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SUBJECT:  METHOD FOR UPDATING ENCRYPTION KEY INFORMATION IN COMMUNICATION
          UNITS
SOURCE:   MicroPatent via Fulfillment by INDIVIDUAL, Inc.
DATE:     July 6, 1994
INDEX:    [2]
ORDER NO: 402693#
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  MicroPatent via INDIVIDUAL, Inc. : Abstract: Within a communication
system, an encryption controller receives unit identification information
from a plurality of encrypting/decrypting communication units. For any
individual communication unit, the encryption controller uses the unit
identification associated with that transmitting communication unit to
determine if it contains updated encryption key information. If the
transmitting communication unit is not currently updated, a group call is
used to send the current encryption key information to all communication
units within the transmitting communication unit's group, thereby updating
all active, non-current communication units. After a first predetermined
period of time has elapsed, this process is allowed to repeat.

  Ex Claim Text: In a communication system that includes a plurality of
communication units, an encryption controller, wherein the plurality of
communication units includes a first set of communication units that are
currently active and a second set of communication units that are currently
inactive and wherein communication units of the plurality of communication
units readily change from the first set of communication units to the second
set of communication units and vice versa, a method for updating encryption
key information to the plurality of communication units, the method
comprises the steps of: a) transmitting, by a first communication unit in
the first set of communication units, unit identification information to the
encryption controller; b) when the unit identification information is
received, determining, by the encryption controller, that the first
communication unit does not have updated encryption key information; c)
transmitting, by the encryption controller, updated encryption key
information to the plurality of communication units, wherein only the first
set of communication units are updated with the updated encryption key
information; d) initiating, by the encryption controller, a predetermined
wait period; e) changing, by a second communication unit, from the second
set of communication units to the first set of communication units; f) after
expiration of the predetermined wait period, receiving, by the encryption
controller, unit identification information from the second communication
unit; and g) when the unit identification information from the second
communication unit is received, retransmitting, by the encryption
controller, the updated key information to the plurality of communication
units, wherein communication units that have changed from the second set of
communication units to the first set of communication units are updated with
the updated encryption key information.

  Patent Number: 5325432

  Issue Date: 1994 06 28

  Assignee: Motorola, Inc.

  Inventor(s): Gardeck, KevinCutts, Kevin M.

  If you require additional information on this patent, please call
PatentQuery at 800-984-9800.

[07-06-94 at 18:24 EDT, Copyright 1994, MicroPatent, File: m0701215.4pa]