United States Patent c191
`Barrett et al.
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US005199069A
`5,199,069
`[11) Patent Number:
`[45) Date of Patent: Mar. 30, 1993
`
`[54) AUTOMATIC ENCRYPTION SELECTOR
`[75)
`Inventors: Steven T. Barrett, Plantation; Bruce
`D. Oberlies, Coral Springs, both of
`Fla.
`[73) Assignee: Motorola, Inc., Schaumburg, Ill.
`[21) Appl. No.: 660,186
`[22] Filed:
`Feb. 25, 1991
`[51]
`Int. Cl.' ......................... H04K 1/00; H04K 9/00;
`H04L 9/02
`[52) U.S. CI •........................................ 380/28; 380/21;
`380/47; 380/2
`[58) Field of Search ...................... 380/28, 47, 21, 1, 2
`[56)
`References Cited
`U.S. PATENT DOCUMENTS
`4,819,267 4/1989 Cargile et al ......................... 380/23
`4,914,697 4/1990 Dabbish et al ........................ 380/28
`
`5,091,938 2/1992 Thompson et al .................... 380/21
`
`Primary Examiner-Stephen C. Buczinski
`Attorney, Agent, or Firm-Pedro P. Hernandez
`
`[57)
`ABSTRACT
`A radio (100) capable of automatically. selecting an
`encryption algorithm from among a plurality of algo(cid:173)
`rithms (122 and 124) is disclosed. The method for auto(cid:173)
`matically selecting the proper encryption hybrid in(cid:173)
`cludes the steps of: attempting to decrypt the encrypted
`signal with one of the plurality of encryption algo(cid:173)
`rithms; determining if the encryption algorithm used to
`decrypt the encrypted signal matches the encryption
`algorithm used by the encrypted signal; and developing
`a control signal upon the proper matching of the en(cid:173)
`cryption algorithms.
`
`6 Claims, 5 Drawing Sheets
`
`160
`
`162
`
`118
`
`17.
`
`164
`
`INTERFACE
`AND
`CONTROL
`
`166 144
`I
`I
`146
`
`168
`
`HYBRID
`f 1
`
`HYBRID
`f 2
`
`170
`
`122
`
`158
`
`\
`120
`
`116
`
`/
`
`140
`
`138
`
`/
`
`142
`
`112
`
`114
`
`CONTROLLER
`
`128
`
`106
`
`128
`
`/
`
`RADIO
`CONTROLLER
`
`ANTENNA
`SWITCH
`
`136
`\
`
`lc:8
`
`/
`RECEIVER
`
`130
`
`100
`
`IPR2016-01710
`UNIFIED EX1017
`
`

`
`....
`\C
`\C
`~
`....
`U1
`
`Q °' \C
`
`Cl'I
`
`""' s,
`00 =-!
`
`~
`~
`~
`a:
`
`~ a (1) a
`0 • 00. •
`
`134
`\
`
`\
`12t
`
`!--.....13(.
`
`----
`
`,_
`
`· SWITCH
`ANTENNA
`I
`I
`104
`
`I.-
`
`RECEIVER
`
`100
`
`/
`
`'
`
`\
`136
`
`110
`
`\.
`
`132
`
`CONTROLLER
`
`RADIO
`
`-
`
`'
`
`128
`
`/
`
`y 106
`
`128
`
`~ -l TRANSMITTER
`138
`/"
`
`FIG.1
`
`100
`
`-
`
`, I
`114
`
`'
`
`~
`
`I _
`
`I
`I
`150 148
`
`-CONTROLLER
`
`154 156
`
`\ \
`
`\
`
`--
`
`120
`\
`
`158
`
`\
`
`152 DECODER
`\
`
`122
`\
`\
`#2
`
`-HYBRID
`
`
`-.
`
`124
`/
`
`i....., HYBRID
`
`#1
`
`/170
`
`\
`
`112
`
`/
`
`140
`
`.
`
`142"
`
`168,
`
`1 l
`
`CONTROL
`INTERFACE /
`
`AND
`
`116 /
`
`•
`
`172/
`
`146
`I
`\
`166 144
`\
`
`118
`
`/
`
`. DIA
`AID
`!
