Abstract:
It should not be possible for control units for motor vehicles to be exchanged between individual motor vehicles by unauthorized persons. For a motor vehicle it should, therefore, be rendered possible for individual functionalities of a control unit to be unblocked only for a specific motor vehicle. For this purpose, a first cryptographic key and a second cryptographic key are stored in a control unit. A cryptographic device is designed to encrypt a first message initially by one of the cryptographic keys, subsequently to encrypt a result of the encryption by the other cryptographic key and, finally, to provide a result of the second encryption as third cryptographic key for an encryption and/or decryption of a further message. A method configures a control unit in a motor vehicle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to International Application No. PCT/EP2012/000362 filed on Jan. 27, 2012 and German Application No. 10 2011 014 688.1 filed on Mar. 22, 2011, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The invention relates to a control unit for a motor vehicle, a cryptographic device for encrypting and/or decrypting a message being provided in the control unit. The a method for configuring the control unit for use in the motor vehicle. 
     In a motor vehicle, functionalities such as, e.g., an engine controller, navigation assistance or telephony are provided by individual control units. It should not be possible for the control units to be exchanged between individual motor vehicles by unauthorized persons. Thus, on the one hand, it should not be possible for any stolen control units to be used in other motor vehicles. On the other hand, the installation of a used control unit in a motor vehicle by an unskilled person can endanger the safety of a user of the motor vehicle. 
     From DE 10 2006 040 228 A1, an identification system for control units in a motor vehicle is known by which it is possible to check whether a control unit has been installed in the motor vehicle by an authorized person. For this purpose, an identification code of the motor vehicle is encrypted by a (private) cryptographic key of an asymmetric encryption method and the encrypted identification code is stored in the control unit. The encrypted identification code can be read out again later from the control unit by a test unit, decrypted on the basis of a complementary cryptographic key (public key) and then checked. 
     From WO 2005/116834 A1, a method for authenticating a control unit in a vehicle is known. According to this, the control unit sends an authentication request to an authentication device of the vehicle before it provides a functionality. The authentication request is encrypted by the authentication device by a cryptographic key and subsequently sent back to the control unit. In the control unit, it is checked by the encryption result sent back whether the control unit is authenticated for the vehicle. 
     In EP 1 139 064 A1, a navigation system is described in which it is checked whether a user of data such as, for example, road map data, is authorized to use these data. To unblock the usage rights for a file, it is provided that the user initially inputs a first and second encrypted code into the navigation system. By an equipment identifier of the navigation system and the first encrypted code, a key is first calculated. The files are also encrypted by the key so that the files can be read by the key. 
     US 2004/0003231 A1 shows a control unit for a motor vehicle. The control unit authenticates itself to the motor vehicle by a challenge-response method and the motor vehicle authenticates itself to the control unit by a challenge-response method. In this method, e.g. a private key and a certificate with the associated public key is allocated to the control unit. The vehicle checks the certificate and sends a challenge to the control unit. The control unit encrypts the challenge using the private key and sends it back as a response. The vehicle can decrypt and check the response using the public key. The same method can also be performed by the control unit. The control unit is tied to the vehicle due to the mutual authentication. 
     DE 10 2009 025 585 A1 shows a method for unblocking a vehicle function in a control unit on the basis of a function activation code. The unblocking code is formed from the chassis number and the serial number of the control unit and signed with a private key. The control unit checks the signature, the chassis number and the serial number and activates the vehicle function correspondingly. 
     In DE 10 2008 008 108 A1, a function is unblocked by an unblocking code, the unblocking code being encrypted by a key allocated to the vehicle and decrypted by a mobile telephone allocated to a user. The unblocking code is thus tied to the vehicle and to the user. 
     WO 03/019 337 A2 shows a method in which software for a vehicle control unit is executed only when there is an unblocking code certificate and a signature has been checked by a stored public key. In addition, the unblocking code contains the chassis number and the control unit number in order to restrict the utilization of the software to the combination of chassis number and control unit number. 
     SUMMARY 
     One potential object is to provide a possibility so that a particular control unit or a particular functionality of the latter can only be used in a particular motor vehicle. 
