A.V. Babash, D.S. Kudiyarov
RC4 is a consecutive combination of complete-cycle Moore machine and Mealy machine. Mealy machine’s state is a permutation from symmetric group Sn and integer from residue ring Zn. The proof that permutation sequence period is multiple of 2n-1 is given. A sufficient conditions for permutation sequence period to be a multiple of 2n are provided.