GB2289358A

GB2289358A - Electronic safety device and method

Info

Publication number: GB2289358A
Application number: GB9509589A
Authority: GB
Inventors: Thomas Roehrl
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1994-05-11
Filing date: 1995-05-11
Publication date: 1995-11-15
Anticipated expiration: 2015-05-11
Also published as: FR2719962B1; GB2289358B; FR2719962A1; DE4416705C1; GB9509589D0

Description

2289358 -I- ELECTRONIC SAFETY DEVICE AND METHOD FOR ITS OPERATION The

invention relates to an electronic safety device, in particular a departure blocking device for a motor vehicle. It also relates to a method for 5 operating such a safety device.

A known safety device (DE 39 27 024) has a stationary transceiver in the motor vehicle and an associated portable transponder.

The transceiver transmits a scanning signal which contains a random code word (random number) and an identification code word (called identifier in the following). Thereupon, the transponder only generates and returns a response signal if the scanning signal contains a legitimate identifier. The identifier is coded with the random number with the aid of several different mathematical operations. In this way the decoding of the code is made substantially more difficult even with repeated monitoring of the dialogue.

However, with such a safety device a bidirectional dialogue takes place between the stationary transceiver and the portable transponder. Therefore, both the transceiver and the transponder must first of all be coordinated or initialized before the dialogue can take place.

The present invention seeks to create an electronic safety device of the type named in the introduction, which with little expenditure offers a high level of protection from theft and which does not need to be initialized.

According to one aspect of the present invention, there is provided an electronic safety device for a motor vehicle, comprising a transmitter for generating and transmitting an alternating code word, a coding device arranged in the transmitter, which device generates an alternating code word, by using mathematical operations on at least two different base code words, a receiver which receives the alternating code word, a decoding device arranged in the receiver, which device decodes the received alternating code word with the aid of inverse mathematical operations and divides it into base code words, a coding device arranged in the receiver, which device, with the aid of the decoded base code words and with the same mathematical operations as in the transmitter, generates an alternating code word, is a comparison device which compares the received alternating code word and the alternating code word generated in the receiver with each other and generates a control signal if they correspond. According to a further aspect of the present invention, there is provided a method for operating such an electronic safety device comprising the following steps: generation and transmission of an alternating code word in the transmitter, through coding of the base code words, in that mathematical operations are used on them, decoding of the received alternating code word in the receiver, in that inverse mathematical operations are used on the alternating code word, and thus generation of base code words from the received alternating code word, generation of an alternating code word in the receiver, in that the same mathematical operations as in the transmitter are used on the decoded base code words, and comparison of the received alternating code word k and of the alternating code word generated in the receiver and generation of a control signal if they correspond. Thus, in a device in accordance with the invention, only a unidirectional transmission from a transmitter to a receiver takes place. The transmitter signal is coded with the aid of a mathematical algorithm and is transmitted to the receiver. The receiver decodes the received signal with the aid of the inverse mathematical algorithm and separates it into its earlier components. A code signal is generated in the receiver using the same algorithm as that used in the transmitter, and the resulting code signal is compared with the received signal. If the two signals are found to correspond the transmitter is accepted as legitimate. Since the algorithm is only known to the user and because the random number changes constantly, a high level of protection from monitoring is given. 20 For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a block diagram of an electronic safety device in accordance with the invention.

Figure 2 shows a flow chart to illustrate the method for operating the safety device according to Figure 1.

In Figure 1 a block diagram of an electronic safety device is shown, which can be installed, for example, into a motor vehicle. It serves the purpose of enabling the motor vehicle to be started only legitimately. However, the safety device is also suitable for other applications, for example for data exchange between two control devices in the motor vehicle to be protected from monitoring.