     The inventors propose a control unit of a motor vehicle, in which control unit a first cryptographic key and a second cryptographic key are stored. Additionally, a cryptographic device is provided which is designed to encrypt a first message initially by one of the cryptographic keys, subsequently to encrypt a result of the encryption by the other cryptographic key and, finally, to provide a result of the second encryption as third cryptographic key for an encryption and/or decryption of a further message. 
     Cryptographic keys are already known as such from digital cryptographic methods. In conjunction with the inventors&#39; proposals, the keys are preferably in each case those for a symmetric encryption method. The input for an encryption or decryption algorithm is called a message. It can be formed of a character sequence (letters or numbers), an individual character or generally of a bit sequence of arbitrary predetermined length. 
     An encryption of the further message by the third key always produces an encryption result which depends both on the first and on the second key. As a consequence, it is possible to enforce in the control unit, by specifying a corresponding first and a corresponding second key, that both an identification feature of the control unit itself and also of the motor vehicle in which the control unit may only be operated, is impressed on the encrypted further message. By the third cryptographic key, the cryptographic unit is then able to encrypt the further message in dependence on both the first and the second predetermined key by only a single encryption process. In comparison with specifying only a single key, there is thus no resultant loss with respect to the expenditure of time and calculation. This correspondingly also applies to a decryption. 
     The first cryptographic key is a key generated individually for the control unit. In the case of an exchange of an authenticated control unit by another, not authenticated control unit, this newly inserted unit is then not capable of deciphering encrypted messages intended for the authenticated unit in a motor vehicle. 
     The second cryptographic key is a motor-vehicle-specific key. Correspondingly, the motor vehicle has at least one of the proposed control units in which the stored second cryptographic key is a key generated individually for this motor vehicle. The respective control unit can then only process the messages encrypted for this motor vehicle, or only generate such messages, respectively. A control unit stolen from the motor vehicle can thus advantageously not be used in any other motor vehicle. 
     In order to be able to specify the second cryptographic key during the installation of the control unit in a particular motor vehicle in a simple manner, the control unit preferably has a device for receiving a cryptographic key from outside the control unit and for specifying the received key as the second cryptographic key. This results in the advantage that a used control unit can also be used again in a motor vehicle in that the second key is correspondingly adapted in the control unit. By new double encryption of the first message, the control unit is then able to newly generate the third key for encrypting and decrypting the further message, respectively. 
     The first message is preferably stored in the control unit. It is then sufficient to store the new vehicle-specific key and the control unit is able independently to generate the further (third) key. 
     By the method proposed by the inventors, at least one proposed control unit can be configured correspondingly for use in a motor vehicle. According to the method, a cryptographic key is generated for each control unit, a different individual key being generated for each control unit. A further cryptographic key is generated which is allocated to the motor vehicle as motor-vehicle-specific key. In each control unit, the respective individual key is stored as first key and the motor-vehicle-specific key is stored as second key. By the method, it is advantageously ensured that each control unit has a unique combination of a unit-associated key and a vehicle-specific key. 
     According to a further aspect of the proposal, the control unit has an unlocking device for unblocking a functionality of the control unit in dependence on an unblocking code which can be predetermined from outside the control unit. The unblocking device is designed to encrypt a message, standing for the functionality to be unlocked, by the cryptographic device by the third cryptographic key, to compare a result of the encryption with the unblocking code and to unlock the functionality in dependence on the comparison. The unlocking code is preferably formed in the same manner so that an encryption result identical with the unblocking code is produced when the control unit is used in the correct vehicle. This development of the control unit has the advantage that an unblocking code can be used which provides for unblocking for precisely one particular control unit in precisely one particular motor vehicle. 
     Correspondingly, the proposed method is advantageously developed if for each control unit, a copy of the individual key and a copy of the motor-vehicle-specific key are stored outside the control units. An unblocking code is then generated for unlocking a functionality of one of the control units on the basis of the corresponding individual key stored outside the control unit and of the motor-vehicle-specific key stored outside the control unit and is conveyed to the control unit to be unblocked. An unblocking code needed can be generated at any time for a particular control unit in a particular motor vehicle by storing the unit-associated keys and the motor-vehicle-specific key. 
