Rabbit: A New High-Performance Stream Cipher. We present a new stream cipher, Rabbit, based on iterating a set of coupled non-linear functions. Rabbit is characterized by a high performance in software with a measured encryption/decryption speed of 3.7 clock cycles per byte on a Pentium III processor. We have performed detailed security analysis, in particular, correlation analysis and algebraic investigations. The cryptanalysis of Rabbit did not reveal an attack better than exhaustive key search.