Progressive Key Tool

This tool converts Progressive Key cipher text into Vigenère/Beaufort/Variant cipher text. The output cipher text can then be used with the solving tool of your choice. While this tool can offer some guidance into what the period of the cipher is, and what reasonable choices for the progression are, it cannot definitively tell you what either are. Expect to have multiple valid period/progression combinations, only one of which is the true value. You may find yourself working several dead ends before finding the correct parameters.

The upper section of the tool helps determine valid period/progression combinations. It takes a period and progression type as input. It displays all possible progression values and the averaged Index of Coincidence of the cipher text that results when the progression is removed. The closer the value is to 0.066, the more likely the combination generates valid English cipher text.

The lower section of the tool performs the conversion of the cipher text into a periodic cipher text (Vigenère/Beaufort/Variant, etc.) based on the type, period and progression selected. This cipher text can be cut-and-pasted into the solving tool of your choice.


Period/Progression Combinations


Cipher Text Conversion