Hypothesis Testing
Contents
- 1 Introduction
- 2 Methodology
- 3 Base Hypothesis
- 4 Hypothesis 1: Z340 is a monoalphabetic homophonic substitution cipher.
- 5 Hypothesis 2: Columnar transposition was applied to the plaintext prior to homophonic substitution
- 6 Hypothesis 2: Scytale transposition was applied to the plaintext prior to homophonic substitution
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? There are many schemes to choose from. People have tried many different schemes, but there is not yet a comprehensive study over which schemes are feasible. Moreover, it is not clear if a particular scheme can be broken if Z340 uses it. So we need a comprehensive way to answer these questions about a scheme:
- Is it possible to create a Z340-like cipher using this scheme?
- Can a Z340-like cipher created using this scheme be cracked reliably?
- Is this scheme more likely than other schemes to produce some of the unusual features observed in Z340?
Methodology
The strategy presented here is the following:
- First, define a hypothesis for Z340's encipherment scheme. The hypothesis is a collection of statements about properties of Z340's plaintext, and the operations performed on the plaintext to turn it into ciphertext.
- Create at least 100 test ciphers under the scheme.
- Guide the generation of test ciphers so that they contain statistical properties and features that are very similar to Z340.
- Cryptanalyze the test ciphers, and recover their plaintext messages.
- If all the test ciphers can be solved reliably, but the same procedure fails to solve Z340, then we have stronger evidence that the chosen hypothesis is false.
Base Hypothesis
TODO
Hypothesis 1: Z340 is a monoalphabetic homophonic substitution cipher.
TODO
Hypothesis 2: Columnar transposition was applied to the plaintext prior to homophonic substitution
TODO
Hypothesis 2: Scytale transposition was applied to the plaintext prior to homophonic substitution
TODO