The safety device has a transmitter 1 and a receiver 2 which are connected to each other by way of a bus 3. In the transmitter 1 a random number generator 11 is arranged, which, upon actuation of a switch 12 or an electrical contact, generates a random code word (called random number in the following). Base code words are contained on the producer side in a memory unit 13, for example a ROM, of the transmitter 1. They can contain a user-specific identifier or certain control commands which are to be transmitted to the receiver 2. A coder 14 codes the random number together with at least one of the base code words, for example the identifier, and generates an alternating code word (called code signal in the following). The code signal is transmitted by a transmission unit 15 by way of a bus 3 to the receiver 2. The transmission between the transmission unit 15 and the bus 3 can take place electrically or also wirelessly. The receiver 2 has a receiving unit 21 which receives the code signal. A decoder 22 decodes the code signal and divides it into its component parts, i.e. into a bit sequence corresponding to the random number and a bit sequence corresponding to the identifier. The component parts of the code signal are supplied to a coder 23 and coded there, whereby a code signal is generated. The coded code signal is relayed to a comparison unit 24 which compares the received code signal with the coded code signal. 30 If the two code signals correspond, the transmitter 1 has transmitted the correct identifier, i.e. the transmitter 1 is accepted as legitimate. A control unit 25 thereupon generates a control signal which is relayed to an electronic unit in the motor vehicle and is carried into effect there. The invention is explained in more detail with Z 4 reference to the flow chart of Figure 2. With each actuation of the transmitter 1 the random number is generated. The random number consists of a bit sequence which was randomly generated according to a 5 specified pattern.

Several base code words are stored as bit sequences in the memory unit 13 (ROM). The base code words can contain the identifier of the transmitter 1 and/or also one or more control commands which are to be relayed by the receiver 2 to a control device and are to be carried into effect there. The identifier is conducted together with the random number to the coder 14 which uses one or more mathematical operations on these two bit sequences. The mathematical operations can be logic circuits, for example an EXOR-circuit. An algorithm programmed on the producer side can also be used on these two bit sequences.

The code signal which is transmitted to the receiver 2 is generated in this way. The procedural steps on the transmitter side are shown on the left side of Figure 2 and the procedural steps on the receiver side are shown on the right side of Figure 2.

The transmission between the transmitter 1 and the receiver 2 is symbolized by the lightning-shaped arrow.

The receiver 2 decodes the code signal, i.e. it calculates the code signal back with the aid of a mathematical operation which runs inversely to the mathematical operation in the transmitter 1. it therefore divides the code signal into two bit sequences which correspond to the identifier and the random number. The coder 23 codes these two bit sequences with the same mathematical operation as occurred in the transmitter 1 and generates a new code signal.

The newly generated code signal and the received code signal are compared with each other in the comparison unit 24. If the two code signals correspond, the transmitter 1 is accepted as legitimate and the code signal is then processed. A check calculation therefore takes place in the receiver 2, by means of which it is to be examined whether the transmitter 1 sent a signal to the receiver 2 legitimately. If it was legitimate, the control signal is then generated.

The control signal can contain a control command to a control device, not shown, in the motor vehicle. In this way the control signal can be a release signal for the departure blocking device, in that the release is communicated to the motor control or to another device controlling the ignition or the injection. The control signal can additionally contain the identifier of the transmitter 1.

The coding and decoding will be explained in more detail with reference to a concrete example, where the transmitter 1 may transmit the control command is generated.

be 11 5 11 hex = 117E11 hex (hexadecimal) = 1,0111 111011 bin (binary) to the receiver 2 and thus to a control unit connected to the bus 4. With actuation of the switch a random number 11B4All hex = 111011 0100 101011 bin The number of the transmitter 1 should 11010111 bin.

The number and the control command should be 35 transmitted together as identifier:

g; 1157E11 hex = 110101 0111 111011 bin.

The identifier is coded together with the random number with an EXORcircuit. The alternating code word 1M411 hex = "1110 0011 010011 bin is then obtained.

In addition, the random number must be added to the alternating code word so that the following alternating code word is available for transmission:

11B4A E3411 hex = 111011 0100 1010 1110 0011 010011 bin.

is Before the alternating code word is transmitted, a further coding takes place. This further coding may be, for example a bit displacement within the alternating code word (e.g. the last two 110011 of the binary word are displaced to the first points to the left), so that the following alternating code word is transmitted as code signal:

112D 2B 8W hex "0010 1101 0010 1011 1000 110111 bin.