`
`164
`\
`
`\
`
`1~2
`
`160,
`
`

`
`U.S. Patent
`
`Mar. 30, 1993
`
`Sheet 2 of 5
`
`5,199,069
`
`FIG.2
`
`NO
`
`204
`
`206
`
`BEGIN LOOKING
`FOR SYNCH
`DETECT
`
`YES
`
`212 \
`
`SYAY WITH
`SELECTED
`HYBRID UNTIL
`END OF CALL
`
`,_---.. ___ /
`
`210
`
`SWITCH
`HYBRIDS .______,
`
`EXIT
`
`

`
`U.S. Patent
`
`Mar. 30, 1993
`
`Sheet 3 of 5
`
`5,199,069
`
`FIG.3
`
`START
`
`304
`
`306
`
`GET RX
`HANGTIME
`
`YES
`
`YES
`
`SELECT
`DEFAULT
`HYBRID
`
`312
`
`.EXIT
`
`DECREMENT
`,.--------. RX HANGTIME
`TIMER
`
`NO
`
`/324
`
`----
`
`320 . . RESET RX
`YES
`/
`..-------
`HANG TIME
`TIMER
`SELECT
`DEFAULT
`HYBRID
`
`322
`'
`
`EXIT
`
`

`
`U.S. Patent
`
`Mar. 30, 1993
`
`Sheet 4 of 5
`
`5,199,069
`
`FIG.4
`
`START
`
`NO
`
`SET RX
`HANGTIME=O
`RESELECT DEFAULT
`HYBRID
`
`404 \
`
`PROCESS PTT
`NORMALY
`USING SELECTED
`HYBRID
`
`EXIT
`
`/
`
`406
`
`

`
`U.S. Patent
`
`Mar. 30, 1993
`
`Sheet 5 of 5
`
`5,199,069
`
`START
`
`YES
`
`516
`
`LOAD TRANSMIT
`HANGTIME DELAY
`TIMER
`
`506
`
`DECREMENT
`TIMER
`
`510
`\
`RESET
`TIMER
`
`YES
`
`512
`
`NO
`/
`
`NO
`
`YES
`
`514
`
`EXIT
`
`FIG.5
`
`

`
`1
`
`5,199,069
`
`AUTOMATIC ENCRYYTION SELECTOR
`
`TECHNICAL FIELD
`This invention relates to digitally encoded communi(cid:173)
`cation signals, and more specifically to a method and
`means for automatically selecting an encryption algo(cid:173)
`rithm.
`
`2
`different users or user groups. For example, a supervi(cid:173)
`sor may wish .to receive transmissions from a group of
`users using one type of encryption algorithm (i.e. DVP(cid:173)
`XL TM, trademark of Motorola, Inc.) and also be able
`S to receive messages on the same channel from another
`group of users using another encryption algorithm (i.e.
`DES-XL TM, trademark of Motorola, Inc.). Presently,
`the only way a user could receive the messages from the
`two different groups is to manually switch the encryp-
`BACKGROUND
`10 tion algorithm on the radio, or else the radio would miss
`one of the messages assuming the radio had one specific
`Communications between radio communication de-
`vices such as portable radios, mobiles, and fixed equip-
`algorithm selected. Each of the different encryption
`algorithms on the radio can also carry a plurality of
`ment are readily susceptible to interception by eaves-
`encryption keys, the radio can automatically choose
`droppers. If security of communications is important to
`it can be 15 among different keys of a particular encryption algo-
`radio communication equipment users,
`achieved with a system such as the Motorola Digital
`rithm by using the technique described in U.S. Pat. No.
`4 440 976 Th
`Voice Protection System. This is a system that converts
`· ·
`ted b
`if
`~
`.
`.
`.
`.
`. .
`.
`,
`,
`.
`e patent IS mcorpora
`. y re1erence as
`an analog co~umcation si~al mto a digital bit stream
`set forth fully herein. This patent describes how to
`~r use of,~ con~mll:ousl~-variable-slope delta modll;1a~or 20
`automatically pick from a group of keys belonging to
`( CVSD ) which IS a bit synchronous analog to digital
`ifi
`ti.
