--- Elaine -HFB- Ashton <[EMAIL PROTECTED]> wrote: > Curtis Poe [[EMAIL PROTECTED]] quoth: > *> > *>This probably is not the most helpful comment, but one way to tell > *>if something is encrypted is to compress the data using Archive::Zip > *>or something similar. I don't know, offhand, what the threshhold is, > *>but if a file significantly compresses then either it is unencrypted > *>or has a lousy encryption algorithm. This is because encrypted data > *>should look more or less random and not present patterns which allow > *>compression. > > Rot13 is considered a form of encryption yet merely shifts the > frequency of certain letters. One can also compress the data > before encypting it. There are also a wide range of encyption algorithms > as well as compression tools these days that render that statement untrue. > > e.
Hi Elaine, You are correct, but note where I said "or has a lousy encryption algorithm". Cryptologists, amongst other things, look for patterns in data. If a pattern is spotted, that's a good place to start attacking the cipher and suggests a weakness in the encryption algorithm used. Strong encryption should create an apparently random sequence of characters and thus be very difficult to significantly compress. As for compression tools, if a pattern is spotted, compression algorithms substitute out that pattern with a smaller piece of text. This substitution keeps occuring until no more patterns are spotted (well, sort of). If a compression tool leaves large patterns in the data, it's a poor compression tool. You can read more about this here: http://perl.plover.com/Huffman/huffman.html. I should also add that http://www.perlmonks.org/index.pl?node_id=126891 has an interesting discussion of detecting encrypted data. It should be noted that using compression as a means of detecting encrypted data will not tell you whether the data has been encrypted or compressed. Cheers, Curtis "Ovid" Poe ===== Senior Programmer Onsite! Technology (http://www.onsitetech.com/) "Ovid" on http://www.perlmonks.org/ __________________________________________________ Do You Yahoo!? Send your FREE holiday greetings online! http://greetings.yahoo.com -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
