Patent ID: 6128737
Filing Date: 2000-10-03
Classification: H04L

Abstract:
A method of generating a message authentication code (MAC) from a plaintext message (P) having n+1 blocks (P.sub.i ; where n.gtoreq.i.gtoreq.0 and n is an integer) comprising the steps of:transforming the plaintext message, through a cipher block chaining (CBC) operation and using a key formed in response to predefined non-zero integer values a, b, c and d, into a first stream Y having n+1 blocks (Y.sub.i); andforming the MAC as a predefined portion of the first stream;wherein the CBC is implemented according to the following so as to yield Y.sub.i :(a) for i=0, as a first function, F, of P.sub.0 as input;(b) for even i within n, as the function, F, of Y.sub.i-1 and P.sub.i as input; and(c) 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.