Homophonic coding with logarithmic memory size

Abstract

Homophonic coding, introduced in [1, 2], is refered to as a means of constructing unbreakable secret-key cipher systems. In [3] a homophonic coding method has been proposed that provides arbitrarily small redundancy r with the size of memory and computation time growing as 0(1/r) and 0(log2 1/r log log 1/r), respectively, as r → 0, not more than 4r random bits being used on average. In the present, paper, we suggest a method for which the memory size and computation time grow as 0(log 1/r) and 0(log 1/r log log 1/r log log log a/r), respectively, as r → 0, the average number of random bits being approx. 2 + r. We also propose a homophonic coding scheme which meets both specified redundancy and a number of random bits.