A Brief Guide to the Authentication of Cryptanalytic Claims

Abstract

Information theory provides powerful tools for the analysis of cryptographic systems. These tools may be used to discredit pseudo-cryptographic claims, validate legitimate claims, and assess whether a ciphertext is likely to be decipherable. Although information theory can be found in most cryptology textbooks, what is often lacking is practical guidance that addresses different types of classical cipher systems. This article presents information theory with a minimum of technical details, focusing on a few powerful concepts and several basic formulae. It demonstrates how to test various types of cryptographic systems. Of special concern is the difficulty of authenticating short ciphertexts. It proposes further work that would aid in the authentication of historical ciphers.