Cipher Cross-off List

Previous studies into the Tamam Shud case have concluded that the mysterious code left behind is not just random letters; it is in fact a code. This raises the question: What code was used in encrypting this code? This page is aimed at addressing this question. The Cipher Cross-off list is a place where cipher schemes are listed that have been identified as potentially being used in creating the Somerton Man's code. As part of our project, we will be methodically investigating many of these listed ciphers to see if we can rule them out as being used in the encryption of the code.

Cipher Cross-off List

Random Sequence of letters
Initial letters of an unordered list
Initial letters of a sentence
Anagram/Transposition Cipher

Substitution Ciphers

Playfair Cipher
Trifid Cipher
Bifid Cipher
Vigenere Cipher
One Time Pad
Two-square Cipher
Four-square Cipher

First Order Substitution Ciphers

Alphabet Reversal Cipher
Caesar Cipher
Affine Cipher
Book Cipher
Null Cipher

Stream Ciphers

Auto-Key Cipher

Substitution and Transposition Ciphers

ADFGVX Cipher
VIC Cipher

Reasoning

The following section contains the explanations and/or proofs behind the ruled-out ciphers.

Random Sequence of Letters

As part of their work, the students undertaking this project in both 2009 and 2010 conducted surveys of both sober and intoxicated people to see if the letter frequencies obtained were similar to the letter frequencies evident in the Somerton Man's code. Neither of the groups' surveys were consistent with the code and subsequently it was concluded that it is not simply a random bunch of letters. The relevant sections of the previous groups' work can be seen at the following links:

Anagram/Transposition Cipher

By looking at letter frequency plots of various languages against the code, and by identifying other anomalies such as the existence of a 'Q' but no 'U' in the code, the Honours students in 2009 concluded the code did not use a Transposition Cipher alone. The relevant section of their report can be seen here.

Playfair Cipher

The 2009 students concluded that the cipher used was not likely to be the Playfair Cipher based on an empirical test they performed. Their conclusion can be seen here: 2009 Playfair Cipher Conclusion

Vigenere Cipher

The students in 2009 empirically examined the Vigenere Cipher and concluded that it was not likely to have been used. Their summary can be seen here: 2009 Vigenere Cipher Conclusion

One Time Pad

The One-Time pad has been investigated by the 2009 group. They experimented using the Rubaiyat of Omar Khayyam (which is closely linked with the case) and the King James Bible (common at the time) and found no key to de-ciphering the code. Their conclusions can be seen here: 2009 One-Time Pad Conclusion

Alphabet Reversal Cipher

The Alphabet Reversal cipher is a substitution cipher where A becomes Z, B becomes Y, C becomes X etc. This leads to the following encoding and decoding key (read in vertical order):

ABCDEFGHIJKLMNOPQRSTUVWXYZ

ZYXWVUTSRQPONMLKJIHGFEDCBA

Thus, for example, "HELLO" becomes "SVOOL". This cipher was tested on the Tamam Shud code by the 2011 group. A small Java program has been written that takes input from the command line or from a text file and produces output in reversed form. The result of running a file containing the code through the program turns the input of:

MRGOABABD MTBIMPANETP MLIABOAIAQC ITTMTSAMSTGAB

into

NITLZYZYW NGYRNKZMVGK NORZYLZRZJX RGGNGHZNHGTZY

As can be seen, there can be no meaning deciphered from the alphabet-reversed text and thus we can rule out the Alphabet Reversal Cipher as being used in encrypting the Somerton Man's code.

ADFGVX Cipher

The ADFGVX Cipher is a substitution cipher used by German soldiers during WW1 (more information on the cipher available here. We can trivially disprove the use of this cipher by looking at the letter distribution of the Tamam Shud code. The ADFGVX cipher converts messages into a code using only the letters "A,D,F,G,V,X". The Tamam Shud code contains at least 16 different letters of the alphabet, thus we can rule out the ADFGVX cipher and any similar cipher using less than 16 letters.

Affine Cipher

The Affine Cipher is a substitution cipher where each letter is enciphered using a linear formula (ax+b)mod26 where x is a numeric representation of the letter. More information on it can be found here.

The Affine Cipher has been tested by the 2011 students (15/05/2011). Code has been created that cycles through each of the 312 possible combinations for the Affine Cipher, testing each case. The results have been uploaded and can be viewed here. The results do not show any understandable text, and as such, the Affine Cipher has been ruled out.

Two-square Cipher

The Two-square Cipher is similar to the Playfair Cipher in that it is a digraph cipher - it encrypts letters in pairs. This means that the output code should occur in even numbers. In the case of the Somerton Man's code, the lines consist of 9, 11, 11 and 13 letters - no even numbers. This would indicate that a simple digraph encryption technique such as the Two-square Cipher has not been used.

References and useful resources

If you find any useful external links, list them here:

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Cipher Cross-off List

Contents

Purpose