Key search and adaptation based on association rules for backward secrecy

Static storage of decryption keys in RFID tags creates a security issue particularly when some of these tags are compromised. To address this problem, a framework is proposed in which these tags search and compute decryption keys based on specific intrinsic association rules embedded in the tags, which feed on publicly known broadcast messages transmitted by the centre. This association rule is nothing but a circular linked list which connects a set of T tokens, in some random order. To facilitate backward secrecy, we also propose a rule adaptation methodology based on random deletions within this circular linked list triggered by random numbers, sent by the centre. We have shown theoretically that the search space for tags in possession of the actual keys is linear in the number of tokens contained in the association rule i.e. O(T ), while the search space for eavesdropping tags increases considerably to O(Tr), where r is centre-defined as the length of the footprint, within a circular linked list. Tradeoffs which involve balancing the extent of backward secrecy with network lifetime, are discussed.