1.

and may be avoided. The solution described in US Patent 4,584,570 has the same problem. US Patent 4,494,114 uses a code which may be entered manually each time something unforeseen has occurred, e. g. that the power has been disconnected. Firstly, this is less secure than the time lock system, and in addition it will require entering the code quite often. The code must therefore be kept in the vicinity, which is a weakness of the system. For the present invention it will not be necessary to remember a code, or to enter the code manually as is described in patent applications No GB 2,229,025 and PCT/SE93/00008. Neither will it be necessary to close down the equipment after e. g. the power cord is disconnected. It is the absence of code over time that will result in the sabotage of the equipment. It is thus an object of this invention to provide a system for securing of especially electronic equipment by transferring a code to the equipment making it impossible to copy the necessary code and making use of the equipment impossible if the necessary code is not received. This object is obtained using a system as described above and being characterized as given in the enclosed claim 1. The idea is thus to combine the principles mentioned above so that the correct code must be present all the time to allow functioning of the equipment and so that it is impossible to steal the code without being present at the scene for a long time. The code may be transmitted from a hidden location or even better e. g. through a telephone or cable TV network so that the"key"physically will have to be stolen from a telephone central or similar. For electronic equipment it is, according to a preferred embodiment of the invention, possible to set the equipment sufficiently out of function to make it practically impossible to bypass it. This will be even more efficient with the miniaturisation of electronics and development of microelectronics (ASIC). This is especially relevant in the cases in which modules of the ASIC itself is bought from suppliers. This idea may be realized by selling a specialized module for theft securing of electronic equipment. The present invention supplements to a large degree other described invention and may function together with them or other known not patented techniques for burglar alarms or retracing of stolen equipment. The present invention will normally be able to cover the need for preventive theft securing and a coupling of the legitimate owner to the equipment, as it is not possible to remove the code as it is with a serial number. If needed functions such as sirens, silent alarms, retracing or similar may be extended into a total system. The invention will be described below with reference to the accompanying drawings, which by way of example illustrates one possible embodiment of the invention.

2.

Figure.

3.	shows a circuit according to the invention mounted in a circuit to be protected.

4.

Figure.

5.	shows a circuit according to the invention mounted as a module in a larger circuit (ASIC).

6.

Figure.

7.

shows a circuit diagram illustrating an embodiment of a control circuit according to the invention. In the equipment 27 to be protected a small electronic circuit 21 is positioned which listens for a code sequence sent through a chosen line 22 (possibly through the telephone line) or through the power supply (especially preferable in low voltage local supplies in cars or boats or similar). The code sequence is relatively long, e. g. 47 hours. Thus it is impossible to received the complete code in under 47 hours without physically stealing the"key" transmitting the code as well. The key is either hidden (anywhere in the power supply net) or is positioned in a place demanding an extra breakin, e. g. in a telephone central. Even if the means for transferring 22 is indicated as electrical conductors 22 the code may also be transferred using optical signals or with radio signals. The circuit in figure 1 also comprises clocks 23 and means for signal transferring 26, wherein the control circuit e. g. may break or disturb the signal path to hinder the use of the equipment. The circuit listens for the code sequence and if less than e. g. 90 % of the sequence during 24 hours the equipment is"sabotaged"for a period of e. g. 16 hours before it starts listening for the code again. Until it has received 905 of the code during 24 hours the equipment will be useless for the thief. The circuit runs on an internal clock (synchronised with the equipment to be protected). Thus a new code sequence can not be tried effectively more frequently than once every 24 hours. With a total code length of approximately 1 kbytes it will take more than 10 years to find the correct code by trial. The code is sent in small packages e. g. of 4 bit each third minute. The content of these packages may, in addition to the code itself, include additional information, such as where in the code sequence is belongs, or possibly information on the code as a whole which e. g. may be used to discover errors or holes in the sequence. The packages may also comprise commands to the security circuit, such as instructions deactivating the theft security if maintenance is to be performed. It is preferable to use a large distribution of the sent code packages. It is also preferable to secure against transmission errors. Both for telephone networks, cable TV and power networks a signal frequency of app. 1 kHz is preferable to ensure secure transfer. It will be natural to use e. g. an 8 bit sequence in each transmission wherein the first four bits are identification and synchronisation bits (no code information) followed by 4 variable bits. A new package is sent each 3rd minute. After approx. 48 hours a code sequence of 1 kbyte may then be completely transferred. It is a point that it should not be tested on a short, exact code, but on the continuity in a long code sequence with a certain tolerance for errors both to make it difficult to recognize the correct code and to tolerate transmission errors without forcing a"sabotage". Less restrictions may be set shorter availability (telephone lines may e. g. be inaccessible for signalling). All the equipment in one house may be secured using the same key. New equipment is zeroed from the manufacturer and is taught the local code (key) in the course of 2 to 7 days. There is no need to do anything other than plug the equipment to the power net, telephone net or another net or it may be an automatically activated cable less net. The important aspect is that the activation does not cause any problems for the user. The equipment may be moved as any other equipment, as long as one restores contact with the code after being moved. No intermissions will be experienced when moving usual equipment. Automatic deactivation when the power is cut may be chosen as an option, but there will be few type of use requiring it. Computers and other equipment in which securing of data is more important than user friendliness will probably be the only exception. Deactivation is employed by cutting out chosen windows in the code. This may for example be done in one of the following ways, depending on requirements for being user friendly, security and cost: 1. The equipment must be disconnected from the key in 8 hours, connected in one hour and then disconnected completely.

