DE102004047080A1 - Data processing system e.g. internal combustion engine control, for motor vehicle, has ROM containing operational data, where part of unencrypted data has decryption key computing algorithm that is executed in runtime of system - Google Patents

Abstract

The system has a read only memory (ROM) containing program instructions and parameters, which are referred as operational data, to be executed by a microcontroller module (1). A part of unencrypted operational data has a decrypting algorithm and an algorithm for computing a key required for decryption, which is executed in the runtime of the system. The key computing algorithm is stored in a memory integrated into the module. An independent claim is also included for a method for operating a data processing system.

Description

State of technology

The The present invention relates to a data processing system with a processor chip such as a microprocessor or microcontroller and a read-only memory, the program instructions to be executed by the processor module and Contains parameters, to which these program statements read read. If such Computer systems for controlling a machine such as the internal combustion engine of a motor vehicle are used, there is a risk that the operational safety and / or the lifetime such a machine is impaired, if the program statements and parameters, summarizing in the following to be designated as operating data, by an unauthorized party be manipulated.

Especially in the engine control units for motor vehicles is the interest of unauthorized persons to make such manipulations, very large, because they allow, for example, the available power of the internal combustion engine. The consequence of such manipulations may be that in the long term the so controlled Motor damage takes legal regulations over the Pollutant content of the exhaust gases of the engine are no longer respected, or that the vehicle reaches speeds for which its suspension is not designed is and where it is no longer safe to control. It therefore exists significant need for techniques that make it impossible for unauthorized persons the operational data of a data processing system such as a Engine control unit to manipulate, or at least manipulate so cumbersome and laborious that they are prohibitive is expensive.

So For example, it is known to be stored in a read-only memory Operating data of such a data processing system such as characteristic curves for the Motor control to an integrity check value calculate, that is a data value that deals with every change in a single Memory location of the operating data changes, and this together with the operating data in the read-only memory store. A manipulation of the operating data then leads to a high, of the bit count of the integrity check value dependent probability in addition to that a processor module calculated at a system startup Integrity check value not matches the value stored in the read-only memory, so that the processor chip is capable of manipulation to recognize and refuse to operate. However, if one Unauthorized person knows the rule according to which the integrity check value is calculated is, he is able, due to manipulated operating data also a changed one Integrity check value in to write the read-only memory, so that the manipulation is not more can be recognized.

One Another known approach is safety-relevant operating data in encrypted Form in the read only memory store and only during the Decrypting operation of the data processing system. Of the key itself is customary in unencrypted Form stored in the same memory block as the encrypted operating data. It is therefore possible for example by desoldering of the memory module containing the data, the key and the encrypted Read data. An unauthorized person can thus if he uses the encryption algorithm knows, decode the operating data, manipulate, re-encrypt and the encrypted write manipulated operating data back to the memory module, without it possible is to recognize this.

Advantages of invention

By The present invention as defined in claim 1 will be Data processing system created by simple means the unauthorized access to operating data of the data processing system considerably more difficult.

This Advantage is essentially achieved in that the data processing system according to the invention unlike conventional, an encryption the operating data using Sys temen without readable from a read-only memory key gets along. Instead, the system of the invention uses a key that only during the running time of the system is calculated. This eliminates the Necessity, the key permanently stored in a memory by an unauthorized person abusively could be read. To the operating data of a data processing system according to the invention To manipulate, the unauthorized person therefore does not need only the decryption algorithm the operating data, but also the algorithm with which the processor module of the data processing system from this key the contents of the key locations.

To make it difficult for an unauthorized person to find out this calculation algorithm, the latter is preferably stored in a memory area of the data processing system which is integrated into the processor module and therefore, if at all, can only be read by an unauthorized person with considerable technical effort. The key memory locations, on the other hand, whose number can be substantially larger than the memory area required to store the calculation algorithm, are preferably located at least partially in the memory module separate from the processor module, since the memory space there is generally less expensive.

Preferably at least make the key locations a contiguous address range the read-only memory, in particular the memory module.

If the data processing system is an engine control unit, so contains this related Address range preferably operating data, that is code and parameters, an engine control algorithm, their unnoticed manipulation it must be prevented by an unauthorized person. More generally The contents of a majority of key storage locations should have operational data of one third algorithm that works neither with the key calculation nor with the Decryption algorithm matches.

Basically it would be possible that all key storage operating data this third algorithm are. However, this would mean that, even if authorized changes be performed on this operating data, that of the key calculation algorithm calculated key changes and as a result, the decoding of the key-secured Operating data fails. To avoid this, at least one must Key space be present, its contents are not the operating data of the third Algorithm belongs, so that after a change this operating data, the content of this storage space is adjusted that can be the key calculation algorithm continue the correct key supplies.

