EP0265728A2 - Electronic remote control device for the central locking systems of motor vehicles - Google Patents

Abstract

The electronic remote control device works according to the known principle of code advancement, in which a different code word is used after each transmission / reception process. In the invention, the new code word is generated from a stored original code word (1, 19) and the previous code word (3; 17, 21) by logical combination (2, 20) according to a predetermined function . If the code word received and the code word newly determined on the reception side do not match, further code words (CDW x + 1 ..., CDW x + n) are generated in a forward-switching manner. If no match is found, the receiver switches to increased security, in which two immediately successive code words must match.

Description

The invention relates to an electronic remote control device according to the preamble of claim 1. From DE-PS 32 44 049 a remote-controlled central locking system for motor vehicles of the type mentioned above is known, in which the same series of code bits are stored in the transmitter and receiver which represents a number of ordered code words, each of which has several bits. Each time the transmitter is operated, the code bits in the transmitter and receiver are changed by a constant number of bit positions, which corresponds to the length of a code word, switched on. The last word switches back to the first word. Each time it is pressed, it is checked whether the transmitted code word and the current code word pending in the receiver match. If there is a match, the door is opened. With this system, synchronization between transmitter and receiver is absolutely necessary. If this synchronization has been lost, for example by actuating the transmitter outside the range of the receiver (so-called empty actuation), a match can no longer be found. For this purpose, the known system provides that the transmitter and receiver are synchronized to a defined word again by pressing a special key.

This system has the disadvantage that the memory requirement in the transmitter and receiver depends directly on the number of possible combinations. For security reasons, it makes sense to provide as large a number of code words as possible in order to make the cycle in which the code words repeat very long. Otherwise, unauthorized "eavesdropping" on the code could "crack" it too easily. However, the synchronization command is particularly critical for "bugging security". If someone determines the code of the synchronization command without authorization, all he has to do is know the code word that occurs during synchronization and no longer needs to determine the entire bit sequence.

The security advantage of a constantly changing code (so-called code forwarding) is thus considerably weakened again by the need for synchronization, since the synchronization as a result makes the code forwarding invalid. This becomes particularly clear when considering the limit value. You synchronize with every over wear, you can see that changeable code and synchronization contradict each other.

The principle of code advancement is also known from DE-OS 33 20 721. With each word sent, additional information is transmitted there, which contains information about which code number is to be selected from the stock stored in the receiver. Here, too, synchronization between the transmitter and receiver is required. To increase security, it is proposed that resynchronization is only possible in the direction of higher code numbers, which invalidates codes recorded without authorization. Furthermore, the receiver should only accept resynchronization within a narrow interval of code numbers. Here, too, synchronization information is sent over the transmission path and can therefore be recorded.

The problems of synchronization in code advancement are also described in DE-OSes 32 34 538, 34 07 436 and 34 07 469.

The object of the invention is to improve the generic electronic remote control device in such a way that it offers greater security while requiring little storage space for the ordered amount of code words.

This object is achieved in the generic device by the features specified in the characterizing part of claim 1. Advantageous refinements and developments of the invention can be found in the subclaims.

In brief, the invention also works on the principle of code advancement. However, only very little storage space is required, since the individual code words are continuously determined anew from a single original word, which results in an enormous number of possible combinations. Furthermore, the transmitter and receiver need not be rigidly synchronized in the invention. Rather, the receiver automatically synchronizes itself with the transmitter without the need for external measures by the user. In principle, any "pseudo-random generator" can be used as a predetermined function for the logic operation, provided that the "random sequence" is clearly determined, so that two independent pseudo-random generators generate the same random sequence in a transmitter / receiver pair.

With the features of claim 2, the security is further increased. If someone tries to open the lock without authorization using the wrong code, the system switches to increased security. If the probability of finding the correct code word by chance is 1/2 ⁿ , then with increased security it becomes 1/2 ²ⁿ . It should be pointed out that in a sub-combination of claims 1 and 2, the number n (of claim 1) can be zero, with which the increased security of double-word matching is then continuously used.

With the features of claims 3 to 5, the new code words required for code advancement are obtained without all of them having to be stored, the features of claim 5 providing additional security in that the code cannot be "cracked".

