Patent ID: 6711680
Filing Date: 2004-03-23
Classification: G06Q,G07B,H04L

Abstract:
A method for generating a first message and verifying that a variable used in the generation of said first message is between a predetermined upper limit and predetermined lower limit, said method comprising the steps of:providing a trapdoor function R to a message originator and to a message verifier, said trapdoor function R having a corresponding inverse function Râˆ’1 that is maintained in secrecy by a third party; determining an integer K equal to the difference between said upper limit and said lower limit; providing a second message including Râˆ’K(T) from said third party to said message originator, wherein T is a value within a range of said trapdoor function R; generating, at said message originator, a third message Sx=Rx(Râˆ’K(T)), wherein x is an integer equal to the absolute value of the difference between a current value of said variable and a first one of said upper limit and said lower limit; incorporating at least said third message Sx into said first messages; receiving, at said message verifier, said first message, said message verifier recovering from said first message said third message Sx, said message verifier further determining said current value of said variable and a second one of said upper limit and said lower limit; and confirming that Ry(Sx)=T, wherein y is an integer equal to the absolute value of the difference between said current value of said variable and said second one of said upper limit and said lower limit.