Twofish is a encryption method designed by Counterpane Labs, namely by John Kelsey, Bruce Schneier, David Wagner, Niels Ferguson, Chris Hall and Doug Whiting. Twofish algorithm was one of five finalists of AES (Encryption Standard). Twofish encryption algorithm is available for free use.
How twofish algorithm works?
The following explanation is highly techinical and is based on wikipedia article
Twofish is symmetric algorithm with 128 bit block and 256 bit key size. What marks twofish algorithm distinctive is usage of pre-computed key-dependent S-boxes and complex key schedule. One half of an n-bit key is used as the actual encryption key and the other half of the n-bit key is used to modify the encryption algorithm (key-dependent S-boxes). Twofish algorithm takes some ideas from other algorithms, like the pseudo-Hadamard transform. Twofish algorithm use the same Feistel structure as DES.