`al
`·thm ("
`· DES
`·
`hni
`Th d' 'tal b'
`. h
`one spec c encryp on
`gon
`i.e. usmg
`-
`· kin
`XL TM
`igi
`it stream IS t en
`d
`f dif
`1 alit
`ti
`conversion tee
`que.
`e
`fi
`g rom a P ur Y 0
`encryp on an pie
`scrambled (encrypted) by a system to which only the
`-
`sender and authorized receivers are given "keys" which
`ferent keys).
`.
`.
`allow the signal to be decrypted. When such a system is
`A need however .exists m the. art for a meth?<i and
`in use, the eavesdropper may detect the signals, but he 25 means ~or auto~atically selectmg between different
`encryption algonthms (e.g. betwee~ DES-XL TM ~d
`receives no more than a pseudorandom signal resem-
`bling noise since he lacks the means to decrypt the
`DVP-XL TM , etc.). For example, different encryption
`signals.
`'
`algorithms such as DVP-XL TM , and DES-XL TM
`The user of a two-way radio having a digital encryp-
`could be utilized in one radio and the ability of automat-
`- tion system such as the Motorola Digital Voice Protec- 30 ically selecting the correct algorithm to use in order to .
`tion System needs to be able to receive both "clear"
`decrypt an incoming signal would be very useful espe-
`(non-encrypted) communication messages, and en-
`cially for supervisory radios which need to communi-
`cate with groups of radios utilizing different encryption
`crypted binary form messages since a radio user wants
`to be able to receive both clear or encrypted messages
`algorithms.
`automatically. The detection of the presence of digital 35
`SUMMARY OF THE INVENTION
`signals can be carried out by a system such as that of
`U.S. Pat. No. 3,995,225. The patent is incorporated by
`This method and means is capable of automatically
`selecting a proper algorithm from among a plurality of
`reference as if set forth fully within.
`different algorithms. In one aspect of the invention, a
`If the receiver circuitry has detected the presence of
`~ encrypted signal, i~ is next nCCCSS;811' to. submit the 40 radio includes the capability of automatically choosing
`signal to an un.scrambling proc:ess. This reqwr~ t~at the
`a algorithm which properly decrypts the encrypted
`user have av~able a ~ecryptmg sy~tem con~g the
`signal. The radio checks among a plurality of algo-
`same encIYJ?tion alg~nt~ (encryption algonthm refers
`rithms in order to find the algorithm which matches the
`to an algonthm which lS used to . decrypt o: encrrpt
`algorithm that was used to encrypt the digital signal. In
`encrypted messages) and the specific ke.y with which 45 another aspect of the invention, a method for automati-
`the message was encrypted. If ~e radio has such a
`cally selecting from among a plurality of different algo-
`system, and the m~ge was applied to the .system the
`rithms includes the steps of: attempting to decrypt the
`c osen °
`encrypted message will be decrypted and will be heard
`ted ·gnal· d te
`· ·
`ifth al
`·thm h
`t
`' e ~g e gon
`as ordinary voice and/or data at the communication
`encryp
`si
`device receiving the message. If the user did not have so decrypt the en~rypted signal has properly deci;:pted
`the encrypted signal; an~ developmg a control Signal
`the proper encryption algorithm and specific key the
`once a the encrypted Signal has been properly de-
`result would be to produce a signal with noise-like
`properties, which would be unintelligible. A decrypted
`crypted.
`signal can be distingllished from a signal that has not
`BRIEF DESCRIPTION OF THE ORA WINGS
`been decrypted by a circuit such as the one in U.S. Pat. 55
`No. 4,197,502. This patent is incorporated by reference
`FIG. 1 is a block diagram of a radio utilizing the
`present invention.
`as if set forth fully herein. The circuit of that patent
`FIG. 2 is a flowchart of th~ ope~tion ?fthe radio of
`provides a signal which can be used to mute a receiver
`if a digital signal has not been decoded.
`FIG. 1 w~en an encrypted si~ IS received.
