17 Dec
2003
17 Dec
'03
11:17 p.m.
Marc North writes:
I'm looking for detailed information on a statistical tool to aid in cryptanalysis called an "index of coincidence". I would appreciate it if someone could please explain what this is, how one builds such an index against a given ciphertext, and how it is valuable in the cryptanalysis of said ciphertext.
There is a fairly good general description in "The Codebreakers"; there is also a book by Friedman available from Agean Park Press that covers the topic. I don't know of any public tools to do the work, but it isn't very hard... Perry