Patent ID: 8559642

Claim:
A method comprising a first apparatus performing communication operations to communicate with a second apparatus to establish a communication key which is a shared key for communication between the first apparatus and the second apparatus, the first apparatus being a mobile apparatus, wherein a shared key can be generated as being associated with any one of a set of keys available at the mobile apparatus, (wherein the shared key and its associated key may or may not be equal to each other), the set of keys including a current key and one or more previous keys, all said keys being secret keys, said communication operations comprising: (1) receiving, from the second apparatus, key data indicating a key version of a shared key available at the second apparatus, wherein the shared key available at the second apparatus is not transmitted between the mobile apparatus and the second apparatus, wherein all said keys are secret keys; (2) examining the key version, wherein: (2A) if the mobile apparatus determines that the key version corresponds to the current key, then the communication key used by the mobile apparatus is the shared key associated with the current key; (2B) if the mobile apparatus determines that the key version corresponds to a previous key available at the mobile apparatus, then the mobile apparatus uses the shared key associated with the previous key to establish the communication key.