`FIG. 3 IS a flowc?-rt showing ~e ste.ps that occur
`In a typical encrypted communication system, groups 60
`after the encrypted signal has termmated m accordance
`of portable radios or mobile units communicate with
`.
`with the present invention.
`each other using the same encryption algorithms, hav-
`FIG. 4 is a flowchart showing the steps that occur
`ing the same specific algorithm keys. Frequently it is
`anytime the radio push to talk switch is pressed in ac-
`desirable for supervisory radios to be able to listen to
`different groups of users with each group having their 65 cordance with the present invention.
`FIG. 5 is a flowchart showing the steps that occur
`own different encryption algorithms. A supervisor, for
`example, might wish to receive and talk back to scram-
`after the radio push to talk switch is released in accor-
`bled messages coming in on one specific channel from
`dance with the present invention.
`
`

`
`5,199,069
`
`4
`3
`made using the encryption algorithm residing in hybrid
`DETAILED DESCRIPTION OF THE
`124 (i.e. DES-XL) to decode the encrypted digital sig(cid:173)
`PREFERRED EMBODIMENT
`nal. If it is determined .by hybrid 124 that the same
`algorithm that was used to encrypt the incoming digital
`Referring now by characters of reference to the
`drawings and first to FIG. 1, a block diagram of a radio s signals resides in hybrid 124, in this case DES-XL, then
`100 utilizing the present invention is shown. The radio
`hybrid 124 sends out a control signal. In this particular
`100 consists of a conventional transmitter 106 and con-
`case since the hybrid uses DES-XL algorithm the con-
`ventional receiver 108 selectively coupled to an antenna
`trol signal is an "in synch message" via the hybrid synch
`102 via antenna switch 104. Microphone 128 is coupled
`line 150 to controller 114.
`to transmitter 106 in order to con'(lert voice signals to 10
`The DEX-XL algorithm and other Motorola, Inc.
`electrical signals which can be acted upon by transmit-
`''XL" algorithms use a type of encryption known in the
`ter 106. Transmitter 106 then transmits radio frequency
`art as output feedback which is a self synchronizing
`(R.F.) signals via line 128 to antenna switch 104 which
`serial process which determines that a correct decryp-
`in turn routes the R.F. signal to antenna 102. Receiver
`tion of a signal has occurred when synchronization is
`108 receives incoming R.F. signals via line 130 and IS achieved between the encrypted message and the de-
`presents these signals as voice messages via line 134 to
`cryption algorithm which is what determines that the
`speaker 126. Preferably radio 100 is controlled by radio
`encrypted signal has been properly decrypted, and a
`controller 110 which can be any one of a number of
`proper control signal is then generated by the hybrid
`conventional microprocessors known in the art prefera-
`124. The means for developing the control signal in this
`bly having onboard memory and I/O capabilities. 20 case is accomplished by generating an output signal
`(either high or low voltage level on one of the I/O lines
`Radio controller 110 controls the overall operation of
`radio 100. Radio controller 110 controls antenna switch
`of bus 150) once the algorithm in hybrid 124 becomes in
`104 via line 132 in order to automatically route out-
`synch to the encrypted signal. For other types of algo-
`bound/inbound messages to both transmitter 106 and
`rithms (i.e. non-XL types of algorithms) such as algo-
`receiver 108. Also part of the present invention is con- 2S rithms using cipher feedback techniques other methods
`of generating a valid output signal as known in the art
`troller 114 which acts as the controller for the overall
`encryption circuit operation. Controller 114 is coupled
`can be utilized to inform that a proper decryption has
`to radio controller 110 via address/data bus 112 which
`been achieved.
`allows both controllers 110 and 114 to communicate
`If the in synch message is received, controller 114
`with each other. Controller 114 is also coupled to the 30 knows that the proper encryption algorithm (hybrid) is
`interface and control 116 circuit and CVSD converter
`being used to decrypt the incoming signal. On the other
`118 via data/address buses 142, and 140 respectively.
`hand, if the in synch message is not received within a
`Bus 166 is used to exchange control information be-
`certain period of time, the controller 114 will automati-
`tween CVSD converter 118 and interface and control
`cally send a signal via line 156 to decoder 120 in order
`circuit 116.
