Publication Date

2009

Degree Type

Master's Project

Degree Name

Master of Science (MS)

Department

Computer Science

Abstract

The Zodiac 340 cipher is one of the most famous unsolved ciphers of all time. It was allegedly written by “the Zodiac”, whose identity remains unknown to date. The Zodiac was a serial killer who killed a number of people in and around the San Francisco Bay area during the 1960s. He is confirmed to have seven victims, two of whom survived [1], although in taunting letters to the news media he claims to have killed 37 people. During this time, an encrypted message known as the Zodiac 408 cipher was mailed to 3 different newspapers in the San Francisco bay area. This was a homophonic cipher and was successfully decoded. Within a few days he sent out another cipher that was 340 characters long [4]. This cipher, which is known as the Zodiac 340 cipher, is unsolved to date. Many cryptologists have tried to crack this cipher but with no success. In this project, we implemented a novel genetic algorithm in an attempt to crack the Zodiac 340 cipher. We have attacked the cipher as a homophonic cipher where each cipher symbol is mapped to only a single English letter, but each English letter can be mapped to multiple cipher symbols. In the genetic algorithm, we implemented two variants of crossover: simple and intelligent. The simple crossover looks for commonly occurring substrings, without looking for actual English words in a putative decrypt. The intelligent crossover counts the number of actual English words that can be found in a putative decrypt when evaluating each solution. We implemented a dictionary lookup for quickly identifying English words for the intelligent crossover. The genetic algorithm using a combination of simple and intelligent crossovers was able to identify many English words in various putative decrypts but no solution was found.

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