With claim 6 one achieves that the transmitter and receiver cannot be influenced by external transmitters in such a way that they are so far apart in their code advancement that they no longer come together.

With claim 7 it is achieved that third-party systems, for example keys of other car brands that work on the same principle, do not trigger code advancement in the receiver, and also the possibilities of providing several functions that are independent of one another, such as Opening and closing the door, switching additional alarm devices on and off, etc. Finally, different key types can also be provided for a transmitter / receiver pair, as is already common with mechanical car door keys. For example, one key only closes the doors, but not the trunk, a second key only closes the trunk but not the doors and a third key closes all the locks.

With claim 10 one achieves automatic resynchronization in the complete code stock even if the transmitter and receiver are separated by more than m + n (claim 2) steps. With the features of claims 1 and 2, the device aborts code advancement after m + n advancements. The user must then open the door with a mechanical key. In order to be able to achieve synchronization even in such cases, for example due to a power failure in the transmitter or receiver, the full code stock is run through if two criteria are fulfilled (e.g. open lock and switched on ignition). if in a longer time, the synchronous run between transmitter and receiver is restored.

• Fig. 1A ein Blockschaltbild des Senders;
• Fig. 1B ein Blockschaltbild des Empfängers;
• Fig. 2 ein Kreisdiagramm der Codefortschaltung zur Erläuterung der Arbeitsweise der Erfindung.
• Fig. 3 ein Flußdiagramm zur Erläuterung der Funktions­weise des Empfängers;
• Fig. 3A einen Ausschnitt des Flußdiagramms der Fig. 3 mit einer zusätzlichen Variante zur automatischen Nachsynchronisation; und
• Fig. 4 ein Diagramm zur Erläuterung des Übertragungs­formates der Code-Wörter.

In the following an embodiment of the invention is explained in more detail in connection with the drawing. It shows:

• 1A is a block diagram of the transmitter;
• 1B is a block diagram of the receiver;
• Fig. 2 is a pie chart of the code advance to explain the operation of the invention.
• Fig. 3 is a flow chart for explaining the operation of the receiver;
• FIG. 3A shows a section of the flowchart of FIG. 3 with an additional variant for automatic post-synchronization; and
• Fig. 4 is a diagram for explaining the transmission format of the code words.

• a) Kennzeichnung von Schlüsseltypen, die unterschiedliche Schließfunktionen haben, w.z.B. nur Türschlösser, Tür­schlösser und Kofferraum etc.
• b) Systemkennzeichnungen w.z.B. Automarke, Schlüssel­system
• c) Auszulösende Funktionen w.z.B. Öffnen/Schließen etc.
• d) Steuerbits
• e) Parity-Check-Bit, etc.

The transmitter shown in FIG. 1A contains a first memory 1, in which an original code word is stored, which is referred to below as a "key code word". This memory 1 can be in the form of fixed wiring, but a programmable memory, in particular an EEPROM, is preferred. In principle, the length of this key code word is arbitrary. To explain a specific exemplary embodiment, it is assumed that this key code word is 32 bits long. It is organized in such a way that 24 bits of it are the actual key code word that is individually assigned to each transmitter / receiver pair, while the remaining 8 bits are so-called system bits that can be used for various differentiations, such as:

• a) Identification of key types that have different locking functions, e.g. only door locks, door locks and trunk, etc.
• b) System markings such as car brand, key system
• c) Functions to be triggered, e.g. opening / closing etc.
• d) control bits
• e) parity check bit, etc.

The memory 1 is connected to a circuit 2 which generates a current code word (hereinafter referred to as CDW) from the key code word according to a predetermined logical function, which is stored in a further memory 3. In a preferred exemplary embodiment of the invention, the circuit 2 is implemented by a chain of exclusive OR gates which, according to the method of the generator polynomial or polynomial ring, consists of the key code word alone or the key code word and the previous one CDW generates a new code word. To explain the method of the polynomial ring, let us first choose a simplified example in which the CDW is only determined from the key code word.

