Method for protecting devices, specially car radios, against theft

IS 2 189 181 T3

DESCRIPTION

Procedure for obtaining anti-theft protection for devices, especially for car radios.

The invention relates to a method for obtaining an anti-theft protection for devices, especially for car radios, where a distinctive identifying the device must be inserted to activate the device directly on the device.

State of the art

A process according to the preamble of claim 1 is known from document US-A-4 759 062.

It is known to provide car radios with an anti-theft protection code. To this end, a secret code is stored in a memory assigned to the car radio. This can be done, for example, on an internal or external EEPROM (electrical evaluated read-only memory). To start up or to resume operation after a power supply interruption for a car radio, the code must be entered directly into 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 entered and in the event of a match, the car radio is free for unlimited use.

In this case, it is a disadvantage that the secret code stored in the car radio can be read relatively easily. By knowing the code through unauthorized reading, the radio can also be activated by unauthorized users.

Advantages of the invention

On the other hand, the method according to the invention with the characteristics mentioned in claim 1 offers the advantage that unauthorized use of an anti-theft device is not possible. Since the coding is determined by means of a non-reversible coding procedure from a control information assigned to the device, the anti-theft protection code itself is not deposited in the device. In this way, it is prevented that this coding can be read in an unauthorized way and can be misused for the unauthorized start-up of the device. As non-reversible coding procedures, for example, asymmetric procedures are used, especially the so-called RSA procedure (Rivest-Shamir-Adelmann procedure). These procedures offer the advantage of a very high cryptographic quality, that is, a decoding of an encoded information through an asymmetric procedure is only possible through systematic testing with an extremely high cost of time and calculation, which is not available. an economic relationship with achievable profit.

In a preferred configuration of the invention, it is envisaged that in a processor or in a memory element of the apparatus associated with the processor, a public key of the encryption procedure and the starting information of the encryption (control information) are stored, especially a serial number of the device to be protected. With the knowledge of this information, it is not possible for an unauthorized user to determine the coding for an unlimited use of the device to be protected. Only through the external input of the coding through the authorized user, for example manually or by means of a code card, is it possible to calculate the control information, the comparison of which with the memorized control information makes possible, in case of identity, the release of the device.

In another preferred configuration of the invention, it was envisaged that, in addition to the control information, a control algorithm is deposited in the apparatus to be protected. In this way, it is possible with advantage to reduce the expense for coding and maintenance of a non-reversible coding procedure to a minimum. Without the relatively expensive use of a complete asymmetric procedure, a non-reversible coding can also be performed in this way, in effect depositing a control algorithm for a coding, but not the coding formation algorithm. The control algorithm and the control information, which are legible, also allow only at a high cost to obtain the training algorithm for the encoding and, therefore, the encoding itself. Other advantageous embodiments of the invention appear from the other features mentioned in the claims.

Drawings

In the following, the invention is explained in detail in exemplary embodiments with the aid of the corresponding drawings. In this case:

Figure 1 shows schematically a coding of a device.

Figure 2 shows in a schematic way an operation of a coded device.

Figure 3 schematically shows a coding of an apparatus according to a second embodiment example and

Figures 4 and 5 show schematically an operation of a coded apparatus according to the second embodiment.

Description of the realization examples

With the help of the realization examples explained below, we start from the creation and use of an anti-theft protection code for car radios. However, in principle, this procedure can be applied to all appliances worthy of protection.

Figure 1 shows the creation of the coding according to the invention. In this case, an asymmetric encryption algorithm 10 is fed with a control information 12, which is processed with a secret key 14, so that an encryption 16 is formed. As control information 12, for example, the number standard of the device to be protected, therefore, for example, of the car radio. Starting from this serial number or from a part of the serial number, for example from a discretionary section of

ES 2 189 181 T3 individual digits of the serial number, code 16 is formed in a secure environment during the manufacture of the car radio by means of the secret key 14. Code 16 is added to the car radio during the first delivery or during a desired transmission. This can be done, for example, in the form of a written communication via encryption or in the form of a code card, which presents the encryption 16 in memorized form.

The car radio itself contains a processor unit, inside which the control information 12 was stored as unaltered information and a public key 18 of the asymmetric coding procedure 10 used.

The car radio 20 indicated in figure 2 does not contain, in addition to the public key 18 and the control information 12, the coding 16, which is necessary to start up or to restart the car radio 20. When starting up or resuming the authorized operation of the car radio 20, the authorized user enters the code 16 in the car radio processor 20. This can be done, for example, by means of a key entry of the coding 16 communicated in writing or by means of the introduction of the code card. The asymmetric coding procedure 10 determines from the entered coding 16 and the public key 18 a calculated control information 12 '. The control information 12 'is compared with the control information 12 stored invariably in a comparator 22. If the comparison 22 results in an identity between the control information 12 and the calculated control information 12 ', the car radio 20 is released for unlimited use 24.

It is clear that in the case of a theft of the car radio 20, the public key 18 accessible to anyone of the asymmetric coding procedure 10 used and the control information also accessible to anyone, for example the serial number, was available. but the coding 16 was not available in any way for the determination of the calculated control information 12 '. Nor can the coding 16 be determined from the public key 18 of the asymmetric coding procedure 10 used.

It was absolutely clear that without knowledge of the coding 16 the start-up or the resumption of operation of the car radio 20 was excluded.

Since the expense for the non-reversible asymmetric coding procedure, described with the help of Figures 1 and 2, for certain groups of devices to be protected was not in any relation to the economic utility, it is described with the aid of Figures 3 and 4 a simplified non-reversible coding procedure.

In a manner similar to FIG. 1, the control information 12, for example the serial number of the car radio, is fed to a 10 'encoding procedure. Through an algorithm 26, the coding is determined from the control information. Coding 16 is attached back to the car radio either in writing or in the form of a code card.

As shown in figure 4, the start-up and the resumption of operation of the car radio is carried out through the input of coding 16 on the car radio 20. Through the coding procedure 10 'the coding is promoted 16 with a control algorithm 28 and with the control information 12. The control algorithm 28 checks the encoding 16 to determine if it can be put in connection with the control information 12. If it is verified through the control algorithm 28 that the coding 16 belongs to the car radio 20 containing the control information 12, the release is carried out for an unlimited use 24 of the car radio 20.

The non-reversible coding procedure, explained with the aid of Figures 3 and 4, is also characterized in that the car radio 20 itself does not contain the coding 16 nor the coding training algorithm 26. Only the control information 12 and the control algorithm 28 are contained, which does not allow, through unauthorized reading, unlimited access to the encoding 16. Only through costly analysis procedures for the control algorithm 28 can the training algorithm 26 be deduced for the code word 16. In this way, an anti-theft protection for car radios 20 or 20 is also achieved with this simplified non-reversible coding procedure. good for other devices to protect.

According to the need for protection of the devices to be protected, it is possible to select between the more expensive asymmetric coding procedure according to Figures 1 and 2 or the simpler pseudoasymmetric coding procedure according to Figures 3 and 4.

Figure 5 represents the start-up of a coding apparatus according to the second embodiment, in which the coding 16 and the control algorithm 28 are fed to the coding procedure 10 ', which generates from this the control information 12 '. The control algorithm 28 is in this case together with the control information 12 on the car radio 20. In the comparator 22, the control information 12 'in the car radio is compared and in the case of free identity the unlimited use 24 of the car radio.