GB2084381A - A method of programming equipment for the secure transmission of messages - Google Patents

Abstract

A method and apparatus for programming equipment for the secured transmission of messages for example by encyphering or decyphering these messages, in which a program is passed to a transportable unit from a program generating unit, and from the transportable unit to the transmission equipment, by way of respective optical paths. <IMAGE>

Description

SPECIFICATION A method of programing equipment for secure transmission of messages and apparatus therefor This invention relates to a method of programing equipment for secure transmission of messages, for example by encyphering or decyphering these messages, and is also concerned with apparatus for use in carrying out such a method.

In a known kind of encyphering equipment, a message to be encyphered is in the form of a stream of binary digits (hereinafter termed 'bits') and is combined, for example by means of an exclusive -- OR gate, with a quasirandom sequence of bits. The equipment includes a generator which supplies an electric signal carrying the quasi-random sequence of bits, and there is provision for a large number of different sequences to be selected. Such a selection of sequences, known as code setting, is largely under the control of the user, for example by operation of multi-way electric switches by means of thumbwheels. The code setting may consist of a plurality of hexadecimal digits and clearly has a high security rating.It is convenient for the code setting which is to be used at any time to be looked up in an appropriate table and to be entered into a transportable unit at a location remote from the encyphering equipment, the transportable unit subsequently being taken to the location of the encyphering equipment and the code setting then transferred from the unit to the equipment for the purpose of programing the equipment for later encyphering. The decyphering equipment at another location is programmed in the same way.

With a transportable unit as just described, it has hitherto been necessary to make electrical connections to it by means of plugs and sockets both when a code setting is being written into the unit and when the code setting is being transferred from the unit to the encyphering/decyphering equipment. The necessary repeated engagement and disengagement of the plugs and sockets results in heavy wear of those items and one object of the present invention is to provide a method of programing equipment for secure transmission of messages, such as encyphering or decyphering equipment, involving a transportable unit to carry a selected program to the equipment without the need to make electrical connections to the unit.

Another object of the invention is to provide a novel construction of transportable unit for carrying a code setting to encyphering/decyphering equipment for subsequent transfer thereto.

Yet other objects of the invention are to provide novel constructions of apparatus for entering a code setting into a transportable unit and of encyphering and decyphering equipment.

In a method of programing equipment for secure transmission of messages according to one aspect of the present invention, the program is first entered into data storage means of input apparatus by operation of manually-operable means of the input apparatus, the program entered in said storage means is transferred via an optical path to data storage means of a transportable unit, the transportable unit is conveyed to the location of a transmitter or a receiver forming part of said equipment and the program stored in the storage means of the transportable unit is transferred via an optical path to said transmitter or receiver.

In a method of programing equipment for encyphering or decyphering messages according to another aspect of the present invention, the program is first entered into data storage means of input apparatus at a different location to that of the encyphering or decyphering equipment by operation of manually-operable means of the input apparatus, the program entered in said storage means is transferred via an optical path to data storage means of a transportable unit, the transportable unit is conveyed to the location of the encyphering or decyphering equipment and the program stored in the storage means of the transportable unit is transferred via an optical path to the encyphering or decyphering equipment.

According to another aspect of the invention, a transportable unit for use in carrying out the method specified in either of the last two paragraphs may, in addition to the data storage means previously mentioned, comprise an input port having light-sensitive means, means for writing into said storage means data corresponding to the sequence of light pulses received by the light-sensitive means, an output port having light-emitting means, manuallyoperable means and means responsive to operation of the manually-operable means to cause the light-emitting means to transmit a sequence of light pulses carrying the data stored by the storage means.

More particularly, a transportable unit for use in carrying out the method previously specified preferably comprises an input port having lightsensitive means, a data store, means for writing into the storage data corresponding to a sequence of light pulses received by the light-sensitive means, error checking means for checking that a complete data group has been correctly received, an output port having light-emitting means, manually-operable means and means responsive to operation of the manually-operable means to supply signals to the light-emitting means to cause that means to transmit a sequence of light pulses carrying the data stored by the store.

Preferably the transportable unit is selfpowered so that no electrical connection thereto is necessary either when entering a program into the unit or when transferring the program from the unit to message transmission equipment such as encyphering or decyphering equipment. The unit may have provision for data stored thereby to be erased by a manual operation.

According to another aspect of the invention.

input apparatus for use in carrying out the method specified above may, in addition to the manuallyoperable means previously mentioned, comprise data storage means arranged to store data dependent upon operation of the manuallyoperable means, an output port having lightemitting means, means responsive to operation of further manually-operable means to cause the light-emitting means to transmit a sequence of light pulses carrying the data stored by the data storage means.