An initial word (key code word) "0110" is stored in a feedback shift register with 4 bit digits. An exclusive-OR gate is connected between the first and the second bit position (seen from the right), which links the current bit positions of the first and second bits with one another and writes the result of the combination into the first bit position, then all Bit positions are shifted one place to the right and the first bit position moves to the fourth bit position. This results in the following sequence:

Bit position: 4321

• CDW 0 0110
• CDW 1 0011
• CDW 2 1000
• CDW 3 0100
• CDW 4 0010
• CDW 5 0001
• CDW 6 1001
• CDW 7 1101
• CDW 8 1111
• CDW 9 1110
• CDW10 0111
• CDW11 1010
• CDW12 0101
• CDW13 1011
• CDW14 1100
• CDW15 (0) 0110
• CDW16 (1) 0011 etc.

The polynomial ring has 15 different states. In this example, the originally saved key code word changes continuously. If you know the logical combination or the formation law of the "sequence", you can determine the next CDW from any CDW. This code can therefore still be easily decrypted. From the table above it can also be seen that from CDW 2 to CDW 5 only one 1 traverses from left to right. If someone unauthorizedly records CDW 2 and CDW 3, it is relatively easy to infer CDW 4 and CDW 5. The code is therefore particularly easy to "crack" at certain execution points of this code advance. Therefore, the invention further provides that the logic operation is only carried out if a certain bit, which acts as a control bit, has a logical 1. For example, you select the highest-order bit (bit position 4 in the table above). Although this shortens the polynomial ring, it is more difficult to find out the law of education with which one can infer from one code word CDW x to the following code word CDW x + 1.

A much better variant of the principle of the generator polynomial is used in the exemplary embodiment in FIG. 1: If the key code word is unchangeable, there is bit-by-bit exclusive OR operation between the bits of the key code word and those of the previous CDW. Even if you know the educational law of the episode and the previous CDW, you cannot determine the new CDW without knowing the key code word.

According to one embodiment of the invention, this is carried out in such a way that the exclusive OR operation with the corresponding bit position of the CDW is carried out only at the points where the key code word has a logical 1. An example of a 16 bit long word should clarify this:

Key code word: 1010100011100110
Last CDW (x-1): 0110010101001011
XOR wo Key = 1: xxx xxx xx
Key (XOR) CDW: 1100110110101101
Move one position to the right = New CDW (x): 1110011011010110

It can be shown that this continuously changes the CDW. This type of link is based on certain key code words also go through all possible combinations before one of the possible combinations is repeated for the second time. With a length of key code word and CDW of 32 bits, there are 2³² = 4.29 × 10⁹ possibilities. With some key code words (eg: 000000 .... 00) or types of logical combination, the "polynomial ring" does not go through all possible combinations, the polynomial ring is therefore shortened, which is of no importance for the basic principle of the invention. After the logical combination has taken place, the CDW in the memory 3 is then shifted by one bit position, the last bit then being shifted to the first position. This is represented by line 4. These processes take place under the control of a control unit 5, which generates the required clock frequencies and the individual control signals. If the user presses a button 6, a transmission cycle is triggered, in which a new CDW is generated in the manner described, which is then read out serially from the memory 3 under control by the control unit 5 and via a coder 7 with a modulator and amplifier into one Transmitter unit 8 arrives, which here is a light-emitting diode that shines in the infrared range.

• 1) Die Systembits werden zeitlich vor dem CDW gesandt.
• 2) Die Systembits werden zeitlich nach dem CDW gesandt.
• 3) Die Systembits werden teilweise vor und teilweise nach dem CDW gesandt.
• 4) Die Systembits werden im CDW verschachtelt gesandt.

In one variant of the invention, the CDW is formed only by linking to the actual key code word, while the other system bits are each sent unchanged, for which several variants are possible:

• 1) The system bits are sent before the CDW.
• 2) The system bits are sent in time after the CDW.
• 3) The system bits are partly sent before and partly after the CDW.
• 4) The system bits are sent nested in the CDW.

In the exemplary embodiment in FIG. 1A, further switches 9 and 10 are connected to the control unit, via which other functions, e.g. Opening or closing a door etc. can be selected. If one of these switches is actuated, only one or more system bits are changed, while the rest of the sequence is carried out unchanged.

