Title of Invention	A METHOD FOR ATTAINING ANTI-THEFT PROTECTION FOR DEVICES,IN PARTICULAR FOR CAR RADIOS
Abstract	The invention relates to a method for attaining anti-theft protection for devices, in particular for car radios, it being necessary to input an identifier (code), identifying the device, directly at the device in order to activate the device. It is provided that the code is determined by means of an irreversible encryption method from a check information item assigned to the device. FIGURE 1.

Full Text

ROBERT BOSCH GMBH, 70442 Stuttgart Method for attaining anti-theft protection for devices, in particular for car radios The invention relates to a method for attaining anti-theft protection for devices, in particular for car radios, it being necessary to input an identifier, identifying the device, directly at the device in order to activate the device. Prior art It is known to provide car radios with an anti-theft protection code. For this purpose, a secret code is stored in a memory assigned to the car radio. This can be done for e&le in an internal or an external EEPROM (Electrical'; evaluated read only memory) . For the purpose of initial starting or restarting after an interruption of the voltage supply for the car radio, the code must be input directly at the car radio. This can be done either manually via input keys or via an external code card. A processor unit integrated in the car radio compares the stored secret code with the code that has been input, and enables the car radio for unrestricted use in the event of correspondence. The disadvantage in this case is the fact that the secret code stored in the car radio can be read out in a relatively simple manner. Knowledge of the cpde by way of unauthorized read-out means that the car rad^o can also be activated by unauthorized users. Advantages of the invention In contrast, the method according to the invention having the features mentioned in Claim 1 affords the advantage that unauthorized use of a device having anti-th^ft protection is not possible. Since the code is determined by means of an irreversible encryption method from a check information item assigned to the device, the anti-theft protection code itself is not stored in the device. This prevents the said code from being able to be read out in an unauthorized manner and misused for unauthorized starting of the device. Asymmetrical methods for example, in particular the so-called RSA method (Rivest-Shamir-Adelman method), are used as irreversible encryption methods. These afford the advantage of a very high cryptographic quality, that is to say an information item encrypted by an asymmetrical method can be decrypted only by systematic trial and error taking an extremely long time and requiring an extremely high computation effort, which is not economically viable with respect to the benefit that can be obtained. A preferred refinement of the invention provides for a public key of the encryption method and the encryption source information (check information item), in particular a serial number of the device to be protected, to be stored in a processor or a memory element, assigned to the processor, of the device. With a knowledge of these information items, an unauthorized user cannot determine the code for unrestricted use of the device to be protected. Calculation of the check informa-tion item, ' comparison of which with the stored check information item permits the device to be enabled in the event of identity, becomes possible only by external input of the code by the authorized user, for example manually or by means of a code card. A further preferred refinement of the invention provides for not only the check information item but also a check algorithm to be stored in the device to be protected. This advantageously enables the encryption outlay to be minimized whilst retaining an irreversible encryption method. Without the relatively complex upe of a complete asymmetrical method, it is thus also possible for irreversible encryption to be effected by storing a check algorithm for a code, but not the formation algorithm of the code. The check algorithm and the check information item, which can be read out, likewise permit the formation algorithm for the code and thus the code itself to be obtained only with an increased effort. Further advantageous refinements of the invention emerge from the remaining features mentioned in the subclaims. Drawings The invention is explained in more detail below using exemplary embodiments with reference to the associated drawings, in which: Figure 1 schematically shows encryption of a device; Figure 2 schematically shows starting of an encrypted device; Figure 3 schematically shows encryption of a device according to a second exemplary embodiment; and Figure 4 schematically shows starting of a device that has been encrypted according to the second exemplary embodiment. Description of the exemplary embodiments The exemplary embodiments explained below are based on the creation and use of an anti-theft protection code for car radios. In principle, however, this method can be applied to all devices worthy of protection. Figure 1 shows the creation of the code according to the invention. In this case, an asymmetrical encryption!algorithm 10 is supplied with a check informa-tion item 12, which:is processed with a secret key 14 to form a code 16. The serial number of the device to be prQtected, that is to say of the car radio, for example, may be used as the check information item 1?, for example. From this serial number or part of the perial.. number, for example any desired selection of individual digits of the serial number, the code 16 is forrped by means of the secret key 14 in a secure environment during manufacture of the car radio. The code 16 is enclosed with the car