Preferably the input apparatus also includes an input port having light-sensitive means, further data storage means, means for writing into the further storage means data carried by a sequence of light pulses received by the light-sensitive means and means to give an indication as to whether or not the data stored by the further storage means is the same as that stored by the previously mentioned storage means. With this arrangement, the accuracy of a program loaded into a transportable unit via the output port of the input unit may be checked by feeding the program stored by that unit to the input apparatus via the input port thereof.

Equipment for encyphering or decyphering messages according to yet another aspect of the invention includes, for the purpose of enabling the equipment to be programed, an input port having light-sensitive means, a buffer data store, means for writing into the buffer store data corresponding to a sequence of light pulses received by the lightsensitive means, error-checking means responsive to the data stored by the buffer, a main data store and means for writing data from the buffer store into the main data store upon the error-checking means signifying that a complete data group has been correctly received.

For the purpose of signallying binary data to or from said transportable unit, the sequence of light pulses to which reference has previously been made are width modulated so that each such pulse carries the value of one binary digit. With this form of signalling, any one of the said input apparatus, said transportable unit and said encyphering or decyphering equipment preferably includes circuitry which is responsive to the signal supplied by said light-sensitive means associated with the input port thereof, said circuitry comprising a monostable circuit which is arranged to be triggered to its unstable state by the leading edge of each pulse of that signal and which resets to its stable state after a time less than the recurrence period of such pulses and a sampieand-hold circuit which samples the signal supplied by the light-sensitive means upon resetting of the monostable circuit to derive a signal carrying the data.

One example of a system for the secure transmission of speech messages or other signals will now be described with reference to the accompanying drawings, of which Figures 1 and 2 show different parts of the system diagrammatically, and Figures 3 and 4 respectively show in block schematic form the electric circuits of the parts of the system shown in Figures 1 and 2.

Referring to the drawings, the security of transmission is achieved by supplying encyphering and decyphering equipment at each terminal of the system with a program which characterises the encyphering process so as to enable the two terminals to work together in the desired manner.

The complete program consists of a large number of binary digits. Some of these digits, which may constitute a minor part of the program, are fed into the equipment by manual operation of a set of sixteen-position electric switches by means of thumb-wheels and the remainder are generated at a remote location by means of the key management unit 1 shown in Figures 1 and 3, in a manner to be described, and are conveyed to the encyphering or decyphering equipment by means, of a transportable unit 2 shown in Figures 2 and 4.

At the remote location, the transportable unit 2 is loaded from the unit 1, which is arranged temporarily to store the appropriate part of the complete program and which is manuallyoperable to enable the program to be set up. For that purpose, the input unit 1 comprises a hexadecimal keyboard 3 having sixteen appropriately labelled keys, a function keyboard 4 and an alpha numeric display 5 which provides for a plurality of hexadecimal digits to be presented in a horizontal line.

To enter a program, a plurality of operations of the keys of the hexadecimal keyboard 3 are effected, typically the plurality is in excess of twenty. The relevant hexadecimal numbers, as determined by the keys operated, are stored in a data store 6 in binary form, each hexadecimal number being represented by four binary digits which form part of the eventual program to be used by the encyphering or decyphering equipment (not shown). As each dexadecimal digit is entered, it is displayed on the display 5 against an index mark (not shown) and previously entered digits are moved sideways.This enables the entered digits to be checked and by operation of one or other of two shift keys of the function keyboard 4, which keys permit the stored digits to be shifted in the display to the left and to the right" respectively, any digit can be brought to the index mark position and then can be corrected, if in error, by operation of the appropriate hexadecimal key to overwrite the correct aigit.

Some or all of the key numbers may be generated by a random number generator 7 under the control of selector circuit 8 controlled from a microprocessor central controller 9.

The unit 1 may also have provision for automatically writing into the store 6 some additional binary digits which form a small part of the eventual encyphering/decyphering program.

The values of these digits may be unique to a particular customer and may be preset during manufacture of the apparatus.

The unit 1 has a conical recess (not shown) in its housing, this recess containing a light-emitting, diode 10 and providing a light output port for the unit 1. The transportable unit 2 has a conical projection 11 containing a photo diode 12 and providing a light input port for the unit 2.When the transportable unit 2 is to be loaded with program information from the unit 1, one end of the unit 2 is placed within a well 13 in the surface of the unit 1, so that the projection 11 fits into the conical recess (not shown) which lies at the base of the well 13, the photo diode 12 and the lightemitting diode 10 then lying opposite one another When program information has been entered into said data store 6 and the transportable unit 1 is in the loading position as just described, that information may be signalled as a sequence of light pulses over the light path between the output port of the unit 1 and the input port of the transportable unit 2 by pressing a 'Write' key of the function keyboard 4 of the unit 1.

