Rekeying Issues in the MUGI Stream Cipher

MUGI [15] is a word-based stream cipher designed for 64bit architectures. It uses a 128-bit master key and a 128-bit initialization vector to populate a large non-linear feedback shift register (NLFSR) and additional non-linear state (NLS). In standard benchmarks on 32-bit processors, MUGI suffers from poor key agility because it is implemented on an architecture for which it is not designed, and because its NLFSR is too large relative to the size of its master key. This paper proposes a variant of MUGI, entitled MUGI-M, to enhance key agility, and concludes with an analysis of its security and performance characteristics.