Addressable radio device

1. A method of operating a radio device, the method comprising the radio device:

receiving and processing a radio transmission, wherein the radio transmission includes an address of a second, sending radio device, and wherein the address comprises (i) a value derived from a counter and (ii) a hash of a combination of said value and an identity-resolving key for the sending radio device,

determining that the received hash is a combination of the received value and a stored identity-resolving key associated with the sending radio device; and

determining that the received value satisfies a predetermined freshness condition, wherein the freshness condition includes that the received value is derived from a counter that is greater than a stored local count value associated with the sending radio device.

2. A method of operating a radio device, the method comprising the radio device:

receiving and processing a radio transmission, wherein the radio transmission includes an address of a second, sending radio device, and wherein the address comprises (i) a value derived from a counter and (ii) a hash of a combination of said value and an identity-resolving key for the sending radio device,

determining that the received hash is a combination of the received value and a stored identity-resolving key associated with the sending radio device; and

determining that the received value satisfies a predetermined freshness condition, wherein the freshness condition includes that the received value is derived from a counter that is not more than a freshness threshold amount greater than a local count value associated with the sending radio device.

3. The method of claim 2 , further comprising, after determining that the received value satisfies the predetermined freshness condition, updating the stored local count value to correspond to the counter from which the value in the received address was derived.

4. A radio device configured to:

receive a radio transmission that includes an address of a sending radio device, wherein the address comprises (i) a value derived from a counter and (ii) a hash of a combination of said value and an identity-resolving key for the sending device;

determine that the received hash is a combination of the received value and a stored identity-resolving key associated with the sending radio device; and

determine that the received value satisfies a predetermined freshness condition, wherein the freshness condition includes that the received value is derived from a counter that is greater than a stored local count value associated with the sending radio device.

5. The radio device of claim 4 , configured, after determining that the received value satisfies the predetermined freshness condition, to update the stored local count value to correspond to the counter from which the value in the received address was derived.

6. The radio device of claim 4 , configured to reject a received radio transmission if the radio transmission includes an address of a sending radio device, wherein the address comprises (i) a value derived from a counter and (ii) a hash of a combination of said value and an identity-resolving key for the sending device, and if the received value does not satisfy said predetermined freshness condition.

7. The radio device of claim 4 , wherein said value derived from a counter is 24 bits in length and wherein said hash is 24 bits in length.

8. The radio device of claim 4 , wherein the hash is a function of the output of an Advanced Encryption Standard (AES) encryption of the value derived from the counter, with the identity-resolving key as an encryption key.

9. The radio device of claim 4 , wherein the value derived from a counter is the value of a counter that increments through successive integer values.

10. The radio device of claim 4 , wherein the address is a concatenation of (i) the value derived from a counter and (ii) the hash.

11. The radio device of claim 4 , wherein the stored identity-resolving key is a 128-bit number.

12. The radio device of claim 4 , configured to operate substantially as a Bluetooth Low Energy device.

13. A radio device configured to:

receive a radio transmission that includes an address of a sending radio device, wherein the address comprises (i) a value derived from a counter and (ii) a hash of a combination of said value and an identity-resolving key for the sending device;

determine that the received hash is a combination of the received value and a stored identity-resolving key associated with the sending radio device; and

determine that the received value satisfies a predetermined freshness condition, wherein the freshness condition includes that the received value is derived from a counter that is not more than a freshness threshold amount greater than a local count value associated with the sending radio device.

14. The radio device of claim 13 , configured, after determining that the received value satisfies the predetermined freshness condition, to update the stored local count value to correspond to the counter from which the value in the received address was derived.

15. The radio device of claim 13 , configured to reject a received radio transmission if the radio transmission includes an address of a sending radio device, wherein the address comprises (i) a value derived from a counter and (ii) a hash of a combination of said value and an identity-resolving key for the sending device, and if the received value does not satisfy said predetermined freshness condition.

16. The radio device of claim 13 , wherein said value derived from a counter is 24 bits in length and wherein said hash is 24 bits in length.

17. The radio device of claim 13 , wherein the hash is a function of the output of an Advanced Encryption Standard (AES) encryption of the value derived from the counter, with the identity-resolving key as an encryption key.

18. The radio device of claim 13 , wherein the value derived from a counter is the value of a counter that increments through successive integer values.

19. The radio device of claim 13 , wherein the address is a concatenation of (i) the value derived from a counter and (ii) the hash.

20. The radio device of claim 13 , wherein the stored identity-resolving key is a 128-bit number.

21. The radio device of claim 13 , configured to operate substantially as a Bluetooth Low Energy device.

22. The method of claim 1 , further comprising, after determining that the received value satisfies the predetermined freshness condition, updating the stored local count value to correspond to the counter from which the value in the received address was derived.