Path: utzoo!mnetor!uunet!seismo!lll-tis!ati.tis.llnl.gov!tjt From: tjt@ati.tis.llnl.gov (Tim Tessin) Newsgroups: sci.crypt Subject: Re: Function needed. Message-ID: <21895@lll-tis.llnl.gov> Date: 14 Dec 87 18:50:46 GMT References: <3523@husc6.harvard.edu> Sender: nobody@tis.llnl.gov Reply-To: tjt@ati.tis.llnl.gov (Tim Tessin) Organization: Lawrence Livermore National Laboratory, Livermore CA Lines: 24 In article <3523@husc6.harvard.edu> siraj@endor.UUCP (Raad Siraj) writes: > I need a function that takes in any variable-length message M of m bits, > and a secret key K of k bits, and produces a fixed length bit pattern of > s bits. The best thing I have found so far is to use DES. It really is not THAT slow, but granted, slower than XOR based algorithms. Procedure: take a 64 bit random seed and feed it thru DES using successive 56 bit chunks of the original message at each pass. Use the 64 bit random number as well as the 64 bit output from the DES munching to create a 128 bit signature. Use an XOR method to eliminate the need for passing twice thru DES to eliminate "meet-in-middle" attacks. Reference: "Digital Signatures ...", Communications of ACM, April 1984 Volume 27, Number 4 The DES algorithm routines were posted to the net a while back by Phil Karn. Tim Tessin - Lawrence Livermore National Laboratory Phone: (415) 423-4560 Net: tjt@ati.tis.llnl.gov (lll-tis.ARPA, lll-tis.UUCP)