was chosen instead.