even with plaintext/ciphertext pairs, it has been shown that hundreds of millions of pairs are needed to determine anything about the key involved (DES). I'm sure some of the many responses to your post will include more precise facts. Matt Thomlinson University of Washington, Seattle, Washington. phone: (206) 548-9804 Check my home page -- ftp://ftp.u.washington.edu/public/phantom/home.html PGP 2.2 key available via email, or finger phantom@hardy.u.washington.edu