8.

2 The equipment must be disconnected in two periods on 16 hours each with a period of 8 hours between them. In the end the equipment must be connected in one hour (the disconnecting process takes 41 hours, or typically two work days. If the equipment uses e. g. a telephone cable to be connected to the key the telephone plug is disconnected. If the power supply is used it will work because the theft security circuit will know the code sequence and thus may read where in the code sequence it is (and thus the length of the time window) when the power returns. It is natural to have, e. g. a time window of 2 hours where deactivation available. If it takes more time than the window full activation is reestablished. This means that a new learning sequence is not necessary. It is of course not certain that one needs to use the length of the code sequences indicated here. It may be sufficient in practice with a couple of hours ro make it uninteresting for thieves to steal the device. It then opens for a possibility for faster activation and deactivation. It is thus possible to use a service at the"key supplier" (usually the telephone operator). It will be possible to call in a message requiring that the theft security is deactivated at a until a certain time, the key supplier then performing the deactivation process centrally. Then all equipment with the same key is deactivated in the same period. Note that et still is a time lock. Authorization may be given with a personal code. This type of deactivation may for increased security also demand that it is performed from the same line as is used for sending the code. Thus no one from outside may order a deactivation, at the same time as the operation of each user is simplified somewhat. If this type of central deactivation is provided is a question of security level. The equipment may be deactivated in a number of different ways, depending on the equipment, e. g. : 1. By breaking a line for signal and/or power transmission, which is well known if the security circuit constitutes a part of an ASIC in the equipment, so that it is not possible to connect around the line break.

9.	2 Short circuit between two lines, which makes the search for the security circuit difficult. This may e. g. be done by short circuiting a system clock in parts of the equipment, if this may be done without harming the equipment permanently.

10.

3 Generating digital noise pulses, for example short sequences 115 seconds each minute from a data bus. The noise source will be difficult to localize and may be integrated into an otherwise difficult exchangeable component in the circuit. In practice the sabotage for example may hinder that the channel controller on a TV functions sp that only one channel is available or that all communication with the outer RAM in a PC is blocked. For simpler equipment, e. g. a PLL radio digital noise may be sent to the tuner. If the equipment need reparation or maintenance it may be done in the following ways: 1. The sabotage may be performed in such a way that it does not make it impossible to perform usual maintenance, but makes normal use impossible. For example the one available TV cannel may be used during service.

11.	2 The disturbance is limited in time, e. g. 15 seconds each minute giving 45 seconds for service.

12.

