Information-Theoretical Analysis of Two Shannon's Ciphers

TL;DR

This paper analyzes two of Shannon's cipher methods using information theory, proposing estimations for cipher security and decoding probabilities without the key.

Contribution

It introduces generalized running key ciphers and provides new analytical tools for evaluating Shannon's cipher methods.

Findings

Estimated cipher equivocation for the analyzed methods

Calculated probability of correct deciphering without the key

Extended Shannon's analysis to generalized cipher models

Abstract

We describe generalized running key ciphers and apply them for analysis of two Shannon's methods. In particular, we suggest some estimation of the cipher equivocation and the probability of correct deciphering without key.