On 1 Jun 96 at 19:13, anonymous-remailer@shell.port wrote: [..]
But then you still have the problem of identifying the contents. If there were no headers, one could not tell if the message was compressed using ZIP, LHA, StuffIt, tar*, compress, gzip, Alice's Magical Supercompressor, or even if it was left alone. One could also not tell if the decryption happened successfully.
Actually you could, since the actual encoding isn't random. It means something to the compressor. And if you know something about compression algorithms you could probably make some good estimates. (I've seen some arguments that bit-wise a compressed file is easier to make a known plaintext attack against than an uncompressed text file...) Try taking various small (but compressable) text files that are different and run them through compressors. Ignore the usual compressor header information and look at a hex dump of the compressed data... think about it in terms of bits. Look at the algorithm that encoded the data. A good way to avoid known plaintext is to use a feedback mode with a random IV (from a good RNG!). Not perfect, of course... Rob. --- No-frills sig. Befriend my mail filter by sending a message with the subject "send help" Key-ID: 5D3F2E99 1996/04/22 wlkngowl@unix.asb.com (root@magneto) AB1F4831 1993/05/10 Deranged Mutant <wlkngowl@unix.asb.com> Send a message with the subject "send pgp-key" for a copy of my key.