Patent ID: 7647498

Claim:
A method for the authentication of a first and a second device by a third device, the first and the second devices each possessing a shared secret key value h, each of the devices having available to it a public key P selected such that the operation of deriving the secret key value h from the product hP is a computationally difficult operation, the method comprising the steps of: the first device communicating a product R D of a random value r D and P to the second device using the third device, the third device retaining a copy of the product R D ; the second device communicating a product R B of a random value r B and P, and a challenge value e D to the first device using the third device, the third device retaining a copy of the product R B and the challenge value e D ; the first device calculating a value y D defined by a first expression with a value equivalent to the product hP using the random value r D and the challenge value e D , and communicating the value y D and a challenge value e B to the second device using the third device, the third device retaining a copy of the value y D and a challenge value e B ; the second device calculating a value y B defined by a second expression with a value equivalent to the product hP using the challenge value e B and the random value r B and communicating the value y B to the third device; and the third device authenticating the first device and the second device by comparing values of the first expression, the random value r D , the challenge value e D and the value y D , with values of the second expression, the random value r B , the challenge value e B and the value y B .