`3S to switch the currently selected data bus from bus 152
`In order to better understand the present invention,
`to data bus 158 (hybrid 124 to hybrid 122).
`the reception of an encrypted message by radio 100 will
`Decoder 120 is a multiplexer which controls buses
`first be considered, and also the process involved in
`152 and 158 in order to select one of the two buses in
`order to carry data from the· seleeted hybrid (122 or
`decoding the incoming encrypted message. Once a mes-
`sage (signal) is received by receiver 108, the signal is 40 124) to controller 114 via bus 154. Data such as key
`recovered by the receiver discriminator circuitry and
`information, write enable signals, etc. are carried be-
`routed to the interface and control circuitry 116 via line
`tween the hybrids and controller 114. Decoder 120 also
`136, interface and control circuit 116 then determines if
`routes signals from hybrids 122 and 124 to the interface
`the signal is encrypted or clear (non-encrypted). If the
`and control circuit 116 via bus 168, and also to the
`signal is determined to be encrypted, the signal is syn- 4S CVSD converter 118 via bus 170 when required. De-
`coder 120 is switched by controller 114 which controls
`chronized with a clock recovery circuit found in the
`interface and control circuit 116 which in turn synchro-
`the routing of signals through decoder 120. Controller
`nizes a free-running receiver clock circuit which is part
`114 informs the interface and control circuit 116 of any
`of receiver 108 in order to synchronize the incoming
`hybrid change in order for it to know that a new hybrid
`signal. Part of interface and control circuit 116 includes SO has been selected. Again, an "in synch message" is
`looked for coming from line 148 at controller 114. If the
`a data regeneration circuit which reshapes the signal
`into a 12 Kbit/second binary signal (the same signal that
`incoming signal does not match any of the encryption
`left the encryption encoder of the transmitting radio).
`hybrids in radio 100 the controller 114 will stop the
`The binary signal is then sent to the encryption by-
`hybrid selection process and return to the previously
`brid (124 or 122) which had been previously selected by SS selected default hybrid.
`Assuming that an "in synch message" (control signal)
`the user (as by the conventional operation of a switch
`on the radio). Encryption hybrids 122 or 124 are en-
`is detected coming from hybrid 122, then hybrid 122
`cryption circuits, and in particular, they are circuits
`remains selected in order to decrypt the incoming bi-
`capable of storing algorithms which allow for the en-
`nary signal. The control signal informs controller 114
`cryption and decryption of messages (signals) which are tiO that hybrid 122 has a decryption algorithm that matches
`transmitted or received respectively by radio 100. We
`the algorithm that was used to encrypt the incoming
`will assume for this discussion that the default hybrid
`signal, and the signal is then decoded in hybrid 122 in
`(the hybrid currently selected by the radio user) is by-
`order to produce a 12 Kbit/second digital voice signal
`(same as that produced by the CVSD AID converter of
`brid 124. The binary signal (cipher text in) in this case is
`sent from the interface and control circuit 116 to hybrid 65 the transmitting radio). The digital voice signal which is
`124 via bus 146. If hybrid 122 had been the default
`normally called decoded RX data or plain text out is
`hybrid the signal would have been sent via bus 144.
`then sent via bus 158 through decoder 120 and through
`Once hybrid 124 receives the binary signal an attempt is
`bus 170 to the CVSD converter 118 which performs a
`
`

`
`5,199,069
`
`5
`6
`encryption hybrid (i.e. hybrid 124) is using, by sending
`digital to analog conversion of the digital voice signal
`which, in turn, is routed via line 160 as a decrypted
`a message to controller 114 which can automatically
`select either a different key for the different hybrids, or
`analog signal to receiver 108. Receiver 108 finally pres-
`select different hybrids depending on the radio user's
`ents the resulting analog voice message via speaker 134
`to the user. If the selected hybrid would have been s command (e.g. changes to a new communication chan-
`nel which has a different encryption algorithm strapped
`hybrid 124 the digital voice signal would have been sent
`via bus 152 through decoder 120 and through bus 170 to
`to it).
`In Fig. 2, the software algorithm which is stored in
`the CVSD converter 118 for performance of the digital
`to analog conversion.
