Hi Alex! I've incorporated your suggestions. Have a look. Marc -- Marc Mutz <Marc@xxxxxxxx> http://marc.mutz.com/Encryption-HOWTO/ University of Bielefeld, Dep. of Mathematics / Dep. of Physics PGP-keyID's: 0xd46ce9ab (RSA), 0x7ae55b9e (DSS/DH)
--- i5/Documentation/Configure.help Mon Sep 25 16:50:54 2000 +++ i5-raidA0-raid1rb15.B2-ext0.0.3a/Documentation/Configure.help Wed Sep 27 23:58:05 2000 @@ -287,22 +287,35 @@ Crypto ciphers CONFIG_CIPHERS - A cipher is a parameter-dependant function E_K that takes a - fixed-length block M (usually 64 or 128 bits) and maps it onto - another (usually equal-sized) block E_K(M) in such a way that, - without knowledge of the "key" K, it is hard to compute - - 1. M, if E_K(M) is given, - - 2. E_K(M), if M is given. - - However, there always exists the inverse function D_K of E_K such - that D_K(E_K(M))=M for any M. M is called the 'plaintext' and E_K(M) - the 'ciphertext'. The ideal cipher is one where it is impossible to - compute M, if you have E_K(M), but not K. In this case, the easiest - way to break the cipher is to use 'brute-force', i.e. try all K in - turn until you hit the right one. With most ciphers in this library, - K is a 128-bit number. Here, brute-force attacks are infeasible. + Ciphers basically help us scramble data so that other people don't + get access to it. Useful applications for this include hiding hard + drive contents or network traffic from unauthorized eyes. Compare a + file encrypted with a cipher with very good safe: The document is in + it, you can carry the document with you (if the safe is not too + heavy), but others can steal it, too. However, they will not be able + to read the document if the safe is any good. + + Mathematically speaking, a cipher is a parameter-dependant function + E(K, ) that takes a fixed-length block M (usually 64 or 128 bits) + and maps it onto another (usually equal-sized) block C=E(K,M) in such + a way that, without knowledge of the "key" K, it is hard to compute + + 1. M, if C and the function E are given, + + 2. C, if M is given and the function E is known. + + M is called the 'plaintext' and C the 'ciphertext'. The above + properties are commonly described as "All the security of the cipher + lies in its key". However, there always exists the inverse function + D(K, ) of E(K, ) such that D(K,E(K,M))=M for any M. The ideal + cipher is one where it is impossible to compute M if you have C, but + not K. In this case, the easiest way to break the cipher is to use + 'brute-force', i.e. try all K in turn until you hit the right + one. With most ciphers in this library, K is a 128-bit number. Here, + brute-force attacks are infeasible since they require testing all + 2^128 possible keys K, which would take far too long on any + conceivable computer (some big multiple of the age of the universe + for example). Unfortunately, the ideal cipher has not been found yet, so most ciphers in this library, or certain 'reduced-round' versions