In the sequence of light pulses, which are regularly recurrent, each pulse represents one bit and is either of relatively short duration to signify the bit value '0' or of relatively short duration to signify the bit value '1'. For example, if the pulse recurrence frequency is 1.5 kiloherz, each pulse may have a duration of either 50 or 350 microseconds. The full sequence is made up of two consecutive parts each containing the same number of pulses, the first part representing the data stored by said data store 6, and the second part representing the binary complement or inverse of the data stored by said data store 6.

The consequence of signalling a aforesaid from the unit 1 to the transportable unit 2 is that the photo diode 12 of the unit 2 supplies a signal consisting of a sequence of width-modulated pulses. This signal is fed to a pulse-width measuring circuit 14 comprising a sample-andhold circuit (not shown) and a monostable circuit (not shown) which is triggered to its unstable state by the rising edge of each pulse. The monostable circuit is arranged to reset to its stable state after a time less than the duration of the longer pulses, which is of course less than the recurrence period, and the sample-and-hold circuit is arranged to sample the signal when the monostable circuit resets. The sample-and-hold circuit thus supplies a binary signal representing the received data in serial form.This binary signal is passed by way of a load/write switch 1 5 and a gate circuit 1 6 to a store 1 7 into which the received data is written under the control of signals derived from a timing generator 1 8.

The transportable unit 1 has an error-checking circuit 1 9 responsive to the received pulse signal and to the data stored by the store 17. In this connection, it will be appreciated that before the transportable unit 1 is loaded with data, the photo diode 1 2 of that unit may respond to any light falling on it, and this may result in one or more spurious bits being written into the store although such bits have no significance as far as encyphering is concerned and must be cancelled.

Thus if any spurious light pulses are received the effective clock rate of these pulses will in general be rejected as too slow by a clock rate detector 20, and accordingly a reset circuit 21 will reset a loading counter 22.

When a series of light pulses representing a program are received from the unit 1, however, the first part of the series, of up to 128 binary signals, is entered in the store 17 under the control of the clock source 1 8, which also steps the counter 22 through a first count of 128. As the second part of the series of light pulses is received the corresponding binary signals are inverted by the gate 1 6 and are entered in the store 1 7. At the same time the first set of binary signals are read from the store 17 and the two sets of signals are compared by the error detector 19. If an error is detected the counter 22 is reset ready for a fresh loading sequence.

If no error is detected by the end of the second set of pulses, that is, after a count of 256, a count decoder circuit 23 applies a signal to a load/write control circuit 24, which in turn enables an output driver circuit 25 and switches the load/write switch 1 5 to 'write'. During a third set of 128 pulses from the clock generator 1 8 the second set of binary values, now stored in the store 17, is read out in series to a pulse width modulator circuit 26 and thence to a light-emitting diode 27 by way of the driver circuit 25, and at the same time this second set of values is retu med -to the the store 1 7 by way of the switch 1 5 and the gate 1 6. The unit 2 therefore provides confirmation of correct loading by a light pulse sequence from the diode 27.

As shown in Figure 2 the housing of the transportable unit 2 is in the shape of a flat rectangular box. The conical projection 11 providing the light input port of the unit is located on one end of the housing together with a light output port 28, this output port 28 being similar to that of the unit 1 (not shown) and comprising a conical recess having the light-emitting diode 27 at its inner end. When the transportable unit 1 is loaded with data and either one of two pushbuttons 29 located on opposite sides of the housing is pressed, the load/write control circuit 24 of the unit 2 causes the data to be read from the store 1 7 and the generation of widthmodulated pulse signals which are supplied to the light-emitting diode 27 so as to cause a sequence of light pulses carrying the stored data to be transmitted from the output port 28.

The transportable unit 2 has an internal longlife battery (not shown) so that it is self-powered.

The circuitry of this unit 2 is all of CMOS inegrated circuit form so that the power required to be supplied by the battery is low. Furthermore the unit 2 may include a bistable circuit (not shown) which is triggered upon the store 1 7 being loaded with data to de-energise the circuit 14 to economise on power consumption.