3 The owner may deactivate the security circuit before the equipment is delivered for service. It is important that the theft security is installed in such a way that t is difficult or impossible to bypass. Modern electronics opens for these possibilities. The package density for modern electronics is so high that it demands very sophisticated equipment to modify the circuits. There is especially one development coming forth which provides good possibilities for our technology. So called IP is a development in which large parts of the system is integrated on a silicon chip (ASIC). In stead of buying different ASICs and standard equipment from different suppliers and put them together on a printed circuit board the functionality is bought, (almost like software) and printed into parts of the ASIC. Thus functionality developed and sold by different companies are integrated in the same ASIC. The total system will the often be constituted by 15 ASICs and some other components around them, and they are unique for the product, not sold separately. An example of such a circuit is shown in figure 2. Figure 2 shows a theft securing module 21 with a signal path 22 for receiving a key. The rest of the circuit 24 comprises also a clock 23 coupled to the security module and a number of other circuits which for example may comprise modules 25 for computing, picture compression, frequency synthesising etc. It is sufficient to provide the theft securing module in an ASIC in the system. If the manufacturer is careful he also lay this signal in through a deeper layer in the circuit board so that it is not possible through inspection to see which ASIC contains the theft security. It is also possible to enclose a theft security e. g. mounted in a multichip module (e. g. the Pentium Pro processor contained two chips in the same package). Last it is possible to enclose the theft security in a designated package on a circuit board. If, for example, modern surface mounted circuits are employed it is difficult to make modifications without advanced equipment and with e. g. BGA (Ball Grid Array, closely distributed solder balls under a chip) it is very difficult to remove the theft security circuit, especially if more signals are sent through the theft security circuit. It may also be possible to provide the theft security according to the invention in existing equipment, but this will be easier to bypass. Of course several theft security modules may be mounted in the same equipment to improve the theft security. Also not that if it will not help the thief to find/follow the signal from the key and cut this when the theft security module has learn the code. The theft security module may be implemented in a number of ways which are not essential for this invention, but the following solutions may be utilized: A non erasable memory of any available type, preferably Flash or EEPROM, to keep the key (code). A sufficiently large buffer to hold the last version of the sent code, preferably in normal static RAM with one week holding time. Timing recovery using digital down converting of the system clock, if such is available. In ASIC design the down converting number is hard programed in ROM, while a more general module must contain a detection circuit to recognize a system clock. Adaptation of the input signal to tolerate being coupled to e. g. a telephone line. "Sabotage modules"as indicated above. The different circuits in the system according to the invention may be made in a number of different ways, depending on the equipment that is to be protected and the available equipment. The transmitter may be of any commercially available type, and may also be integrated in other equipment, such as telephone centrals or radio transmitters. The transmitter may also comprise secondary units for transferring the signal to the protected equipment. Such a transfer unit may be positioned anywhere in the system as long as it does not store any essential parts of the code. The transfer unit may for example be a local radio receiver receiving and transmitting the code further to each local unit with electrical signals. A possible embodiment of the control device adapted to be positioned as a module in a larger system, such as described with reference to figure 2, is illustrated in figure 3, in which the functionality of the circuit and each of the components may be described as follows: 1. A system clock is provided from the circuit the module is a part of. This is distributed further to where it is required in the rest of the circuit for logical operations.

13.	2 Clock division, a counter reducing the systems clock frequency to a slow, e. g. 10 kHz, system clock for the theft security.

14.

3 Clock phase restorer cooperating with 22 to synchronise the theft security clock with the signal bit stream from the input 6 for the code signal. The clock division starts during startup with a random phase, but is adjusted by zeroing from the clock phase restorer when synchronisation with the bit stream is found.

15.

A first down division register constituting a non volatile register being used as divisor in the down division circuit. Normally this is given as the system clock is exactly determined. In that case this register may be realised as ROM/PROM. the system clock is not determined, for example in that the module is used in a standard component which is incorporated in a for the manufacturer unknown total circuit, the realization must be in FLASH/EPROM or another writable technology.

16.	A second down division register being used is store the synchronising information for down division of the system clock to the bit stream (counting numbers for how long a bit is and for"blanking"period at input 6). In technical realization this will correspond to the first down division register.

