Patent ID: 8503677

Claim:
A communication device comprising: a receiver for receiving a secure communication frame from another communication device, the received secure communication frame including received identifying information and a received time varying parameter, the received secure communication frame having been generated by a security transform performed on at least the received time varying parameter; a history manager for maintaining received authentication history information and performing a first freshness test by searching for the received identifying information in the received authentication history information, the first freshness test failing if the received identifying information is found in the received authentication history information and passing if the received identifying information is not found in the received authentication history information; a time varying parameter manager for maintaining a local time varying parameter and a margin, and performing a second freshness test by comparing the received time varying parameter with the local time varying parameter, the second freshness test failing if the received time varying parameter is older than the local time varying parameter by more than the margin, and passing if the received time varying parameter is not older than the local time varying parameter by more than the margin; an authentication key manager for managing an authentication key related to the security transform; and an authentication processor for using the authentication key to authenticate the received secure communication frame when the first freshness test and the second freshness test both pass, the received secure communication frame being discarded without authentication if either the first or second freshness test fails.