The light emitted by LED 8 is transmitted in the form of coded light pulses. For example, a pulse-distance modulation can be selected in which the distances between two adjacent light pulses are of different lengths at a logical 1 and a logical 0 (cf. FIG. 4). Of course, other known modulation methods can also be used. These light pulses are detected in the receiver (FIG. 1B) by a photo sensor 11, decoded and amplified in a pulse processing unit 12 and then, under the control of a control unit 14, first checked whether the pulse sequence can be a valid CDW in terms of its format . The following are checked, for example: number of bits, minimum length of a pause after the last received bit, match of certain system bits, etc. This check is carried out in a unit 15. If the test result is positive, the CDW received is written into a receive buffer memory 13 (I-buffer). Under the control of the control unit 14, the next CDW is then determined in the same way as at the transmitter and written into a temporary memory 21 (T-buffer). Then the content of the T-buffer 21, that is to say the current code word generated in the receiver and the received word stored in the I-buffer 13, that is to say generated by the transmitter, are compared with one another in a comparator 18. If these two words match, it will reported to the control unit 14, which emits an actuation signal, for example a door opening signal.

To generate the current CDW in the receiver, a memory 19 for the key code word is also provided there, as well as a logical link 20 (here: exclusive OR link). The basic procedure for generating the current CDW in the receiver corresponds to that of the transmitter.

In normal operation, the transmitter and receiver switch one code word each time they are pressed. You can also say they run in sync.

• a) Betätigung des Senders und damit Code-Fortschaltung außerhalb der Reichweite des Empfängers (sog. Leer­betätigung)
• b) Fortschalten des Empfängers durch einen systemgleichen Fremdschlüssel (z.B. auf einem Parkplatz)
• c) Fortschalten des Empfängers durch unbefugte Öffnungs­versuche
• d) Stromausfall im Sender oder Empfänger und damit Rücksetzen flüchtiger Speicher.

However, the sender and receiver can now "get out of step", for example due to the following reasons:

• a) Actuation of the transmitter and thus code advance outside the range of the receiver (so-called empty actuation)
• b) Advancing the recipient using a foreign key of the same system (e.g. in a parking lot)
• c) The receiver is switched off by unauthorized attempts to open it
• d) Power failure in the transmitter or receiver and thus resetting volatile memory.

The most common case in practice is to empty the transmitter, which should be given special attention here. The relevant features of the invention are to be clarified with reference to FIG. It is assumed that the transmitter and receiver are in their original state (CDW 0) have run in sync to any CDW x. If the transmitter is actuated empty, the transmitter is then on CDW x + 1 while the receiver is still on CDW x. The transmitter is therefore one (or more) steps ahead of the receiver. If the receiver, which is still on CDW x, now receives the CDW x + 1, the comparator 18 detects a mismatch. So the lock is not opened. Thereupon, however, the control unit 14 triggers a code advance in the receiver, so that the next successive code words are progressively determined there, however at most a predetermined number n, that is to say the code words CDW x to CDW x + n. In a practical embodiment, one will choose n on the order of ten steps. If agreement is found within these n increments (code words CDW x to CDW x + n) with the received code word (here: CDW x + 1), the actuation signal is generated and the CDW, in which agreement is achieved, is generated in the receiver was stored (here CDW x + 1) as a valid code word for the next actuations in a memory 17 (N-buffer). As long as no match is found, the CDW currently determined in the transmitter is only stored in the T-buffer 21. The content of the T buffer 21 is only transferred to the N buffer 17 if there is a match. However, the received CDW can also be transferred from the I-buffer 13 into the N-buffer 17.

It can be seen that in this case the receiver recalculates so-called lost code words, so that the transmitter and receiver synchronize themselves automatically, without synchronization pulses, which can be recorded without authorization, having to travel over the transmission path. The user is not aware of this synchronization.

Now it can happen that the transmitter has experienced more than n idle operations. No match is found within the n CDWs recalculated by the recipient (CDW x to CDW x + n). According to a further feature of the invention, the receiver then switches to increased security, in which two immediately successive CDWs must match.

