Patent ID: 6226742
Filing Date: 2001-05-01
Classification: H04L

Abstract:
A method of encrypting a plaintext message, P having n+1 blocks (P.sub.i, where n>i>0 and n is an integer), into a ciphertext message such that, in response to contents of the ciphertext message itself, a subsequent violation to integrity of the ciphertext message can be detected, the method comprising the steps of:(a) generating, in response to the plaintext message, an intermediate stream Y, having n+1 blocks (Y.sub.i) with a predefined portion of the intermediate stream defining a message authentication code (MAC) through the steps of:(a1) transforming the plaintext message, through a first predefined cipher block chaining (CBC) operation and using a key formed in response to predefined non-zero integer values a, b, c and d, into the intermediate stream; and(a2) forming the MAC as a predefined portion of the intermediate stream;(a3) wherein the CBC is implemented according to the following so as to yield Y.sub.i :(i) for i=0, as a first function, F, of P.sub.0 as input;(ii) for even i within n, as the function, F, of Y.sub.i-1 and P.sub.i as input; and(iii) for odd i within n, as a second function, G, of Y.sub.i-1 and P.sub.i as input;where: P.sub.0 and P.sub.i represent blocks zero and i within the plaintext message (P), respectively, and the functions F and G comprise terms of the form ax+b and cx+d, respectively, with x representing the input to either of the functions;(b) inserting an encrypted version of the MAC into a predefined portion of the ciphertext message; and(c) generating, in response to the intermediate stream and the encrypted MAC, a remainder of the ciphertext message such that the remainder exhibits a predefined variation contained within the encrypted MAC.