EP0050268A1 - Apparatus for encrypted transmission of information - Google Patents

Abstract

The invention relates to a device for encoded information transmission in digitised form by radio between two and more transmitting/receiving stations, particularly mobile stations, in which the PN generator (PN-G) which generates the code signals and can be adjusted by a code has a relatively short period of PN sequences and the code of the code generator (SG) is continuously combined, at least partially, with the binary output signal of the station clock (G, TK, EV) to form a new code in a predetermined manner, for example by a modulo-2 addition, by means of a sequence control (AST) in time intervals which are less than the period of the PN sequences, with simultaneous resetting of the PN generator to a predetermined initial position, the PN generator being connected to the encoder (MD2) via a buffer store arrangement (ZA) bypassing the continuous new setting of PN sequences. <IMAGE>

Description

The invention relates to a device for encrypted information transmission in digitized form via radio between two or more transceiver stations, in particular mobile stations, for transmitting and for decoding the digital signals in a key transmitter by a key transmitter with regard to its PN adjustable sequence PN generator having and in which the mutual synchronization of the encryption units of the individual stations ge by quartz-controlled co-rotating station clocks _- is .währleistet.

Devices of this type are known for example from DE-PS 19 48 096, 20 48 199 and 21 56 635. Encryption devices, which are intended to ensure a high level of security against unauthorized eavesdropping on the information to be transmitted, are generally implemented with PN generators controlled by a day key, which have a very large PN sequence period. PN generators with very long PN sequence periods require lengthy, single-phase procedures between the interconnecting stations, which are also sensitive to interference. This situation has a particularly unfavorable effect when such key devices are used in tactical operations, where in addition to high-quality secret protection of the information against decryption, an encrypted selective call procedure with a short response time and secure and interference-free synchronization of the information encryption are required.

The invention has for its object to provide a high-quality encryption encryption device for a radio network, in particular a mobile radio network, which allows an encrypted selective call with short response time with secure and interference-proof synchronization.

Starting from a device for encrypted information transmission of the type mentioned in the introduction, this object is achieved according to the invention in that the PN generator has a relatively short PN sequence period and the key of the key transmitter in the PN sequence period falling below time intervals by means of a sequence control in fixed predetermined way, for example by a modulo-2 addition, is at least partially continuously linked to the binary output signal of the station clock to a new key, with simultaneous resetting of the PN generator to a predetermined starting position, and that the PN generator with the key is connected via a buffer arrangement which bridges the continuous PN sequence readjustment.

The invention is based on the essential finding that high-quality encryption can also be implemented using a PN generator which has only a relatively short PN sequence period if the day key defining this PN generator in its PN sequence is in good time before a PN Sequence period, i.e. in relatively short time intervals with simultaneous resetting of the PN generator, is changed, and that this change can be brought about in an extremely advantageous and simple manner by linking the digital output signal of the station clock with the day key without influencing the safe and interference-free synchronization .

The buffer arrangement provided for bridging the continuous PN sequence readjustment can easily have two PN sequence registers, which are alternately periodically switched on the input side via a first switch to the PN generator and alternately periodically on the output side via a second switch to the key switch . Both change-over switches actuated by the sequential control system have the same changeover period predetermined by the periodic resetting of the PN generator, but with a mutual temporal phase shift of preferably 180 °.

Since the synchronism of the radio network is guaranteed over long periods of time by the station clocks of the different stations that have been set and only if necessary the quartz drift between two stations that are in contact with one another needs to be fine-tuned by a time signal, an encrypted selective call with extraordinary can be made in this way realize a short reaction time.

In a further development of the invention, the selective call can also be designed selectively with regard to the encryption itself in that the binary output signal of the station clock is supplemented by a binary subscriber number which, in the idle state of a station, has its own call number or the radio circuit address assigned to it and when a call is to be given is the call number of the station to be called, and that the binary output signal thus supplemented is continuously linked to the key of the key transmitter in the rhythm of the time intervals falling below the PN sequence period to a new key, with the PN generator being reset at the same time.

