Patent ID: 7243232

Claim:
A method of authenticating a pair of correspondents A,B in a data communication system to permit exchange of information therebetween over a communication link, each of said correspondents having a respective private key a,b and a public key p A , p B derived from a generator a and respective ones of said private keys a,b, said method including the steps of i) a first of said correspondents A selecting a first random integer x and exponentiating a function f(α) including said generator to a power g(x) to provide a first exponentiated function f(α) g(x) ; ii) said first correspondent A forwarding to a second correspondent B a message including said first exponentiated function f(α) g(x) ; iii) said correspondent B selecting a second random integer y and exponentiating a function f(α) including said generator to a power g(y) to provide a second exponentiated function f(α) g(y) ; iv) said second correspondent B constructing a session key K from information made public by said first correspondent A and information that is private to said second correspondent B, said session key K also being constructible by said first correspondent A from information made public by B and information that is private to said first correspondent A; v) said second correspondent B generating a value h of a function F[δ,K] where F[δ,K] denotes a cryptographic function applied conjointly to δ and K and where δ is a subset of the public information provided by B thereby to bind the values of δ and K; vi) said second correspondent B forwarding a message to said first correspondent A including said second exponential function f(α) g(y) and said value h of said cryptographic function F[δ,K]; vii) said first correspondent receiving said message and computing a session key K′ from information made public by said second correspondent B and private to said first correspondent A; viii) said first correspondent A computing a value h′ of a cryptographic function F[δ,K′]; ix) comparing said values obtained from said cryptographic functions F to confirm their correspondence; and x) upon such confirmation, permitting further exchange of information over said communication link.