Preferably is at least part of the stored at the key locations Operating data of the third algorithm is encrypted. The calculation of the key finds then on the basis of the still encrypted Contents of these memory locations take place, while for execution of the third algorithm which has been decrypted in the meantime Operating data can be used.

The Data processing system should expediently for recording the from the encrypted Operating data obtained decrypted Operating data a volatile Have read-write memory, during the operation of the data processing system instead of the read-only memory is accessed. Because on this fleeting Store the decrypted Operating data only during the duration of the data processing system are available, Unauthorized access to them is also difficult.

object The invention is also an operating method for a data processing system of described above, in which first the key calculation algorithm is performed, around the key to get, and this key in a fleeting Memory is stored, then the decryption algorithm is executed, a needed one Part of the operational data to decrypt, and before, with it is started, with the decrypted Operating data, which then deletes unneeded keys, so he for an unauthorized person is no longer accessible.

key calculation and decryption can each run once at the start of the data processing system, around all for the Operation of the system needed To decrypt operating data; but it can also be provided that only a part of the Operating data decrypted will, and that while the operation of the system whenever operating data not yet decrypted needed be, the calculation of the key is repeated.

Further Features and advantages of the invention will become apparent from the description of exemplary embodiments with reference to the attached Characters.

characters

It demonstrate:

1 a block diagram of a data processing system according to the invention; and

2 a flowchart of a working method of the data processing system 1 ,

description the embodiments

This in 1 The data processing system shown comprises a microcontroller module 1 in which a processor unit 2 , a read-only memory area 3 and a random access memory area 4 integrated on a common semiconductor substrate. processor unit 2 and storage areas 3 . 4 communicate via an internal bus 5 of the building block 1 comprising data and address lines.

The microcontroller module 1 also communicates via an external bus 6 with a read-only memory module 7 , for example, a flash IC, and a volatile memory device with optional em access or RAM 8th ,

The data lines of the internal bus 5 and the external bus 6 are inside the microcontroller chip 1 galvanically isolated from each other, leaving data over the internal bus 5 between the processor unit 2 and the internal memory areas 3 . 4 be exchanged, outside the microcontroller module can not be tapped. To the contents of the internal memory areas 3 . 4 Therefore, an unauthorized person is therefore forced to open the housing of the microcontroller module and, if it survives the opening, operate it in order to pick up the signals on the internal bus lines and to deduce the memory contents therefrom.

The address lines of the buses 5 . 6 can be galvanically connected, at least in principle, if both buses have the same timing and the internal memory areas 3 . 4 and the external memory devices 7 . 8th use a common address space.

The read-only memory module 7 contains an unencrypted memory area 9 in which at least part of one of the processor unit 2 stored operating program is a sensitive area 10 whose manipulation by unauthorized persons is to be prevented, an offset area 11 and possibly an area 12 which contains more data. The sensitive area 10 contains in particular constants to which the processor unit 2 accessing the operating program. For example, if the data processing system is an engine control unit, in the sensitive area 10 be used for the engine control characteristics used to be set by the control unit on the engine relationships between different operating variables such as an air-fuel ratio to be adjusted, valve opening and closing angle, ignition angle or the like as a function of engine load and / or speed etc .. specify. The sensitive area 10 but can also contain parts of the operating program.

The content of the sensitive area 10 is in the read-only memory device 7 stored in encrypted form and therefore can not be used as an operating program or by the operating program without prior decryption.

An algorithm for decrypting the content of the sensitive area 10 is part of the operating program; he is in the unencrypted storage area 9 stored.

The internal read-only memory area 3 of the microcontroller module 1 contains an algorithm for calculating a key required by the decryption algorithm from the content of the sensitive area 10 and one in the offset area 11 stored offset.

The key calculation algorithm is largely consistent with conventional integrity checking algorithms for detecting manipulations in a data set. Such integrity checking algorithms each comprise the calculation of a function of a data set to be checked and then the comparison of the function value calculated on a version of the data record to be checked with the known value that the function has for the original data record. In the simplest case, the function to be calculated may be the parity or a checksum of the record to be checked. In the other extreme case, the function could also be a data compression function, ie a function whose result comprises fewer bits than the data record to be checked but contains all its information. Such a function would provide the certainty that any manipulation will result in a change in the outcome and be recognized. In practice, one will usually use a function in which the bit number of the result corresponds to the single or double width of the data bus. With a bit count of 16, the probability that a manipulation does not lead to a change in the functional result is negligible, in the best case 2 ^-16 .