In another development, this selectively encrypted information exchange can also be implemented with simultaneous use of a frequency hopping method in that the output of the buffer arrangement is connected to a frequency address register via a gate circuit controlled by the sequence control, to the output side via a conversion memory of the synthesizer provided for frequency generation is switched on, and that the gate circuit is openly controlled before the start of one of the time slots provided for call purposes or a transmission or reception information block for a number of bits predetermined by the length of a frequency address. In this way it is achieved that each of the two communicating or communicating stations practically independently of each other always throws the same connection-selective frequency address in the rhythm of the frequency hops provided.

• Fig. 1 das Blockschaltbild einer Verschlüsselungseinrichtung nach der Erfindung
• Fig. 2 ein die Wirkungsweise der Erzeugung der Schlüsselsignale am Ausgang des PN-Generators erläuterndes Schema.

Using an embodiment shown in the drawing. for example, the invention will be explained in more detail below. Mean in the drawing

• Fig. 1 shows the block diagram of an encryption device according to the invention
• Fig. 2 is a diagram explaining the operation of the generation of the key signals at the output of the PN generator.

The circuit of FIG. 1 has on the right side the quartz generator G, to which the divider chain TK is connected. The divider chain TK has outputs for required clock signals T and further outputs at which the binary output signal of the station clock formed by the quartz generator G, the divider chain TK and the setting device EV is present. The adjusting device EV is used for same setting of all stations of the radio network at the start of operation. For this purpose, the outputs of the setting device EV are connected to a corresponding number of associated inputs of the divider chain TK. The binary clock signal is continuously written into the register R2, which in turn also has a number of memory locations for writing a subscriber number or a radio address. A subscriber number or a radio address is written into register R2 using the number setting NE.

On the left side of the circuit according to FIG. 1, the key transmitter SG is shown, which contains the daily key setting. The key transmitter is connected via its binary outputs to the register R1, in which the day key is stored in the form of a pulse pattern. 1 also has a key register SR, which contains the current setting key for the PN generator connected to it. The output of the PN generator is in turn connected to the key MD2 in the form of a modulo-2 adder via the intermediate storage arrangement ZA, the second input of which supplies the digital signal Sig to be encrypted, and the encrypted signal Sig 'is taken from its output. The receiving side is constructed in the same way, with the difference that the encrypted signal Sig 'is supplied from the left and the decrypted signal Sig occurs at the output. To clarify this fact on the reception side, the corresponding designations are entered in brackets in Fig..1.

The modulo 2 adder MD1 is provided for linking the time in register R2 including a subscriber number or a radio circuit address with the day key in register R1. With everyone from the expiry AST triggered new adjustment of the PN generator, the result of the link from the binary sequences written in the registers R1 and R2 is transferred to the key register SR and a new one specified by the changed key in the key register SR when the PN generator is reset to its zero position PN cycle started. The sequence control AST is controlled by the divider chain TK and, when a key is reset, outputs corresponding control signals to the PN generator PN-G, the registers R1 and R2 and the key register SR. The sequencer AST also controls the buffer memory arrangement ZA, which in turn consists of two PN sequence registers PN-R1 and PN-R2 and two switches U1 and U2 actuated by the sequencer AST. The switch U1 alternately connects the inputs of the PN sequence registers PN-R1 and PN-R2 to the output of the PN generator. The change takes place together with the resetting of the PN generator to its zero position. In the same way, the changeover switch U2 mutually connects the outputs of the PN sequence registers PN-R1 and PN-R2 to the one input of the key MD2. The switchover phase of the switch U2 is shifted by 180 ° compared to the switchover phase of the switch U1. In this way it is achieved that the PN sequence register is alternately filled with a new PN sequence of the PN generator depending on a key reset and then out to the key MD2. will read.

For a better understanding of this mode of operation, three cycles in the form of merging circles are shown in FIG. 2. Each PN sequence begins at the time of zeroing indicated by NS. The circuit PN-X represents a first PN sequence emitted by the PN generator, which occurs shortly before the PN sequence periods expire switching time UP then changes into a new PN sequence, which is represented by the circle PN-X + 1. This new sequence begins with the zeroing of the PN generator. At the end of this sequence, at the changeover time UP, the new PN sequence represented by the circle PN-X + 2 is transferred again, etc.

