Editing Final Report 2010 (section)

===Verification of Past Algorithms===

Last year’s project group attempted to selectively rule out different possibilities of the code’s meaning in order to get a better idea of what the code is. Specifically, they tested the code against transposition ciphers, tested the code as an initialism as well as several different cipher schemes in both English and other different languages.

One of the tests last year’s group made was to test the possibility of the code being a one-time pad. Using the Somerton Man’s code as the cipher text and segments of the Bible as the cipher key, a resultant undeciphered text was obtained. This was also repeated using each of the poems in the Rubaiyat and for all of these cases, the resultant plaintext revealed no sentences or any English words at all. The resultant output for one of the lines in The Rubaiyat is shown below (the rest can be found [[Media:Past Year Results.rar|here]]).

 Ciphertext:  MTBIMPANETP
 Cipherkey:  ANDLOTHEHUNTEROFTHEEASTHASCAUGHT
 Resultant Plaintext:  ESICAUMGKLK

Given that the cipher key is longer than the ciphertext in each line, each line was independently deciphered as a Vigenere cipher.


Another test last year’s group made use of was [http://en.wikipedia.org/wiki/Markov_chain Markov chains] to determine the probabilities of the code being a certain language or if it used a specific cipher. In relation to this project, the Markov chain<ref>http://en.wikipedia.org/wiki/Markov_chain</ref> models a line of text as a random process where the next character only depends on a fixed number of previous characters in the text. Due to the complexity of these chains, only the first and second order probabilities were calculated using the following equations:

 MP(firstorder) = p(X1)p(X2 | X1)p(X3 | X2)...p(Xn | Xn − 1) 
 MP(secondorder) = p(X1)p(X2 | X1)p(X3 | X2,X1)...p(Xn | Xn − 1,Xn − 2)

For example, the probability of finding the 1st order Markov probability is the probability of getting letter 1, times the probability of getting letter 2 given that the previous letter was letter 1, times the probability of getting letter 3 given that the previous letter was letter 2 and so on.

Because these probabilities are extremely small (of the order 10^-60), the probabilities were normalized using this equation:

 HMMER Score = log2(MP/(1/26)^44)

Where the 1/26^44 represents the probability that each letter of the alphabet has a 1/26 chance of occurring in the 44 positions of the code sequence.

This process was used on various texts in which the Playfair and Vigenere Cipher was implemented. The resultant Markov probabilities were very low and it was determined to be very unlikely that these ciphers were used. This process was also used to obtain Markov probabilities for the code being an initialism of different languages by analysing texts of varying languages. It was determined that the code was most likely to be English if it was an initialism<ref>https://www.eleceng.adelaide.edu.au/personal/dabbott/wiki/index.php/Final_report_2009:_Who_killed_the_Somerton_man%3F#Initial_Letters_of_a_sentence</ref>.

Their results conclude that the Somerton Man’s code is not a one-time pad or a Playfair or Vigenere Cipher, and rather resembles a set of initialisms which may or may not be substituted. From reviewing the previous year's code and attempting to confirm their results, we were able to come to the same conclusion. Based on this, our code attempts to analyse initialisms based in English text and further narrow down what the mystery code could be.