A number of m further code words (i.e. CDW x + n to CDW x + n + m) are determined, where m is greater than n (e.g. m = 256). If the receiver is in this operating state, the user must press his button twice on the transmitter. The possible combinations then correspond to those of a 2 × 32 = 64 bit long word, i.e. approx. 1.8 × 10¹⁹ possibilities. If the double match is found within the sequence CDW x + n to CDW x + n + m, the actuation signal is generated again and the last CDW received is transferred to the N-buffer 17. If, on the other hand, no match is found here either, the attempt to open the door has failed, the lock then has to be opened with a mechanical key, for example, and the CDW received last is transferred from the I-buffer 13 to a further reception memory 16 (X-buffer).

• 1. Türschloß (mit mechanischem Schlüssel geöffnet) und
• 2. weiteres Kriterium wie z.B. Zündung des Autos einge­schaltet.

Automatic resynchronization can therefore only take place in the sectors n and m of FIG. 2 according to the features of the invention described so far. If the power supply in the transmitter or receiver fails, depending on the previous history, ie the number of previous operations, these can also be so far apart that they no longer lie in the sectors mentioned. According to an embodiment of the invention, which is explained in more detail in connection with FIG. 3A, a resynchronization can also take place. For security reasons against unauthorized opening Normally, the post-synchronization should only be carried out in a narrow range (n + m), so that an unauthorized person with a function generator does not simply go through all the options. Also, the numbers n and m should not be chosen too large, so that the recipient is not blocked too long in the event of unauthorized attempts to open them. However, in order to be able to achieve a re-synchronization even in the case described, the invention provides that the number m is unlimited if two criteria are met. These criteria are preferably:

• 1. Door lock (opened with a mechanical key) and
• 2. Another criterion such as ignition of the car is switched on.

If the door lock cannot be opened electronically despite the transmitter button being pressed twice, the user must therefore unlock the door lock mechanically, switch on the ignition and then press the transmitter button again. The receiver then calculates all code options until a match has been found, in extreme cases the full circle of FIG. 2. If one calculates with an average of ten actuations of a car lock per day, only 36500 code increments are carried out in the course of ten years. Compared to the 4.2 × 10⁹ theoretical code increments for a 32-bit CDW, this is a relatively small number. Even after ten years of operation, the receiver and transmitter will still be relatively close to zero CDW. So that the full circle of FIG. 2 does not have to be calculated now, it is advisable to reset the transmitter to its original state by briefly removing the battery, that is to say the state CDW zero. Since the receiver has only made the relatively small number of 36,500 code increments, the synchronization is found faster than if the full circle in FIG. 2 is calculated.

It can now also happen that the described n and even the steps n + m have expired in the receiver by a third-party transmitter. However, since no opening was triggered by this third-party transmitter, the last match word, ie the word CDW x, is still in the N-buffer 17. However, the receiver has switched to the match mode of two consecutive words. If the right transmitter sends the CDW x, the door will not open yet. The user must then operate the transmitter a second time. Then CDW x and CDW x + 1 will match as a pair, the door opens and the CDW x + 1 is transferred to the N-buffer 17.

According to a further variant of the invention, the number n can also be set to "zero". In this case, increased security is always used. It can then also be provided that when the button 6 (FIG. 1A) is pressed once, two successive CDWs are always determined and sent out.

According to a further feature of the invention, both memories 1 and 19 for the key code word are designed as EEPROMs (electrically erasable, programmable memories). On the one hand, this has advantages in terms of production technology, since all transmitters and receivers can be constructed identically in terms of hardware and the key is only programmed into a transmitter / receiver pair after the hardware has been completed. On the other hand, this is also an advantage if a transmitter (key) is lost. The entire system then does not have to be replaced. Rather, it is enough to buy a new transmitter (key) and reprogram the receiver. Of course, this is only possible with the door open. A switch 14 "switches the receiver to the" learning phase ". The new The transmitter then sends the key code word once, which is then written into the key memory 19 of the receiver in this learning phase.

