Blowfish Algorithm

Blowfish is a symmetric block cipher operating on 64 bit blocks with a variable key length from 32 to 448 bits, built as a sixteen round Feistel network with key-dependent S-boxes generated through an expensive key schedule designed to resist brute force attacks. Bruce Schneier designed it in 1993 as a fast, unpatented, freely available alternative to DES. Its 64 bit block size makes it vulnerable to birthday-bound attacks on very large amounts of data under one key, which led Schneier to later design the successor cipher Twofish with a larger block size.