Patent ID: 7240200

Claim:
A system for guaranteeing message integrity, comprising: a distribution center that transmits a transmission including a message and appended values; and a user device that receives said transmission and computes an integrity value K′ that depends on said transmission and at least one stored value, where K′ selectively enables successful further processing of said message if and only if a computed hash value h matches a correct hash value h 1 , guaranteeing the integrity of said message, wherein said appended values include a modulus pq and an authentication value a tat is an encrypted version of an original hash value h 0 , said modulus pq, and a private RSA key z, where s=h 0 z mod pq, wherein said modulus pq is a product of two prime numbers p and q, neither of said prime numbers p and q being separately included in said transmission, wherein said prime numbers p and q are selected by said distribution center such that the likelihood of a product (p−1)(q−1) and an odd-valued correct hash value h 1 of said transmitted message having a greatest common denominator other than 1 is substantially zero, whereby h 1 z=1 mod Φ(pq), where Φ(pq)=(p−1)(q−1), and said correct hash value h 1 is a public RSA key corresponding to said private RSA key z, and wherein said integrity value K′ equals g 1 x g 2 a mod M, where x=s h mod pq, h is a hash value of said message computed by said user device in a similar manner as said correct hash value h 1 , M is a public modulus, a is a stored digital signet, and g 1 and g 2 are preferably unique stored values.