Phelix is a high-speed stream cipher with a built-in single-pass message authentication code (MAC) functionality, submitted in 2004 to the eSTREAM contest by , Bruce Schneier, Stefan Lucks, and . The cipher uses only the operations of addition modulo 232, exclusive or, and rotation by a fixed number of bits. Phelix uses a 256-bit key and a 128-bit nonce, claiming a design strength of 128 bits. Concerns have been raised over the ability to recover the secret key if the cipher is used incorrectly. (Wikipedia).