`radio controller 110 and executed by controller 110
`If the specific encryption key ·which is presently 10 once an encrypted message (signal) is received by radio
`100, is shown. When the signal is received it is routed
`being used does not match the key used in the encryp-
`tion process, the CVSD converter 118 will send a "no
`from receiver 108 to interface and control circuit 116,
`which in turn determines if the received signal is indeed
`proper code" message via bus 140 to controller 114,
`which, depending if the option to only unmute on
`a coded signal. If the signal is determined to be "clear"
`proper code has been set, will not unmute receiver 108. 15 (nonencrypted) the encryption circuit is not utilized,
`Unmute on proper code is normally selected since if the
`but if it is determined that the signal is encrypted, then
`controller 110 executes an encryption hybrid selection
`specific encryption key presently selected and the key
`used to encrypt the incoming signal do not match, only
`routine in accordance with the present invention. In
`step .202 the algorithm determines if "hybrid roaming"
`noise will be heard at speaker 126, since the digital
`signal will not have been properly decrypted. If the 20 (automatic encryption algorithm selection) is enabled.
`In other words is the present i.J;tvention of selecting from
`incoming digital signal is properly decrypted by con-
`among different encryption hybrids turned on, or is the
`verter 118 (encryption keys matched) then a proper
`code detected message is sent to controller 114 which in
`radio 100 going to look only at the presently selected
`hybrid 124 or 122. If automatic hybrid selection is· not
`turn notifies controller 110 that it is proper to unsquelch
`25 enabled, the program exits at step .204. If hybrid roam-
`the receiver 108.
`Although radio 100 is shown with only two encryp-
`ing is selected, the step .206 has controller 114 com-
`tion hybrids 124 and 122, one skilled in the art will
`mence to look for the in synch signal coming in on line
`150 or 148 depending on which hybrid 124 or 122 is
`realize that any number of encryption algorithms can be
`presently selected. Step .208 determines if the currently
`utilized. The only changes required in order to support
`greater numbers of encryption hybrids, is to add more 30 selected encryption hybrid (124 or 122) has properly
`decrypted the incoming encrypted signal. If the two
`capabilities to the decoding means which is used to
`algorithms match, an in synch signal (control signal) is
`select the individual encryption hybrids. Added hybrid
`capability can be accomplished by adding more input
`sent to controller 114 from hybrid 124 (assuming this is
`ports to controller 114 in order to receive the control
`the currently selected hybrid) and the routine in step
`signal messages from the different hybrids, and by add- 35 212 keeps the same encryption hybrid selected for the
`ing more address/data bus capabilities to decoder 120 in
`duration of the incoming signal even though this was
`not the user default hybrid. If the in synch signal is not
`order to allow for the transfer of information from the
`greater number of encryption hybrids with each one of
`found once the encrypted signal enters hybrid 124, step
`the hybrids having there own data buses.
`210 switches the selected hybrid to hybrid 122 as ex-
`The sequence utilized when radio 100 wants to trans- 40 plained previously, which is by sending a signal to de-
`mit an encrypted message will now be considered in
`coder 120 to change buses from bus 152 to bus 158 and
`order to understand how the transmission sequence
`enables the new hybrid. After the hybrids are switched,
`operates: It will be assumed that the radio is using en-
`the routine again looks for a synch signal (control sig-
`nal) in step .208 which informs the controller 114 that
`cryption hybrid 124 as the default encryption hybrid.
`Once transmitter 106 is "keyed up", a users voice mes- 45 the correct encryption algorithm has been selected. If
`sage is picked up by microphone 128 and translated into
`again no in synch signal is detected after trying all of the
`hybrids, the default hybrid is reselected but no message
`an electrical signal which transmitter 106 can utilize.
`The analog signal is then sent via bus 172 to the CVSD
`is sent to radio speaker 134 since successful decryption
`converter 118. The analog signal is then converted to a
`was not capable.