The flow chart of FIG. 3 again illustrates the process steps, the corresponding reference numerals of the steps also being entered in FIG. 1B. Upon receipt of a formally valid received code word, the current CDW (N-buffer 17) is pushed into the T-buffer 21 in step 22. It is then checked in step 23 whether the system is based on simpler security or higher security. If the focus is on simple security, the content of the T buffer 21 is logically linked to the content of the key memory 19 in step 24, the result being the new CDW that is stored in the T buffer 21. It is then checked in step 25 whether this new CDW matches the content of the I buffer 13. If this is the case, the desired function is triggered via step 26 and the content of the I buffer 13 is transferred to the N buffer 17. If, on the other hand, the test in step 25 yields a negative result, a query is made in step 27 as to whether the number of n attempts has already been carried out. If the result is negative, the loop goes back to step 24; if the result is positive, step 28 switches to increased security.

If the system is more secure when a valid code word is received, step 23 branches to step 29, where it is checked whether the content of the T-buffer 21 matches the content of the I-buffer 13. If this is not the case, a new CDW is determined in step 30, this process being repeated up to m times in accordance with step 31. If these m attempts do not match according to step 29, the content of the I buffer becomes 13 transferred to the X buffer 16. If, on the other hand, the check in step 29 shows a match, then the next CDW is calculated in step 32 and a check is carried out in step 33 to determine whether this new (second) CDW also matches the content of the I buffer 13 transmitted in the second transmission step. If this is the case, the desired function is triggered again and in step 26 the system switches back to simple security and finally the content of the I-buffer 13 is also written into the N-buffer 17.

FIG. 3A shows a section of FIG. 3 with the additional variant of resynchronization in the complete code stock. If it is found in step 31 with the higher security that the number of m attempts has expired, then the code advance would be terminated according to the variant in FIG. 3. It would no longer be possible to open the door. According to the variant of FIG. 3A, it is checked in step 35 in this case whether the door is open. If this is not the case, the code advance is canceled again (step 34). If, on the other hand, this is the case, then a check is carried out in step 36 to determine whether the further criterion is met, for example if the ignition is switched on. If this is not the case, the process is terminated again (step 34). If this is the case, the system switches back to step 29. The loop of steps 29, 30, 31, 35, 36 is then continued until a match has been reached. If the pair of transmitters and receivers is working properly, then a synchronous run will certainly be achieved again.

Fig. 4 illustrates the transmission format. After pressing button 6 on the transmitter, a pre-pulse is sent out as a so-called wake-up pulse, which the receiver in Willingness to receive. The actual data is then sent out in the form of the code word (FIG. 4a). The data is organized in such a way that eight system bits are sent first and then the actual CDW (Fig. 4b). The logical states "1" and "0" are represented here by a so-called pulse distance modulation. For each bit, several individual pulses in which the light-emitting diode 8 is switched on are emitted, specifically as shown in FIGS. 4c and 4d, at the beginning and at the end of a bit, a constant number of pulses, for example 6. The time interval between the Pulse groups at the beginning and end of a bit then determine whether the bit is a logic "1" or a logic "0".

Finally, it should be pointed out that the two variants of the "generator polynomial" described above do not constitute a conclusive list. Of course, other link options can also be used. For example, all bits of the key code word and the current CDW can also be linked to one another and not only those bits in which the key code word has a "1". However, in order to keep the number of different coding options as large as possible, care must be taken that such encryption is chosen that no shortened polynomial rings occur or only slightly shortened polynomial rings.

The described method of the generator polynomial can be viewed more generally as generating a "pseudo-random sequence". It is clear that all other known methods for generating "pseudo-random sequences" can also be used in the invention, provided that it is ensured that - in the transmitter and receiver - starting from a and the same key code word the same "pseudo-random sequence" is generated.
It is also important to ensure that the cycles for the n and m steps are not too long, so that the receiver is not blocked for too long by third-party transmitters, and thus the probability that an unauthorized person with a function generator that plays through all bit combinations, the Door does not open, does not become too small. For this purpose, it can also be provided that the receiver is blocked for a predetermined period of a few seconds after each CDW received, which increases the period for playing through all combinations to several years. In the case of resynchronization through the entire code stock (FIG. 3A), however, no artificial time delay should be provided.