     The keys are stored preferably in a central database outside the vehicle. The first message needed for generating the third key is also stored as a copy preferably likewise outside the control units. 
     If the first and the second key are those for an asymmetric encryption method, a key, complementary thereto, is stored in each case instead of the copy of the key. 
     The control unit can be developed further by a compressing device for generating a shortened encrypted message from a message encrypted by the encryptographic device. This results in the advantage that very short character sequences can be generated which, nevertheless, are suitable for unlocking the control unit for use in a particular motor vehicle. The shortened encrypted message in this arrangement can be generated preferably by a CRC method or a hash method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawing of which: 
       The FIGURE shows a diagrammatic representation of a proposed control unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawing, wherein like reference numerals refer to like elements throughout. 
     The FIGURE shows a control unit  10  which is installed in a passenger vehicle (not shown in greater detail). In conjunction with the example forming the basis of the FIGURE, it is assumed that the control unit is a navigation unit of the passenger vehicle. In general, however, it can be a control unit by which any other functionality is provided instead of the navigation assistance. 
     A route calculation necessary for the navigation assistance and a generation of driving instructions via a digital display (not shown) of the navigation unit is controlled by a control device  12 . The control device  12  is coupled to an encryption device  14  of the control unit  10 . An output of the encryption device  14  can be transmitted to a compressing device  16 . An output value  18  of the compressing device  16  can be transmitted to the control device  12 . 
     The control device  12 , the encryption device  14  and the compressing device  16  can be in each case a circuit arrangement of the control unit  10  or a program which is executed by a processor of the control unit  10 . 
     The control device  12  provides the “navigation assistance” functionality only if it has previously been detected that the passenger vehicle is the vehicle for which this functionality of the control unit  10  has also been authenticated. 
     For this unblocking of the control unit  10 , the control device  12  has an unblocking component  20 . Via a communication bus (not shown) of the passenger vehicle (a diagnostic bus in this case), an unblocking code  22  has been transmitted to the control unit  10 , for example during an installation of the control unit  10  in the motor vehicle. Within the control unit  10 , the unblocking code  22  has been transmitted to the unblocking component  20 . The unblocking code  22  contains, apart from other data, a vehicle identification or vehicle component reference number VCRN. In the example, it may be a 4-byte-long code by which it is specified which quite particular control unit (identified by its serial number) is authenticated for the passenger vehicle (identified by its chassis number) in conjunction with the “navigation assistance” functionality. 
     For example, it can also be provided that the control unit  10  is not unblocked during the installation, but only later by a user of the motor vehicle himself. For this purpose, it can be provided that the unblocking code is transmitted via an Internet connection from a database to the motor vehicle and is conveyed to the control unit  10 . Thus, the user can also be enabled, e.g., to unblock further functionalities of his control unit retrospectively. 
     For checking the authentication of the control unit  10 , the unblocking component  20  sends a character sequence  24 , which stands for the “navigation assistance” functionality, to the encryption device  14 . The message can include, for example, a number or a text. The character sequence  24  is stored as a constant data item in the unblocking device  20 . 
     The character sequence  24  is encrypted by the encryption device  14 . The encryption result is a 16-byte-long digital value in the example shown. This value is transmitted by the encryption device  14  to the compressing device  16 . The compressing device  16  forms from the 16-byte-long value the 4-byte-long output value  18  which is transmitted to the unblocking component  20  as a local VCRN, i.e. a VCRN which has been generated within the control unit  10 . In the FIGURE, the local VCRN is correspondingly designated as VCRN′. 
     The unblocking device  20  compares the VCRN contained in the unblocking code  22  and the local VCRN (VCRN′). If the two values are identical, the control device  14  is activated, i.e. the control unit  10  is then unblocked. Otherwise, the control device  14  is not activated so that the control unit  10  does not provide the “navigation assistance” functionality. 
     In the text which follows, the encryption of the character sequence  24  and the subsequent compression is explained again in greater detail. 