Since the association of the day key in register R1 with the station time and a subscriber number in register R2 for the setting key for the PN generator in the key register SR is also determined by the set subscriber number, the key signal at the output of the buffer arrangement ZA is subscriber number selective and in this way enables everyone to be set up To assign a connection for an information exchange to its own key, which has a very high security against decryption due to the constant modification over the time.

As has already been pointed out, the key device according to FIG. 1 can also be expanded in addition to obtain connection-selective frequency addresses when using a frequency hopping method. This extension is also shown in Fig. 1. The SYN synthesizer is controlled here by a frequency address register FA-R via a conversion memory USP. The frequency address to be stored in the frequency address register FA-R before the start of a time slot intended for call purposes or a transmission or reception information block is carried out by means of a gate circuit TR controlled by the sequence control AST, to which the key signal at the output of the buffer memory arrangement ZA is fed on the input side. The sequence control AST controls the gate circuit TR open for a time interval at the beginning of a call time slot or before the start of a transmission or reception information block. that is sufficient to write the number of bits, for example eight bits, specified by a frequency address into the frequency address register FA-R. In other words, both stations set to the same subscriber number each roll the same frequency addresses from the subscriber number-selective key signal and thus enable information to be exchanged. which is connection-selective both in terms of encryption and in terms of the frequency hopping program.

Claims (5)

1. Device for encrypted information transmission in digitized form via radio between two or more transceiver stations, in particular mobile stations, which, for transmitting and decoding the digital signals on the receiving side, have a PN which can be set by a key transmitter with regard to its PN sequence. Have generator, and in which the mutual synchronization of the key devices of the individual stations is ensured by quartz-controlled synchronous station clocks,
characterized in that the PN generator (PN-G) has a relatively short PN sequence period and the key of the key transmitter (SG) in the PN sequence period falling below time intervals by means of a sequence control (AST) in a predetermined manner, for example by a modulo -2 addition, at least in part with the binary output signal of the station clock (G, TK, EV) is continuously linked to a new key, with simultaneous resetting of the PN generator to a predetermined starting position, and that the PN generator with the key (MD2) is connected via a buffer arrangement (ZA) bridging the continuous PN sequence readjustment. 2. Device according to claim 1,
characterized in that the intermediate storage arrangement (ZA) has two PN sequence registers (PN-P1, PN-R2) which alternately periodically on the input side via a first switch (U1) to the PN generator (PN-G) and alternately periodically on the output side a second changeover switch (U2) can be connected to the key (MD2), and that both changeover switches operated by the sequential control system (AST) do the same through the perio dische reset of the PN generator predetermined switching period, but with a mutual temporal phase shift of preferably 180 °. 3. Device according to claim 1 or 2,
characterized in that the binary output signal of the station clock (G, TK, EV) is supplemented by a binary subscriber number which, in the idle state of a station, is its own call number or the radio circuit address assigned to it and, in the case of a call to be made, the call number of the station to be called, and that the binary output signal thus supplemented is continuously linked to the key of the key transmitter (SG) in rhythm with the time intervals falling below the PN sequence period to form a new key with simultaneous resetting of the PN generator (PN-G). 4. Device according to one of the preceding claims for stations operating with frequency hopping, characterized in that the output of the buffer arrangement (ZA) is connected to a frequency address register (FA-R) via a gate circuit (TR) controlled by the sequence control (AST), the synthesizer (SYN) intended for frequency generation is connected to the output side via a conversion memory (USP) and that the gate circuit is openly controlled before the start of a time slot specified for call purposes or a transmission or reception information block for a number of bits specified by a frequency address. 5. Device according to one of the preceding claims, characterized in that the mutual coarse synchronization of the station clocks guaranteed by the synchronism of the station clocks is supplemented by a time signal preceded by each broadcast in the sense of a fine correction of the quartz drift.

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