`12 kbit/sec digital voice signal by converter 118 by SO
`FIG. 3 shows a flow chart of the steps which occur
`after an incoming encrypted message has terminated. In
`performing an analog to digital conversion. The digital
`voice signal (plain text in) is then routed via bus 164 (bus
`step 302, the radio controller 110 first determines
`162 if hybrid 122 had been the selected hybrid) to en-
`whether or not the user default encryption hybrid is
`currently selected. The default hybrid is the hybrid
`cryption hybrid 124 in order to encrypt the digital voice
`signal assuming hybrid 124 was the default hybrid. ss currently selected by the radio user. If the default hy-
`Once the signal is encrypted (cipher text out), it is
`brid is currently selected, the controller exits the rou-
`tine in step 304 and does not change anything. If the
`routed via bus 152 through decoder 120 to the interface
`and control circuit 116 via bus 168, and finally through
`default hybrid is not currently selected (which occurs
`bus 138 to transmitter 106. Transmitter 106 then con-
`when a previous encrypted message was encrypted
`verts the encrypted signal into an R.F. signal for trans- 60 with 8n encryption algorithm found in another hybrid
`other than the default hybrid) the routine goes to step
`mission. If the selected hybrid had been hybrid 122 the
`. cipher text out would have gone through bus 158
`306, where the receive hangtime is retrieved from the
`controller's memory. Receive hangtime is the amount
`through the decoder 120 to the interface and control
`circuit 116 and finally through bus 138 to transmitter
`of time the radio 100 will keep the automatically chosen
`65 hybrid selected after the termination of an incoming
`106.
`message. This allows a radio user to receive subsequent
`Radio controller 110 can inform controller 114 at any
`time as to when the radio user wants to change either
`messages even though the messages are encrypted with
`an encryption algorithm that is not the encryption algo-
`encryption hybrids 124 and 122, or change the key the
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`5,199,069
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`hangtime which allows the radio 100 to transmit with
`rithm which the radio user had selected (i.e. the default
`hybrid). If the receive hangtime is equal to zero, step
`the new encryption algorithm within a predetermined
`time period (amount of time in transmit hangtime timer)
`308, the default hybrid is selected in step 310 and the
`routine is exited in step 312. In step 314, controller 114
`before reverting back to the defaulted hybrid. By hav-
`begins to decrement the receive hangtime timer which S ing more than one encryption algorithm residing in a
`is stored preferably in onboard memory which is part of
`radio, a radio user can communicate with other radio
`controller 114. In step 316, the radio receiver 108 is
`users which are using different encryption algorithms.
`One skilled in the art will realize that the present inven-
`looking for an incoming encrypted message, and con-
`troller 114 is waiting to determine if the incoming signal
`tion can be combined with the invention disclosed in
`is using the same encryption algorithm as the one that is 10 U.S. Pat. No. 4,440,976, which describes how to auto-
`presently selected. If the incoming signal is using ·the
`matically pick from a gro'!lp of keys belonging to one
`same encryption algorithm as the radio has currently
`specific encryption algorithm. By combining the two
`selected, then the receive hangtime timer is reset in step
`inventions into one radio 100, radio 100 could not only
`324, and the routine is sent back to step 308. If the in-
`automatically select from a plurality of encryption algo-
`coming signal is not using the same algorithm, in step lS rithms, but could also once the correct encryption algo-
`318 the receive hangtime timer is checked to see ifit has
`rithm is matched, to locate simultaneously the correct
`reached zero, if not, steps 314 and 316 are repeated. If
`encryption key that the incoming encrypted signal is
`the receive hangtime timer has reached zero without a
`using.
`new encrypted signal having been received by receiver
`Summarizing the steps involved in automatically
`108, the user default encryption hybrid is reselected 20 selecting a proper encryption algorithm from among a
`(124 or 122) and the routine is exited in step 322.