     By encrypting the character sequence  24 , the encryption device has generated an encryption result which, with the given character sequence  24 , is unique for the combination of the control unit  10  to be unblocked and the passenger vehicle in which the control unit  10  is installed. For this purpose, a control-unit-associated key  26  is stored in a memory  28  in the encryption device  14  and a vehicle-associated key  30  is stored in a memory  32  in the encryption device  14 . 
     The two keys are cryptographic keys for a symmetric encryption method. Key  26  has been generated individually for the control unit  10  during the production of the control unit  10  and stored in memory  28 . Other control units of the same series but having a different serial number have different keys in their corresponding memories. Key  30  has been generated individually for the passenger vehicle in the sense that the passenger vehicle has a unique chassis number and key  30  has been generated for this chassis number. 
     For the encryption of the character sequence  24 , a third, combined key  34  having a length of 16 byte in this case is used by the encryption device  14 . The key  34  has been generated by the encryption device  14  after a key  30  has been stored in memory  32 . For this purpose, a character sequence  38  is stored in a configuration file  36  which is stored in the encryption device  14 . The character sequence  38  can be, for example, a value or of a text. The character sequence  38  has been encrypted with the key  26  by a symmetric encryption method and the result of this encryption has been encrypted with the key  30 . The encryption method is in the example a method according to the Advanced Encryption Standard (AES). Key  34  is provided by the encryption device  14  for an encryption of messages such as the character sequence  24  by a further encryption (in this case also according to the AES) in an encryption component  40 . 
     The key  34  being formed from the control-unit-associated key  26  and the vehicle-associated key  30 , an encryption with the encryption component  40  always produces an encryption result which is marked both by the identity of the control unit  10  and by the identity of the passenger vehicle. 
     The compressing device  16  compresses the encryption result of the encryption device  40  by a CRC (Cyclic redundancy check) process. 
     The VCRN contained in the unblocking code  22  has been formed in the same manner from a copy of the character sequence  24  as the VCRN′ from the character sequence  24 . For generating the unblocking code  22 , a copy of the keys  26  and  30  has respectively been read out of a database by the serial number of the control unit  10  and the chassis number of the passenger vehicle. The database is operated by the manufacturer of the passenger vehicle. The character sequence  38  is also known to the manufacturer. 
     By the copies of the keys, a character sequence which is identical with the character sequence  24  has been encrypted and compressed in the same manner as is done in the control unit  10  by the encryption device  14  and the compressing device  16 . The manufacturer has been able to generate a key necessary for the encryption, identical with the key  34 , from the copies of the keys  26  and  30  from the database and the known character sequence  38 . The compressed encryption result has been inserted as VCRN in the unblocking code  22 . The compressed encryption result is still control-unit- and vehicle-specific to such a high degree that it is very improbable that a VCRN formed from a compressed encryption result is suitable for unblocking the control unit  10  in another passenger vehicle. 
     In order to be able to uninstall the control unit  10  and use it in another passenger vehicle, the control unit  10  has a receiving device  42  by which a vehicle-associated key  30 ′ of the passenger vehicle can be received and written into the memory  32 . 
     A receiving device such as the receiving device  42  can also be provided for writing into memory  28 . The control-unit-associated key  26  can then be specified at a later time, e.g. by the manufacturer of the motor vehicle instead of the manufacturer of the control unit  10 . 
     With each cross exchange of the control unit  10  between two passenger vehicles, a new VCRN is additionally generated for unblocking the control unit  10  for the respective passenger vehicles by the manufacturer of the passenger vehicle and provided to the user of the passenger vehicle for unblocking the control unit  10 . 
     In the case of a control unit such as the control unit  10 , it can also be provided to provide not only the one character sequence  24  but a plurality of different character sequences. A selective unblocking of different functionalities of the control unit via different unblocking codes is then possible. 
     However, the character sequence  24  can also be a value independent of the functionality to be unblocked. It is then possible to generate unblocking codes for different control units in a motor vehicle by one and the same character sequence. 
     The example shows how it is possible to check with a control unit whether the control unit is licensed to the passenger vehicle in which it is installed. 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide  v.  DIRECTV,  69 USPQ2d 1865 (Fed. Cir. 2004).