The particular advantages of the invention are to be emphasized: Code words of almost any length can be provided, the storage space requirement nevertheless remaining within narrow limits. In the subject of the prior art, not all code words have to be permanently stored;
Even if someone knows the algorithm for determining a new code word and has recorded previous code words without authorization, he cannot determine the next code word because he does not know the key code word. However, he cannot record this without authorization, since it is not transmitted via the "transmission path";
the receiver automatically synchronizes itself with the transmitter without the need for commands that are sent over the transmission path and thus recordable. This eliminates the disadvantages of synchronization accepted in the known code update;
the security against decryption of the code is extremely high;
Empty operation of the transmitter and operations of the receiver by third-party transmitters show no consequences that are noticeable to the user;
if a transmitter (key) is lost, the receiver can be easily adapted to a new transmitter without reducing security.

All of the technical details shown in the claims, the description and the drawing can be essential to the invention both individually and in any combination with one another.

Claims (10)

1. Electronic remote control device, in particular for central locking systems of motor vehicles with
- a key transmitter and
- a receiver working as a lock,
- The transmitter emits a code word in the form of coded signals (bit sequence) when actuated, and does another per actuation res code word from an ordered set of code words,
the receiver, upon receipt of a formally valid word, in the same way provides a comparison code word from the ordered set of code words for comparison with the code word sent by the transmitter and generates an actuation signal if these words match,
characterized by
- That in the transmitter and in the receiver in the same way, starting from a common original code word with each advance, a new code word (CDW x) is generated by logic operation (2, 20) according to a predetermined function and
- That the receiver in the event of a mismatch between the received code word and the comparison code word forwards and onwards generates further code words (CDW x + 1 ..., CDW x + n) and compares them with the received code word, but doing so carries out at most a predetermined number n of increments and comparisons. 2. Remote control device according to claim 1, characterized in that the receiver in the event of a mismatch during the number n increments and comparisons for the reception of a second code word, a further number m of successive comparison code words (CDW x + n + 1 ... , CDW x + n + m) and compares whether the two code words received immediately after one another match with two immediately successive comparison words, the number m being greater than the number n. 3. Remote control device according to claim 1 or 2, characterized in that the generation of the successive code words in the transmitter and in the receiver each by a pseudo-random sequence and in particular by an exclusive OR operation (2, 20) of individual bit positions of the original Code word is done. 4. Remote control device according to claim 3, characterized in that in the transmitter and in the receiver the fixed predetermined original code word (key code word; memory 1, 19) and the current code word (CDW x; 3, 21) are stored, the next following code word (CDW x + 1) being determined in that those bit positions of the current code word (CDW x) which have a logical "1" with the corresponding bit position of the fixed code Word (key code word) are ORed exclusively (2, 20) and then all bits of the current code word are shifted by one bit position, the last bit position being shifted to the first bit position. 5. Remote control device according to claim 4, characterized in that the exclusive-OR operation (2, 20) is only carried out when a predetermined bit position (control bit) carries a logical "1", while at a logical "0" this control bit only the shift is carried out until the control bit has a logic "1" or until a predetermined number of shifts has been carried out. 6. Remote control device according to claim 5, characterized in that the highest-order bit position is the control bit. 7. Remote control device according to one of claims 1 to 6, characterized in that the current comparison word at the n and the m increments and comparisons is stored in a temporary memory (21) and only if they match the code word (s) received new code word is transferred to a further memory (17). 8. Remote control device according to one of claims 1 to 7, characterized in that the code words have one or more bit positions which are unchangeable and bypassing the exclusive-OR link (2, 20) directly to a transmitting device (7, 8) and the comparator (18) are supplied. 9. Remote control device according to one of claims 1 to 8, characterized in that the memory (1, 19) for the original code word, at least in the receiver, is an electrically erasable, programmable memory (EEPROM). 10. Remote control device according to one of claims 2 to 9, characterized in that when the lock is open and an additional condition is fulfilled (e.g. when the ignition of a motor vehicle is switched on) the number m is unlimited.

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