Addressable radio device

A short-range radio peripheral device (eg. Bluetooth heart monitor 7 slaved to a mobile phone 3) undergoes secure dynamic address allocation by taking a value derived from a counter and hashing a combination of this value and a stored 128-bit peer Identity Resolving Key (IRK) to produce a resolvable private address for data packets 2. Since each new address is generated by incrementing the counter (eg. every 15 minutes), the master or slave device can distinguish fresh addresses from old addresses, thus indicating a masquerade or mimic attack from peer 11 if an old address (eg. >1 year) is detected. The hash complies with the Advanced Encryption Standard (AES), and the address may comprise the most significant octet of the counter value (ie. a 24-bit count + bits 1 and 0 ) and the least significant octet of the IRK hash (ie. 24-bit hash ).