The following set of cryptanalytic tools is based on the GW BASIC code in appendix F of this declassified Basic Cryptanalysis field manual.
Ciphertext:
Monographic IC:
Digraphic IC:
Length of text:
For frequency analysis, please use the improved frequency analysis tool.
The above ciphertext with repeated sequences underlined.
Periodic Index of Coincidence for a period length of (change for different period)
If the average periodic IC is high, then the chosen period length is likely to be correct, or a multiple of the correct period length. This analysis is helpful for determining the keyword length if a periodic key encryption system like Vigenere Cipher is in use.
Monographic Index of Coincidence - a measure of the likelihood that this ciphertext is a letter-for-letter substitution.
Digraphic Index of Coincidence - a measure of the likelihood that this ciphertext uses two letters to represent one plaintext character.