Method of rekeying roaming communication units

• US 5,471,532 A
• Filed: 02/15/1994
• Issued: 11/28/1995
• Est. Priority Date: 02/15/1994
• Status: Expired due to Term

• Current Assignee: Brass, Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Green, David A., Gardeck, Kevin, Cutts, Kevin
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US08/196,352
• Time in Patent Office: 651 Days
• Field of Search: 380/21, 380/23
• US Class Current: 380/272
• CPC Class Codes: H04L 2463/062 applying encryption of the keys cryptographic mechanisms or cryptographic arrangements for key distribution using key encryption key H04L9/0822
• CPC Class Codes: H04L 9/0822 using key encryption key
• CPC Class Codes: H04L 9/083 involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying
• CPC Class Codes: H04W 12/0433 Key management protocols

Abstract

A method of providing over the air rekeying information to roaming communication units in a secure wide area communications system including a home key unit 101, a first key unit 102, and second key unit 103 operably linked together. A communication unit 104 affiliated to the home key unit 101 roams to the locality of the first key unit 102. The roaming communication unit then transmits a key request 112 to the first key unit 102 that transmits a unit information request 108 to the home key unit 101. The home key unit 101 responds by transmitting a rekey information packet 109, that includes a unit key 110, to the first key unit 102. The first key unit 102 then transmits a key information packet 113, that includes the unit key 110, to the roaming communication unit. The roaming communication unit then uses the unit key 110 to communicate securely at the locality of the first key unit.

Claims

1. In a communication system including a home key unit with an associated home coverage area, a first key unit with an associated first coverage area, a second key unit with an associated second coverage area, and including a communication unit that may roam from the home coverage area to the first coverage area or the second coverage area, a method for over-the-air rekeying of the roaming communication unit as it roams from the home coverage area, the method comprising the steps of:

a) after entering the first coverage area, transmitting, by the roaming communication unit, a key request to the first key unit, wherein the key request includes a communication unit identification code for the roaming communication unit, a home identification code, and a request for a key;

b) transmitting, by the first key unit, a unit information request to the home key unit, wherein the home key unit is affiliated with a system identified by the home identification code, the unit information request including the communication unit identification code, the home key unit identification code, and the request for a key;

c) transmitting, by the home key unit, a rekeying information packet to the first key unit; and

d) transmitting, by the first key unit, a key information packet to the roaming communication unit.

2. In the method of claim 1, step (c) further comprises encrypting the re-keying information packet, by the home key unit, prior to transmitting.

3. In the method of claim 1, when multiple key units receive the key request, step (b) further comprises determining by a predetermined priority, which of the multiple key units will transmit the unit information request to the home key unit.

4. The method of claim 1, further comprises the steps of:

transmitting, by the roaming communication unit, the key request to a second key unit;

upon receipt of the key request, transmitting, by the second key unit, a second unit information request to the home key unit; and

transmitting, by the second key unit, a subsequent key information packet to the roaming communication unit, based upon a response to the second unit information request.

5. In the method of claim 1, step (c), wherein the rekeying information packet further comprises at least a unit key and a status message, wherein the status message includes at least one of an inhibit rekeying, enable rekeying and clear keys.

6. In a communication unit including a home key unit with an associated home coverage area, a first key unit with an associated first coverage area, and including a communication unit that may roam from the home coverage area to the first coverage area, a method for over-the-air rekeying of the roaming communication unit after it has left the home coverage area and has entered the first coverage area, the method comprising the steps of:

a) transmitting, by the home key unit, a rekeying information packet of the roaming communication unit to the first key unit, wherein the rekeying information packet comprises a unit key and a status message, the status message including at least one of an inhibit rekeying, enable rekeying and clear keys;

b) storing, by the first key unit, the rekeying information packet, wherein the rekeying information packet includes at least a portion of a key information packet;

c) determining, by the first key unit, when to transmit the key information packet to the roaming communication unit; and

d) transmitting, by the first key unit, the key information packet to the roaming communication unit.

7. In the method of claim 6, step (a) further comprises encrypting the rekeying information packet, by the home key unit, prior to transmitting.

8. In the method of claim 6, step (c) further comprises receiving, by the first key unit, at least a push-to-talk.

9. In the method of claim 6, step (c) further comprises receiving, by the first key unit, at least a key request.

10. In the method of claim 6, step (c) further comprises receiving, by the first key unit, at least knowledge of the presence of the communication unit at a site.