17.	Input for the signal bit stream. Signalling is described another place, for example the signal may contain four predetermined and four variable code bits with approx. 1 kHz signalling frequency and pauses of 3 minutes.

18.	Window generator clocks in the signal from the input 6 and defines a time window in which a signal is search for. What happens on the input 6 outside the specified time windows is neglected.

19.

Introduction detector clocks in 10 samples of the bit stream, recognizes bit transitions, which in reality may be combined with the abovementioned restoration of clock phase 3, where a introduction sequence, e. g. 1010 which gives good possibilities for synchronising and when at least 5 subsequent receptions are alike the bit is granted as being sampled.

20.	Intermission detector controlling that the right 4 bits have been received. If it is not the case logical intermission signals are set so that synchronisation should not occur.

21.	Code restorer is realized in the same way as the introduction detector 8, but is zeroed when the intermission signal from the intermission detector 9 is true.

22.

Raw code register storing codes found in the code restorer 10 sequentially as long as intermission is not signalled from 9. At intermissions new code is not stored, but the memory is organized so that intermissions are marked, e. g. by 0000. The code is stored cyclic. The realization of should secure that the code is held in static RAM for several days for example with a condenser backup, but this is not critical. An alternative realization is to used/expand the introduction sequence with addressing into the code sequence, which is more suitable for equipment being on/connected in short periods at the time.

23.	Code sorter going through the signal stream stored in 11 as long as the lock activator 13 signals that the apparatus is in learning mode and when the complete code in duplicate is found this is transferred to the key 15 and the lock activator 13 is turned.

24.

Loc activator realizes in a rewritable nonvolatile register, e. g. FLASH. This may in addition contain a "timer"which demands that the equipment is disconnected for a number of cycles of the theft security system, clock, e. g. realized as a counter. The most significant bits in the counter are realized in a nonvolatile register.

25.	Code comparator being activated when the lock activator 13 is turn and is used to compare the raw code with the key.

26.

It may be compared sequentially 8 by 8 bits. When 8 corresponding bits are found one bit error is allowed in the next 24 bit, and so on until the whole sequence is run through. If the limit for bit errors is exceeded the code is shifted relative to the key and tried again. If more than 5 sequences of the 8 bits which at any time is in the raw code register contains errors (more than errors in one bit) or at least two different continuous sequences of 80 bits does not exist when there are more than 400 bits in the raw register a disconnection signal 16 is activated. New code is checked when it is added. There will be less than 524288 comparisons per 8 bit, complete set, for each new bit sequence, which arrives each 6 minute, and with 10 kHz clock this is sufficient time and statistically far less comparisons will be necessary.

27.	15 The key is realized in a rewriteable nonvolatile register, e. g. of the FLASH type.

28.	The disconnection signal is a logical signal adapted to disconnect the circuit.

29.

Zeroing logic containing essentially the key being used to check that the time rule is followed. It is checked against the last content of the raw register, including intermission detection. Received code must agree with the specified intermissions in the code sequence. Alternatively a counter may be used to keep order in the time and a mask relative to intermissions detected in the intermission detector 9.

30.

Zeroing device adapted to secure that the content of key 15, and possibly the down division registers 4,5 as described below with possible extensions, see the clock timing restoring, is reset when the equipment is moved and thus is performed through signals from the zeroing logic 17. Zeroing of all the registers physically is not necessary before the systems power supply is cut. The zeroing device must store the signal if this shall be performed, and when the apparatus receives the supplied voltage again the zeroing may be completed. This because it may demand some energy to delete non volatile registers.

31.	The system as described above may be extended in a number of ways, depending on the equipment and demands for safety and function, for example by implementing the following:.

32.

A clock timing restorer may be used when the circuit does not operate on a determined clock frequency. A table over preset down divisions covering the upper to the lower operation frequency with 25% increase in the division number between the table value is searched cyclic until a synchronising signal is found. These are transferred to the division registers 4,5. For fine adjustments signals from the clock phase restorer 3 are used. Starting of a sequence is performed when the clock phase restorer has detected a flank so that only the period length is searched almost random.

