Method and Apparatus for Encoding Security Status Information
A method of transmitting messages from a sender to a recipient over a wireless channel, the messages including a sequence counter and a frame counter. The method comprises establishing initial values of the sequence counter and the frame counter at the sender. Initial values of the frame counter and the sequence counter are provided to the recipient. The sender sends compressed messages including the value of the sequence counter and not the frame counter and monitors for an acknowledgement of receipt by the recipient. When no acknowledgment is received, the sender sends uncompressed messages until an acknowledgement of receipt is received from the recipient. The sequence counter is incremented and the next value of the frame counter is established as the integer next larger than previous value of the frame counter which is congruent to the sequence counter modulo 256.
1. A method, comprising:
storing a local value of a frame counter of a recipient, wherein the local value of the frame counter was used to encrypt data in a first message;
computing, by at least one hardware processor on a wireless device, a new value of the frame counter from the local value of the recipient and a sequence counter value identifying a second message relative to other messages in a stream of messages;
encrypting, by the at least one hardware processor on the wireless device, data in the second message using a secret key and the new value of the frame counter; and
sending, by the wireless device, the second message to the recipient over a wireless network, the second message including the sequence counter value and the encrypted data.
2. The method of claim 1 , wherein the new value of the frame counter is an integer that is next larger than the local value of the frame counter and congruent to the sequence counter value modulo a specified integer.
3. The method of claim 1 , wherein the sequence counter value comprises a compressed representation of the new value of the frame counter.
4. The method of claim 1 , further comprising: receiving an acknowledgement message from the recipient.
5. The method of claim 4 , wherein the acknowledgment message includes the sequence counter value.
6. The method of claim 1 , wherein sending the new value of the frame counter to the recipient resynchronizes the frame counter with the recipient.
7. A non-transitory computer readable medium storing instructions to cause a processor to perform operations comprising:
storing a local value of a frame counter of a recipient, wherein the local value of the frame counter was used to encrypt data in a first message;
computing, by a wireless device, a new value of the frame counter from the local value of the recipient and a sequence counter value identifying a second message relative to other messages in a stream of messages;
encrypting, by the wireless device, data in the second message using a secret key and the new value of the frame counter; and
sending, by the wireless device, the second message to the recipient over a wireless network, the second message including the sequence counter value and the encrypted data.
8. The non-transitory computer readable medium of claim 7 , wherein the new value of the frame counter is an integer that is next larger than the local value of the frame counter and congruent to the sequence counter value modulo a specified integer.
9. The non-transitory computer readable medium of claim 7 , wherein the sequence counter value comprises a compressed representation of the new value of the frame counter.
10. The non-transitory computer readable medium of claim 7 , the operations further comprising: receiving an acknowledgement message from the recipient.
11. The non-transitory computer readable medium of claim 10 , wherein the acknowledgment message includes the sequence counter value.
12. The non-transitory computer readable medium of claim 7 , wherein sending the new value of the frame counter to the recipient resynchronizes the frame counter with the recipient.