The inventive key calculation method is limited to the calculation of the function value, wherein the data of the sensitive area 10 be used as an argument of the function; However, a comparison of the function value thus obtained with an expected value does not take place - in contrast to a conventional integrity check.

2 shows on the basis of a schematic flow chart the flow of processing in the data processing system of 1 which follows at the start of the system.

The first part of the processing with steps S1 and S2 is the key calculation. The program instructions required for their execution are read by the processor unit 2 from the internal memory area 3 , In step S1, it computes the integrity checking function explained above with the content of the sensitive area 10 as an argument. For the function result, it adds the content of the offset range in step S2 11 added. At the offset area 11 it is a memory address whose contents - in contrast to the sensitive area 10 - is used exclusively for the key calculation. The key thus obtained is placed by the processor unit 2 in the internal random memory area 4 of the building block 1 from (S3).

Subsequently, the processor unit leads 2 in step S4, the memory area 9 stored instructions of the decryption algorithm using the in memory area 4 saved key to the contents of the sensitive area 10 to decrypt and into the RAM 8th to write. If this is done, the key is in the memory area in step S5 4 deleted, and the processor unit 2 begins to execute in step S6 another algorithm that corresponds to the eigentli Chen task of the data processing system such as the control of an internal combustion engine. This algorithm uses the in the RAM 8th written decrypted data as parameters or possibly even as program instructions. If the key calculated in step S2 has been correct, then those are also in the memory 8th written decrypted data correctly, and the system can perform its task correctly. However, if the content of the sensitive area 10 has been manipulated by an unauthorized person, then the key obtained in step S2 is also wrong, and the decryption of the data of the sensitive area 10 The wrong key leads to meaningless results. An attempt to operate the system on the basis of these results therefore leads to a crash (step S7). The operation of the system is thus effectively blocked in the event of a manipulation, without the need to even compare the key calculated in step S2 with an expected key. Therefore, such an expected key does not need in any way in the read only memory device 7 so that an unauthorized person also does not have the opportunity to find him and to be taken into account in his manipulation, in whatever way. Thus, a very high degree of manipulation security is achieved in a simple manner.

A change in the data of the sensitive area 10 by an authorized person holding the correct key and in the memory area 3 is inaccessible stored key calculation algorithm, but is completely unproblematic. The authorized person can change any data of the sensitive area 10 to calculate the new value of the Integrity Checker for this changed data and into the offset range 11 Enter the numeric value that adds to the old key resulting to the result of the integrity check function resulting from the changed data.

Claims (10)

Data processing system with a processor module ( 1 ) and a read-only memory ( 3 . 7 ) generated by the processor module ( 1 ) program instructions and parameters to which these program instructions access, collectively referred to as operating data, a portion of said operating data being stored in encrypted form and an unencrypted portion of said operating data comprising a first algorithm for decrypting the encrypted portion, characterized in that unencrypted part further comprises a second algorithm for calculating a key required for decryption from the contents of a plurality of memory locations of the read-only memory ( 3 . 7 ), as key storage locations ( 10 . 11 ). Data processing system according to claim 1, characterized in that the read-only memory at least one of the processor module ( 1 ) separate memory module ( 7 ) and one in the processor chip ( 1 ) integrated memory area ( 3 ) and that the second algorithm in the memory area ( 3 ) and the key storage locations ( 10 ) at least partially in the memory device ( 7 ) are located. Data processing system according to claim 1 or 2, characterized in that the key memory locations ( 10 . 11 ) at least one contiguous address range ( 10 ) of the read-only memory ( 3 . 7 ) form. Data processing system according to one of the preceding claims, characterized in that the contents of a majority ( 10 ) of the key storage locations are operational data of a third algorithm. Data processing system according to claim 4, characterized characterized in that the contents of all keystores until to one (11) operating data of the third algorithm. Data processing system according to claim 4 or 5, characterized in that at least a portion of the stored at the key memory locations Operating data of the third algorithm is encrypted. Data processing system according to one of the preceding claims, characterized by a volatile random access memory ( 8th ) for receiving the decrypted operating data obtained from the encrypted operating data. Data processing system according to one of the preceding Claims, characterized in that it is an engine control unit Data processing system according to claim 8, characterized in that the key memory locations ( 10 ) contain required characteristic curves for controlling a connected motor. Operating procedure for data processing A system according to any one of the preceding claims, comprising the steps of: a) executing the second algorithm to obtain the key (S1, S2) and storing the key in a volatile memory (S3); b) performing the second algorithm to decrypt a required portion of the operating data (S4); c) deleting the key (S5); and d) working with the operating data (S6).