IDENTIFY UNKNOWN cipher

This tool is based on the Reference Statistics article by the ACA member BION which was published in the May-June 2005 edition of The Cryptogram, the ACA’s bi-monthly magazine.

It uses a number of statistics to determine the best fitness for a cipher to these cipher types and ranks them in order of probability. 

• IC - Index of Coincidence multiplied by 1000.

• Max IC - Maximum Index of Coincidence for periods 1-15, multiplied by 1000.

• Max Kappa - Maximum kappa value for periods 1-15 , multiplied by 1000.

• Digraphic IC - Digraphic Index of Coincidence, multiplied by 10,000.

• Even Digraphic IC - Digraphic IC for even-numbered pairs, multiplied by 10,000.

• 3-char repeats - Square root of the percentage of 3 symbol repeats, multiplied by 1000.

• Odd spaced repeats - Comparison percentage of odd-spaced repeats to all repeats.

• Avg  digraph - ACA member AAHJU’s average log-digraph score.

• Avg  digraph discrep - Average Single letter-Digraph Discrepancy score.

Avg digraph is the average value of the log digraph score using the scores found in ACA member AAHJU’s table from the computer column in the May-June 2001 edition of The Cryptogram. It is based on English language digraph frequencies. 

The most likely cipher type is listed first with the lowest score.