Letters frequency analysis for ciphers :
Frequency analysis is a commonly used technique in domain such as cryptanalysis. The most ancient description for what we know was made by Al-Kindi,
dating back to
the IXth century. The letters frequency analysis was made to decrypt ciphers such as monoalphabetical ciphers, for instance
Caesar cipher, which means that letters frequency analysis could have been used before Al-Kindi.
This tool allows you to analyse cipher letters in any text/cipher you want. It counts all the letters, digraphs, trigraphs and quadrigraphs and print a chart
with
all the data. Once you got the frequency for each letter (or digraphs, trigraphs, quadrigraphs), you have to compare it to language letters frequency. In the
options you can print a chart with different languages letters frequencies, if I have the data. If I don't have the frequencies, try to search for it on
internet. For now I have frequencies charts for english, french, german, italian, spanish and portuguese.
On the options you also can include into the frequency analysis all the caracters or only the numbers. When you try to decrypt a cipher using this tool,
keep in mind that your text may be too short to really find a pertinent frequency analysis, you should then try to compare it with different letters. For
instance in english the letters that you'll find the most are e, t, a ,o, i, n. If your cipher frequencies are for instance h, d, w, q, l, u, try to match h
with
e, d with t, w with a, q with l, u with n. It will not be a good match if your cipher was too short, so then try another match, for instance d for a instead
of t, try different things until you find the good match.