The system has provision to enable the correct loading of data from the unit 1 to the transportable unit 2 to be checked. For this purpose the unit 1 has a light input port (not shown) which is similar to the port 11 of the transportable unit 2 and which is located alongside the light output port (not shown). Associated with this light input port, the unit 1 has circuitry responsive to the signal supplied by the photo diode 30 (Figure 3) of the input port similar to that of the transportable unit 2. When the transportable unit 2 is being loaded, its positioning within the well 13 of the unit 1 ensures also that the light input port (not shown) of the unit 1 fits into the recess of the light output port 28 of the transportable unit 2.During the third set of 128 pulses referred to above the sequence of light pulses from the diode 27 are received by the diode 30. a comparison key of the function keyboard 4 of the unit 1 is then pressed and this causes each received bit to be compared with the corresponding bit held in the store 6. The result of this comparison is presented visually as 'PASS' or 'FAIL' on the display 5. If this comparison discloses a lack of correspondence, the identity of the digit in error may be ascertained by pressing another key of the function keyboard 4 which causes the location of the fals digit (or digits) to be shown on the display 5.

After being loaded with data and checked, the transportable unit 2 may be conveyed to the location of the encyphering or decyphering equipment (not shown) which is to be programmed. The method of signailing the stored data to that equipment is essentially the same as that previously described for signailing data optically from the unit 1 to the transportable unit 2. More particulariy that equipment has a projecting light input port which is arranged to fit into the light output port 28 of the transportable unit 2 and circuitry corresponding to that of the transportable unit 2 up to and including the store 1 7 thereof. There is provision for checking that only required data is received and that the program information is correct (at least to the extent that any single eror would be detected).

To supply data from the transportable unit 2 to encyphering or decyphering equipment, all that is involved is to mate the light output port 28 of the unit 2 with the light input port of the equipment and to press one or other of the push-buttons 29 of the unit 2. This operation is non-destructive as far as data stored by the transportable unit 2 is concerned. The unit 2 does however have provision for the data stored thereby to be cancelled by simultaneously pressing both buttons 29, which are on opposite sides of the unit 2 to minimise the likelihood of both buttons accidentally being pressed simultaneously.

The construction of transportable unit 2 described above enables such a unit to be loaded with data from a similar unit instead of from the unit 1. For this purpose it is merely necessary for the light output port 28 of a first unit 2 which is loaded with data to be mated with the light input port 11 of the second unit 2 which is to be loaded and for one of the push-buttons 29 of the first unit 2 to be pressed.

In some circumstances it may be undesirable for program data to be written from one transportable unit 2 to another as described in the last paragraph and there may be provision for this facility to be controlled when the program is initially supplied to the unit 1. For this purpose the function keyboard 4 has two keys (in place of the single 'Write' key previously mentioned) one of which is used when the facility is to be available and the other used when it is not. In both cases the stored program is signalled as before but different control data is signalled for the two cases. A transportable unit 2 to which a program may be written from another transportable unit 2 is arranged only to store such a program if the appropriate control bits are present.

Control bits may also be used for addressing a particular store within the encyphering or decyphering equipment. When so used, code settings may be automatically stored for future use without intervention by an operator.

It may also be convenient to know the number of times program data is read out from a transportable unit 2. For that purpose, the transportable unit 2 may have an internal counter (not shown) which counts the number of operations of the push-buttons 29, a group of the control bits stored by the transportable unit 2 characterising the result of this count. When the unit 2 returns to the location of the unit 1, it is mated with that unit 1 (as when checking the initial loading) and a further key of the function keyboard 4 is pressed, causing the display 5 of the unit 1 to present the number characterised by this group of control bits.

In the manner of signalling used in the embodiment described above, the sequences of light pulses are width modulated by the data to be transmitted but it is to be understood that other forms of serial data transmission may be employed within the scope of the invention. For example, the pulse signal supplied to the lightemitting diodes 10 and 27 may have a non-returnto-zero waveform although, in that case, it would have to be preceded by a few pulses to enable a clock pulse generator to be correctly synchronised before the data-carrying pulses are received.

It will be appreciated that the transportable unit 2 may be used to carry a program denoting a sequence of frequencies in a "frequency-hopping" transmission system.

Claims (14)

1. A method of programing equipment for secure transmission of messages, wherein the program is first entered into data storage means of input apparatus by operation of manually-operable means of the input apparatus, the program entered in said storage means is transferred via an optical path to data storage means of a transportable unit, the transportable unit is conveyed to the location of a transmitter or a receiver forming part of said equipment and the program stored in the storage means of the transportable unit is transferred via an optical path to said transmitter or receiver.

