Patent ID: 8051292

Claim:
A method for determining proximity between a first device and a second device, the method comprising: providing a first device storing a first device private key, the first device having an associated secure first device certificate storing secured information, the secured information comprising: a first device public key corresponding to the first device private key; providing a second device storing a second device private key, the second device having an associated secure second device certificate storing secured information, the secured information comprising: a second device public key corresponding to the second device private key; and a second device processing delay; providing a copy of the second device certificate to the first device; establishing a secure authenticated channel between the first device and the second device; sending a first proximity challenge from the first device to the second device, the proximity challenge including a numeric challenge value; receiving the first proximity challenge at the second device, processing the proximity challenge at the second device to produce a response to the first proximity challenge, and sending the response to the first proximity challenge from the second device to the first device; receiving the response to the first proximity challenge at the first device; and performing the following at the first device: verifying, at the first device, that the response to the first proximity challenge is legitimate; determining a gross time between sending the first proximity challenge and receiving the response to the first proximity challenge; subtracting the second device processing delay from the gross time to produce a first net response time; and comparing the first net response time to a first threshold and determining whether the first device and the second device are in proximity based on a result of the comparing.