The receiver 2 first of all cancels this bit displacement, separates the random number and likewise uses an EXOR-circuit on the transmitted code. The receiver 2 selects two bit sequences which correspond to the random number and the identifier. These are now coded exactly as in the transmitter 1 and from this an alternating code word is generated. This alternating code word coded in the receiver 2 is compared with the alternating code word received from the transmitter 1.

By means of this coding method with the random numbers, each transmitted piece of information is different to the previously transmitted piece of information. once a code signal has been transmitted it is no longer valid in the future. The transmission can therefore indeed be monitored, but the monitored signals cannot be used again. Since the mathematical algorithm, with which the code signals are coded and decoded, in the transmitter 1 and in the receiver 2 on the producer side are either set in terms of hardware or are programmed in terms of software, the user does not have to carry out any initialization of the system.

The safety device can be used as a departure blocking device. For this purpose the transmitter 1 is integrated into an ignition key, not shown. As soon as the ignition key is turned in the ignition lock, an electrical contact is closed, as a consequence of which the random number is generated. After that, the process in accordance with the invention takes place. With the aid of the identifier, it is communicated to the receiver 2 that the user is entitled to start the vehicle and that this should now happen. 20 The transmitter 1 can also be arranged in a control device of the motor vehicle, which is connected by way of the internal vehicle bus to a receiver 2 in a further control device. The process in accordance with the invention is used if security-relevant information is to be transmitted from the first control device to the second control device. An alternating code word is contained in the code signal. The used term "alternating code" presents a rule according to which code words are generated from a finite number of code words according to a certain algorithm. With each transmission the code words differ from those previously transmitted. It is therefore a mathematical sequence which is repeated after a finite number of transmissions - conditional upon the generation of the random number.

ir J1 c 1 is

Claims

1. Electronic safety device for a motor vehicl comprising a transmitter for generating and transmitting an alternating code word, a coding device arranged in the transmitter, which device generates an alternating code word, by using mathematical operations on at least two different base code words, a receiver which receives the alternating code word, a decoding device arranged in the receiver, which device decodes the received alternating code word with the aid of inverse mathematical operations and divides it into base code words, a coding device arranged in the receiver, which device, with the aid of the decoded base code words and with the same mathematical operations as in the transmitter, generates an alternating code word, a comparison device which compares the received alternating code word and the alternating code ward generated in the receiver with each other and generates a control signal if they correspond.

2. Safety device as claimed in claim 1, wherein one of the base code words is a random code word which is generated anew upon each actuation of the transmitter by a random generator arranged in the transmitter and in that another of the base code words is an identifier code word which is stored in a memory unit of the transmitter and which contains userspecific information or control commands.

3. Safety device as claimed in claim 1 or 2, wherein the transmitter and the receiver are connected to each other by way of a bus in the motor vehicle.

4. Safety device as claimed in claim 1 or 2, e, wherein the transmitter and the receiver are in each case arranged in a control device of the motor vehicle, whereby the control devices are connected to each other by way of the bus.

5 5. Departure blocking device for a motor vehicle with a safety device according to one of claims 1-4, whereby the transmitter is arranged on an ignition key and the receiver is arranged in a motor control device.

6. Method for operating an electronic safety device according to one of the preceding claims, comprising the following steps: generation and transmission of an alternating code word in the transmitter, through coding of the base code words, in that mathematical operations are used on them, decoding of the received alternating code word in the receiver, in that inverse mathematical operations are used on the alternating code word, and thus generation of base code words from the received alternating code word, generation of an alternating code word in the receiver, in that the same mathematical operations as in the transmitter are used on the decoded base code words, and comparison of the received alternating code word and of the alternating code word generated in the receiver and generation of a control signal if they correspond.

7. Method according to claim 6, wherein the mathematical operations are logic circuits of the base code words, whereby the alternating code words show a sequence from a mathematical code supply.

8. Method according to claim 6, wherein the control signal is a release signal for a departure blocking device.

9. Electronic safety device substantially as herein described with reference to the accompanying drawings.

10. Method of operating an electronic safety device substantially as herein described, with reference to the accompanying drawings.