Blowfish is a symmetric block cipher algorithm designed by Bruce Schneier in 1993. It operates on 64-bit blocks with variable key lengths up to 448 bits, making it suitable for both domestic and exportable use. The structure consists of two main parts: the key-expansion part and the data-encryption part. Key expansion converts a variable-length key into several subkey arrays totaling 4168 bytes. Data encryption occurs via a 16-round Feistel network. Each round includes a key-dependent permutation and a key- and data-dependent substitution. All operations are XORs and additions on 32-bit words. The only additional operations are four indexed array data lookups per round. Blowfish’s speed and security have been extensively analyzed and it remains a strong algorithm choice.
