Two linear distinguishing attacks on VMPC and RC4A and weakness of RC4 family of stream ciphers

Abstract

At FSE 2004 two new stream ciphers VMPC and RC4A have been proposed. VMPC is a generalisation of the stream cipher RC4, whereas RC4A is an attempt to increase the security of RC4 by introducing an additional permuter in the design. This paper is the first work presenting attacks on VMPC and RC4A. We propose two linear distinguishing attacks, one on VMPC of complexity 2 54, and one on RC4A of complexity 258. We investigate the RC4 family of stream ciphers and show some theoretical weaknesses of such constructions. © International Association for Cryptologic Research 2005.