2. A method of programing equipment for encyphering or decyphering messages, wherein the program is first entered into data storage means of input apparatus at a different location to that of the encyphering or decyphering equipment by operation of manually-operable means of the input apparatus, the program entered in said storage means is transferred via an optical path to data storage means of a transportable unit, the transportable unit is conveyed to the location of the encyphering or decyphering equipment and the program stored in the storage means of the transportable unit is transferred via an optical path to the encyphering or decyphering equipment.

3. A transportable unit for use in carrying out the method specified in Claim 1 or Claim 2 comprises, in addition to the data storage means previously mentioned, an input port having lightsensitive means, means for writing into said storage means data corresponding to a sequence of light pulses received by the light-sensitive means, an output port having light-emitting means, manually-operable means, and means responsive to operation of the manually-operable means to cause the light-emitting means to transmit a sequence of light pulses carrying the data stored by the storage means.

4. A transportable unit for use in carrying out the method specified in Claim 1 or Claim 2 comprises an input port having light-sensitive means, a data store, means for writing into the store data corresponding to a sequence of light pulses received by the light-sensitive means, error-checking means for checking that a complete data group has been correctly received, an output port having light-emitting means, manually-operable means and means responsive to the operation of the manually-operable means to supply signals to the light-emitting means to cause that means to transmit a sequence of light pulses carrying the data stored by the store.

5. A transportable unit in accordance with Claim 3 or Claim 4 which is self-powered so that no electrical connection thereto is necessary either when entering a program into the unit or when transferring the program from the unit to message transmission equipment such as encyphering or decyphering equipment.

6. A transportable unit in accordance with Claim 3, Claim 4 or Claim 5 wherein there is provision for data stored thereby to be erased by a manual operation.

7. Input apparatus for use in carrying out the method specified in Claim 1 or Claim 2 comprises, in addition to the manually-operable means previously mentioned, data storage means arranged to store data dependent upon operation of the manually-operable means, an output port having light-emitting means, and means responsive to operation of further manuallyoperable means to cause the iight-emitting means to transmit a sequence of light pulses carrying the data stored by the data storage means.

8..lnput apparatus in accordance with Claim 7 including an input port having light-sensitive means, further data storage means, means for writing into the further storage means data carried by a sequence of light pulses received by the lightsensitive means and means to give an indication as to whether or not the data stored by the further storage means is the same as that stored by the previously mentioned storage means.

9. Equipment for encyphering or decyphering messages including, for the purpose of enabling the equipment to be programed, an input port having light-sensitive means, a buffer data store, means for writing into the buffer store data corresponding to a sequence of light pulses received by the light-sensitive means, errorchecking means responsive to the data stored by the buffer, a main data store and means for writing data from the buffer store into the main data store upon the error-checking means signifying that a complete data group has been correctly received.

10. A transportable unit in accordance with Claim 3, Claim 4, Claim 5 or Claim 6 including circuitry which is responsive to the signal supplied by said light-sensitive means associated with the input port thereof, said circuitry comprising a monostable circuit which is arranged to be triggered to its unstable state by the leading edge of each pulse of that signal and which resets to its stable state after a time less than the recurrence period of such pulses and a sample-and-hold circuit which samples the signal supplied by the light-sensitive means upon resetting of the monostable circuit to derive a signal carrying the data.

11. Input apparatus in accordance with Claim 8 including circuitry which is responsive to the signal supplied by said light-sensitive means associated with the input port thereof, said circuitry comprising a monostable circuit which is arranged to be triggered to its unstable state by the leading edge of each pulse of that signal and which resets to its stable state after a time less than the recurrence period of such pulses and a sample-and-hold circuit which samples the signal supplied by the light-sensitive means upon resetting of the monostable circuit to derive a signal carrying the data.

12. Equipment in accordance with Claim 9 including circuitry which is responsive to the signal supplied by said light-sensitive means associated with the input port thereof, said circuitry comprising a monostable circuit which is arranged to be triggered to its unstable state by the leading edge of each pulse of that signal and which resets to its stable state after a time less than the recurrence period of such pulses and a sample-and-hold circuit which samples thesignal supplied by the light-sensitive means upon resetting of the mono-stable circuit to derive a signal carrying the data.

13. A method of programing equipment for secure transmission of messages substantially as hereinbefore described with reference to the accompanying drawings.

14. Input apparatus substantially as hereinbefore described with reference to Figures 1 and 3 of the accompanying drawings.

1 5. A transportable unit substantially as hereinbefore described with reference to Figures 2 and 4 of the accompanying drawings.