`plurality of different algorithms includes the steps of:
`In FIG. 4 a flowchart of what occurs when the radios
`attempting to decrypt the encrypted digital signal with
`push to talk is pressed and the radio is not in transmit
`one of the plurality of different algorithms; determining
`hangtime is shown. Transmit hangtime is the amount of
`if the algorithm chosen to decrypt the encrypted signal
`time after transmitting with an encryption hybrid other 2S has properly decrypted the encrypted signal; and devel-
`than the default hybrid that another transmission can
`oping a control signal upon the proper decryption of the
`occur without reverting back to the default hybrid. In
`encrypted signal in order to indicate correct encryp-
`step 402, it is determined if the radio 100 has the default
`tion. While the present invention has been described in
`hybrid currently selected. If the default hybrid is deter-
`conjunction with specific embodiments, it is evident
`mined to be currently selected, the PTT is processed 30 that many alternatives, modifications and variations will
`normally using the default hybrid in step 404, and the
`be apparent to those skilled in the art in light of the
`program is exited in step 406. If it is found that the
`foregoing description. For example, instead of u5ing a
`transmit hangtime delay timer does not equal zero, and
`radio controller 110 and an encryption circuit control-
`that radio is in the encrypted mode of operation (user
`ler 114, one larger controller could be used. Accord-
`wants to transmit encrypted messages) then the radio 3S ingly it is intended that the present invention embrace
`100 will transmit with the currently selected hybrid in
`all such alternatives, modifications, and variations as fall
`step 404 (in this case the selected hybrid is not the de-
`within the spirit and broad scope of the appended
`fault hybrid), and then routine is exited in step 406. If all
`claims.
`the conditions in step 408 are not found to be true, then
`What is claimed is:
`in step 410, the receive hangtime is set to zero and the 40
`1. A radio capable of automatically selecting a proper
`default hybrid is reselected. Finally, the transmission is
`algorithm from among a plurality of different algo-
`transmitted using the default hybrid in step 404 and the
`rithms, each having an associated key, for decrypting an
`routine exited in step 406.
`encrypted signal which is received by the radio and one
`FIG. 5 illustrates a flowchart of the steps involved
`of the plurality of algorithms in the radio is designated
`once the push to talk button is released by the radio user 4S to be a default algorithm, the radio comprising:
`after completing any encrypted transmission. In step
`a. means for automatically decrypting the received
`502, it is first determined if radio 100 was transmitting
`encrypted signal with one of the plurality of differ-
`with the user default encryption hybrid. If the last trans-
`ent algorithms;
`mission prior to releasing the PTT was with the default
`b. means for determining if the algorithm chosen to
`hybrid, the routine is automatically exited in step 516. If SO
`decrypt the encrypted signal has properly de-
`the last transmission was not with the default encryp-
`crypted the encrypted signal and selecting another
`tion hybrid, step 504 loads the transmit hangtime delay
`algorithm from among the plurality of algorithim.s
`timer and the timer is decremented in step 506. In step
`if the encrypted signal has not been properly de-
`508, the routine looks to see if the PTT has been pressed
`crypted: and
`again, if yes, the routine resets the timer in step 510, and SS
`c. means for developing a control signal upon the
`returns to step 506. If PTT has not been pressed again,
`proper decryption of the received encrypted signal
`step 512 determines if the transmit hangtime timer has
`in order to indicate correct decryption.
`decremented to zero, if yes, the routine selects the de-
`2. A radio as defined in claim 1, wherein the control
`fault hybrid and exits in step 514. H the timer has not
`signal is a signal which is produced by an encryption
`reached zero, the routine goes back to step 506.
`60 hybrid which stores the algorithm used to properly
`In summary, the present invention provides a radio
`decrypt the encrypted signal.
`100 which has more than one unique encryption algo-
`3. A radio as defined in claim 1, further comprising
`rithm (encryption hybrids 122 and 124) the ability to
`d. means for setting a transmit hangtime timer upon a
`automatically determine if the incoming signal matches
`control ·signal being developed and the default
`(achieves proper decryption) anyone of the hybrids 6S
`algorithm not being presently selected.
`(algorithms) in the radio 100. If any of the hybrids
`4. A radio as defined in claim 1, further comprising:
`match and it is not the currently selected hybrid, the
`d. means for setting a receive hangtime delay timer
`radio 100 selects the new hybrid and sets a transmit
`once a control signal is developed if the algorithm
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`which is being used to decrypt the encrypted signal
`is not the default encryption algorithm.
`5. A radio as defined in claim 1, further comprising:
`d. means responsive to the means for developing a 5
`control sign