Dynamic encryption key selection for encrypted radio transmissions

• US 5,222,137 A
• Filed: 04/03/1991
• Issued: 06/22/1993
• Est. Priority Date: 04/03/1991
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: O'Connor, James M., Laird, Kevin M., Barrett, Steven T., Murray, Richard E.
• Primary Examiner(s): SWANN, TOD R
• Application Number:
  US07/680,188
• Time in Patent Office: 811 Days
• Field of Search: 380/21, 380/43, 380/46, 380/44, 380/49
• US Class Current: 380/271
• CPC Class Codes: H04L 2209/80 Wireless
• CPC Class Codes: H04L 9/0894 Escrow, recovery or storing of secret information, e.g. secret key escrow or cryptographic key storage
• CPC Class Codes: H04L 9/16 the keys or algorithms being changed during operation

Abstract

A radio (100) transmits and receives encrypted signals having unencrypted key identifiers, allowing other radios having the corresponding key identifiers and encryption keys to communicate with radio (100). Prior to transmitting an encrypted message, radio (100) selects a unique key identifier automatically and uses the corresponding encryption key to encrypt the message that will be transmitted. Radio (100) transmits the key identifier in an unencrypted format with the encrypted message in order to allow other radios to determine the encryption key used in encrypting the message. When receiving an encrypted message, radio (100) uses the predetermined process stored in the radio (100) to properly select the proper encryption key for use in decrypting the incoming message.

Claims

1. A method for transmitting encrypted messages between first and second radios, each of the radios including a plurality of encryption keys each having a unique key identifier, each of the first and second radios also each having an encryption key selection program, the method comprising the steps of:

at the first radio;

selecting a key identifier from among the plurality of key identifiers;

encrypting a message that is to be transmitted to the second radio using the encryption key which corresponds to the selected key identifier;

appending the key identifier to the encrypted message;

transmitting the encrypted message and key identifier to the second radio;

selecting from among the plurality of encryption keys a new encryption key using the encryption selection program found in the first radio;

at the second radio;

receiving the encrypted message from the first radio;

decoding the key identifier sent with the encrypted message;

decrypting the encrypted message using the encryption key which corresponds to the decoded key identifier; and

selecting a new encryption key using the encryption selection program found in the second radio which matches the new encryption key selected by the first radio.

2. A method for transmitting encrypted messages as defined in claim 1, further comprising the steps of:

at the second radio;

encrypting a message to be transmitted to the first radio using the new encryption key selected by the encryption selection program found in the second radio; and

at the first radio;

decrypting the encrypted message sent by the second radio using the new encryption key selected by the encryption selection program found in the first radio.

3. A method for transmitting encrypted messages as defined in claim 1, wherein the selected key identifier is transmitted in an unencrypted format with the encrypted message that is transmitted to the second radio.

4. A method for transmitting encrypted messages as defined in claim 1, wherein the key identifier selected by the first radio is randomly selected from among the plurality of encryption keys found in the first radio.

5. A method for transmitting encrypted messages as defined in claim 4;

wherein the new encryption key selected using the encryption selection program found in the first radio is dependent on the randomly selected key identifier.