Patent ID: 8543819

Claim:
A method of determining whether protected content stored on a first communication device are accessed by a second communication device, the method comprising the step of: performing a round trip time measurement between the first communication device and the second communication device, said round trip time measurement comprising: transmitting a first signal to the second device at a first time; receiving a second signal from the second device at a second time, generating a third signal using a common secret; determining whether said second signal and said third signal are identical to verify that the second signal was generated using the common secret; generating the round trip time as a difference between said first time and said second time; checking whether the round trip time is within a predefined interval, and allowing access of the protected content provided that the round trip time is within the predefined interval, said second signal and said third signal are identical and the second device is authenticated, wherein: the first device authenticates the second device by: receiving a certificate of said second device; verifying that the certificate of said second device identifies said second device as complying with a set of predefined compliance rules, and the first device securely shares the common secret with the second device according to a key management protocol after having authenticated the second device.