Key fob authentication, retention, and revocation

Abstract

An electronic key fob device, in one embodiment, includes a transmitter, a counter configured to provide a current counter value indicated by a plurality of bits, a memory configured to store an operation key, and a processor coupled to the transmitter and memory. The processor is configured to encrypt the current counter value using the operation key to produce an encrypted counter value, select a subset of the plurality of bits of the current counter value, transmit a message the includes the encrypted counter value and the subset of plurality of bits of the current counter value.

What is claimed is: 
     
         1 . An electronic key fob device, comprising:
 a transmitter;   a counter configured to provide a current counter value indicated by a plurality of bits;   a memory configured to store an operation key; and   a processor coupled to the transmitter and memory, wherein the processor is configured to:
 encrypt the current counter value using the operation key to produce an encrypted counter value; 
 select a subset of the plurality of bits of the current counter value; and 
 transmit a message that includes the encrypted counter value and the subset of plurality of bits of the current counter value. 
   
     
     
         2 . The electronic key fob device of  claim 1 , wherein the counter is a 128-bit counter and the plurality of bits includes 128 bits. 
     
     
         3 . The electronic key fob device of  claim 1 , wherein the processor is configured to, after transmitting the message, increment the counter by one. 
     
     
         4 . The electronic key fob device of  claim 1 , wherein the subset of the plurality of bits of the current counter value is a predetermined number of lowest-order bits of the current counter value. 
     
     
         5 . The electronic key fob device of  claim 4 , wherein the predetermined number of lowest-order bits of the current counter value is 8 bits. 
     
     
         6 . The electronic key fob device of  claim 1 , wherein the processor is configured to use a symmetric encryption type to encrypt the current counter value using the operation key. 
     
     
         7 . The electronic key fob device of  claim 6 , wherein the symmetric encryption type is based on the Advanced Encryption Standard (AES). 
     
     
         8 . The electronic key fob device of  claim 7 , wherein the symmetric encryption type is based on AES-128 encryption. 
     
     
         9 . The electronic key fob device of  claim 8 , wherein the message is associated with a command. 
     
     
         10 . The electronic key fob device of  claim 9 , wherein the command is a request to lock or unlock a vehicle. 
     
     
         11 . The electronic key fob device of  claim 9 , wherein the message further includes a data field that identifies the command. 
     
     
         12 . The electronic key fob device of  claim 9 , wherein the command is a command to cause a control unit paired with the electronic key fob device to enter a revocation mode. 
     
     
         13 . A method comprising:
 receiving a counter value that includes a plurality of bits;   receiving an operation key;   encrypting the counter value using the operation key to produce an encrypted counter value;   selecting a subset of the plurality of bits of the counter value; and   transmitting a message that specifies the encrypted counter value and the subset of the plurality of bits.   
     
     
         14 . The method of  claim 13 , wherein the plurality of bits includes 128 bits. 
     
     
         15 . The method of  claim 13 , wherein the subset of the plurality of bits of the counter value is a predetermined number of lowest-order bits of the counter value. 
     
     
         16 . The method of  claim 15 , wherein the predetermined number of lowest-order bits of the counter value is 8 bits. 
     
     
         17 . The method of  claim 13 , wherein the encrypting of the counter value utilizes a symmetric encryption type. 
     
     
         18 . The method of  claim 17 , wherein the symmetric encryption type is based on the Advanced Encryption Standard (AES). 
     
     
         19 . The method of  claim 18 , wherein the symmetric encryption type is based on AES-128 encryption. 
     
     
         20 . The method of  claim 13 , wherein the message further specifies to whether to lock or unlock a lock.