kruger@whyvax.dec.com (Bear with me) (03/17/88)
> Given the source to a program using DES, is it possible to > write a "decrypter" program? > Benjamin Chen > arpa: bchen@wolf.berkeley.edu > uucp: ucbvax!wolf!bchen Based on the discussion that's gone on in the last few weeks, I'd say that first of all, it's not the method that's a mystery. The DES algorithm is well known. Given a small message that is not known to the cryptanalyst, I think everyone agrees the solution is to try all possible keys (not what you're looking for). Finally, there has been some discussion of possible ways of reverse engineering a DES key based on known plaintext. This last has yet to be proved possible though. I believe your question indicated some concept that knowing the method of encryption would allow decryption. In general, this is not true, as generally the only thing that can reliably be kept secret is the key, not the method. Cryptographers assume knowledge of the method when constructing crypto-systems. If you want the full documentation on DES, it is available as a National Bureau of Standards document (FIPS PUB 46 and 81) and is also described in Numerical Recipes dov "If this letter should fall into the hands of any usenet readers, Digital will disavow all knowledge of my actions."