Hi, I light of recent threads about recognising whether or not a given message/file is encrypted, and using CBW and things along those lines, is there any way to determine how something was encrypted? For example, I know that a statistical analysis of the cyphertext will uncover simple substitution cyphers fairly quickly. Does the same sort of analysis apply to determining whether something was encrypted using IDEA or DES or RSA? I realize that they attempt to maximize the entropy of the cyphertext -- perhaps there is some characteristic amount or range of amounts of entropy associated with these cyphers? Not every package is as nice as PGP in labeling everything it encrypts with headers... Any pointers would be greatly appreciated.... Brendan PS. What I'd like to be able to do is take a given chunk of cyphertext and analyze it and say: "There is an x% probability that this was encrypted using method y...." Hopefully I'd have a reasonable chance of recognizing how it was encrypted, and not all of the percentages would be so low as to make the exercise meaningless.