Hypothesis Testing

Introduction

The Zodiac Killer's 340-character cryptogram (referred to here as Z340) has many things in common with his 408-character cryptogram (Z408), but still remains unsolved. It seems rather evident that Z340 is not constructed using the same method as Z408, otherwise it would have been solved by now. Within the last 10 years or so, many software tools have been built to effectively solve homophonic substitution ciphers that have the same properties as Z408. If Z340 was a simple homophonic substitution cipher, it would have been solved by now by one of the numerous manual or automatic attempts.

Since Z340 remains unsolved, we must consider the possibility that some other scheme is used in its construction. How do we rule them out? Many people have suggested different types of schemes

Base Hypothesis

= Hypothesis 1: Z340 is a monoalphabetic homophonic substitution cipher.

= Hypothesis 2: Columnar transposition was applied to the plaintext prior to homophonic substitution

= Hypothesis 2: Scytale transposition was applied to the plaintext prior to homophonic substitution