radio the first time the latter is delivered or when it is intentionally passed on. This can be done for example in the form of a written communication regarding the code or in the form of a code card having the code 16 in stored form. The car radio itself contains a processor unit within which are stored the check information item 12 as invariable information and a public key 18 of the asymmetrical encryption method 10 used. The car radio 20 indicated in Figure 2, therefore, contains the public key 18 and the check information item 12 but not the code 16 which is necessary to start or restart the car radio 20. For authorized starting or restarting of the car radio 20, the authorized user inputs the code 16 into the processor of the car radio 20. This can be done for example by means of a key input of the code 16 communicated in writing, or by means of the inputting of a code card. The asymmetrical encryption method 10 determines a calculated check information item 12' from the code 16 that has been input and the public key 18. The check information item 12' is compared with the invariably stored check information item 12 in a comparator 22. If the comparison 22 yields identity between the check information item 12 and the calculated check information item 12', the car radio 20 is enabled for unrestricted use 24. It becomes clear that if the car radio 20 is stolen, although the public key 18 (accessible to anybody in any case) of the asymmetrical encryption method 10 used and the check information item (also accessible to anybody), for example the serial number, are available, the code 16 for determining the calculated check information item 12' is not available under any circumgtances. Moreover, the code 16 cannot be determined from the public key 18 of the asymmetrical encryption method 10 used. It becomes quite clear that without a knowledge of the code 16, starting or restarting of the car radio 20 is precluded. Since the outlay for the irreversible asymmetri- cal encryption method described witn rererence co figures 1 and 2 is not viable with respect to the economic benefit for certain groups of devices to be protected, a simplified irreversible encryption method is described with reference to Figures 3 and 4. In a manner analogous to Figure 1, the check information item 12, for example the serial number of the car radio, is fed to an encryption method 10'. The code 16 is determined from the check information item by means of a formation algorithm 26. The code 16 is again enclosed with the car radio either in writing or in the form of a code card. The car radio 20 is started or restarted, as shown by Figure 4, by the code 16 being input at the car radio 20. The code 16 is exposed to a check algorithm 28 and the check information item 12 by the encryption method 10'. The check algorithm 28 checks the code 16 to see whether the latter can be brought into association with the check information item 12. If the check algorithm 28 establishes that the code 16 belongs to the car radio 20 containing the check information 12, enabling for unrestricted use 24 of the car radio 20 is effected. The irreversible encryption method explained with reference to Figures 3 and 4 is likewise distinguished by the fact that the car radio 20 itself contains neither the code 16 nor the formation algorithm 26 of the code 16. All that are contained are the check information item 12 and the check algorithm 28, which does not permit direct access to the code 16 even as a result of unauthorized read-out. The formation algorithm 26 for the code 16 can be inferred only from complex analysis methods for the check algorithm 28. Consequently, anti-theft protection for car radios 20 or for other devices worthy of protection is also achieved by this simplified irreversible encryption method. It is possible to select between the more complex asymmetrical encryption method according to Figures 1 and 2 pr the simpler pseudo-asymmetrical encryption method according to Figures 3 and 4 depending on the protection requirement of the devices to be safeguarded. 1. Metnoa tor attaining anti-theft protection for devices, in particular for car radios, it being necessary to input an identifier (code), identifying the device, directly at the device in order to activate the device, characterized in that the code is determined by means of an irreversible encryption method from a check information item assigned to the device. 2 . Method according to Claim 1, characterized in that an asymmetrical encryption method is used for the encryption. 3. Method according to Claim 2, characterized in that the RSA method (Rivest-Shamir-Adelman method) is used. 4. Method according to one of the preceding claims, characterized in that the code can be determined by means of a secret key at a secure location for each device. 5. Method according to one of the preceding claims, characterized in that a public key for the code and a check information item are stored in the device. 6. Method according to Claim 1 or 2, characterized in that a check algorithm for the code and the check information;item ar6 stored in the device. ' i ■ ■ ' 7: Method according to one of the preceding claims, characterized in that a serial number or part of the serial number of the device is used as the check information item.

Documents:

825-mas-1998- abstract.pdf

825-mas-1998- claims duplicate.pdf

825-mas-1998- claims original.pdf

825-mas-1998- correspondence others.pdf

825-mas-1998- correspondence po.pdf

825-mas-1998- description complete duplicate.pdf

825-mas-1998- description complete original.pdf

825-mas-1998- description provisional.pdf

825-mas-1998- drawings.pdf

825-mas-1998- form 1.pdf

825-mas-1998- form 26.pdf

825-mas-1998- form 3.pdf

825-mas-1998- form 4.pdf

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