33.	Input for the externally detectable security break, which makes it possible to use other security mechanisms.

34.	Signal for power breaks, for making it possible to deactivate at unauthorized disconnection.

35.

Control circuit for fast disconnection may be implemented if improved security is required, e. g. for computers, where there is a demand for quick disconnection to restrict the availability of e. g. data. This is essentially a function which may be provided with or without time measures after the users specification. When communication happens over a channel in which capacity and interference are no problems, the code can be extended with extra bits for complete or partially unique time/synchronising identification of the code. These bits may be randomly chosen, but must be determined and unique as for the position in the sequence, alternatively this may be the clock reference of the system. As an additional functionality in equipment being turned of and on often or is moved from place to place this additional code may be used as time markers to improve the routine when the equipment seldom or never gets more than parts of the total code sequence to recognize where in the sequence it is. How much code that is used and how often synchronising is done depends on the apparatus. Simpler apparatuses may use the first part of the code and function as described above. As more equipment is provided with improved real time clocks it may be unnecessary to transmit this time information. The disconnecting electronics learns how long the code sequence is and may use the time reference to synchronise itself against the transmitted sequence. Thus departures may be detecting with certainty even for very short signal sequences. This information is without value for the thief until he has the complete code. Additional information as described above may also be provided so that different home locations may be identified, e. g. for movable equipment, or may indicate which code sequence it should listen for. The registers for the disconnecting electronics must essentially be duplicated for each additional location, but this way functionality may be added for a few home locations. Teaching of the system will then require a certain interaction with the user. Essen tially this means that he before use indicates on how many locations he will allow the equipment to be used, and that he activates each location before the equipment is secured. This functionality gives increased flexibility in addition to have identical code transmitters in each home location. Identical code transmitters will be a more simple possibility in many cases. More registers costs larger silicon area, but the implementation is very simple. The disadvantage related to activation of the must also be taken into regard. This extension will be especially useful if the system is coupled to users rather than to home locations. For example a car may be protected against use when none of the family members are present with their personal code transmitter, as described as secondary units for transmitting code. The disconnection signal may also be used to let the equipment transmit an active message about a security breach. This may go to a form of alarm central or it may be used to broadcast that the security is broken to have an effect as an ordinary siren alarm. Each of the circuit components described above, such as memory, clock circuits registers and similar, may be of usual, available types, and are not essential in this connection other than their function in the circuit. Thus they are not described any closer here. Claims 1. System for theft securing of electronic equipment, the system comprising a transmitter (22), preferably at a position differing from the position of the electronic equipment (27), the transmitter being adapted to generate a signal containing a code adapted to be transmitted to the electronic equipment, and the equipment (27) being provided with a control device (21) adapted to receive and recognize the transmitted code and based on the received code allow for use of the equipment, c h a r a c t e r i z e d in that the generated code has a duration stretching over a long time period, preferably more than 12 hours, and that the control device (21) is adapted to discontinue the functioning of the equipment (27) at a nonappearance of the code.

36.	2 System according to claim 1, c h a r a c t e r i z e d in that the code comprises code parts generated in separate parts of the time period.

37.	3 System according to claim 1 or 2, c h a r a c t e r i z e d in that the control device is integrated in the circuits of the electronic equipment for deactivation of these, e. g. by disconnecting the power supply.

38.	4 System according to any one of the preceding claims, c h a r a c t e r i z e d in that the signal is transferred through electric conductors, e. g. the power supply net.

39.	5 System according to any one of the preceding claims, c h a r a c t e r i z e d in that the transmitter is positioned in a theft secured and/or hidden position.

40.

6 System according to any one of the preceding claims, c h a r a c t e r i z e d in that the control device comprises a first electronic memory, the memory during the first installation receiving and storing the received code, and the said recognition of the code comprising a comparison of the code with the first stored code sequence.

41.	7 System according to any one of the preceding claims comprising per se known error correction routines, e. g. by allowing 5% difference from each 10 % of the received code from the originally received code.

42.	8 System according to any one of the preceding claims, c h a r a c t e r i z e d in that it comprises transfer means for transferring the transmitted signal to the equipment to be protected.