Patent Publication Number: US-6337912-B2

Title: Method of and system for writing-in key information

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method of and a system for writing key information transmitted securely from a central station to a remote station into a data carrier available at said remote station. In a preferred use the data carrier is a key for a motor vehicle, which key is to be issued to the legitimate owner of the motor vehicle by a dealer, for example because the owner requires an additional key or has lost a key originally received upon the purchase of the motor vehicle. However, it is to be noted that the method and the system in accordance with the invention are also suited for other uses, for example for keys giving access to certain rooms or areas. In general, the method and the system in accordance with the invention enable selected allocated information to be written into a data carrier in a secure manner. 
     When key information stored at a central station is to be written into a data carrier at a remote station it is necessary in conventional systems to ensure that the transmission of the key information to the remote station cannot be overheard, because otherwise an unauthorized person can write the illegally intercepted key information into a data carrier of his own and can thus, for example, gain unauthorized access to protected rooms or areas. The alternative, i.e. to write the key information into the data carrier at the central station and subsequently send it to the remote station, is also unfavorable because the data carrier can be stolen during transportation. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method of securely writing key information into a data carrier which is issued at another station than that where the key information is generated or has been stored. 
     According to the invention this object is achieved in that the key contains stored identification information which cannot be read externally and is consequently secret, and in that the key information is encrypted with this identification information at the central station and the encrypted information is transferred to the data carrier at the issuing station. In the data carrier this encrypted key information is subsequently decrypted and stored. 
     This method has the advantage that the data carriers can be despatched freely because they do not contain any key information, so that a thief cannot abuse the data carrier. The unauthorized interception of the transmitted encrypted key information is neither of any avail to an unauthorized person if he does not have a data carrier with the correct identification information into which he can write the encrypted key information. 
     In this respect is important that each data carrier contains open further identification information, which is readable. Thus, it is possible to store in each data carrier individual identification information which differs from that in the other data carriers, the relationship between the open further identification information and the secret identification information being stored at the central station. Owing to this measure encrypted key information can be decrypted correctly by means of only one, i.e. the correct, data carrier. 
     In order to enable the allocation of secret identification information, key information and the open further identification information to be organized more easily, it is effective if the identification information and the open identification information are written into the data carrier at a further station before the data carrier is conveyed to the remote station. This further station should then be coupled to the central station via a protected information transmission link, so as to enable the same information to be written in at this station. The further station can also be identical to the central station. 
     The key information to be transmitted to the data carrier is assigned unambiguously to at least one individual object, for example a motor vehicle. When a data carrier is to be assigned to such an individual object the object information characterizing this object should be transmitted to the central station. In order to also protect this transmission path it is effective to encrypt the object information with the open further identification information prior to the transmission to the central station. 
     For data encryption a variety of methods are known. A particularly simple encryption and decryption of the key information and the objection information, which can be used in the method in accordance with the invention, is by exoring with the identification information. Since the identification information is secret, decryption is not possible without the key information being known even if the encryption method is known. 
     In addition to or instead of the encryption by means of an Exclusive-Or operation an asymmetrical encryption process can be used for encrypting the object information prior to transmission from the remote station to the central station, the open key being used for the encryption of the object information or the encrypted object information, decryption at the central station being effected by means of the secret key of the asymmetrical encryption process. 
     The invention further relates to a system for writing key information transmitted securely from a central station to a remote station into a data carrier available at said remote station, and to a data carrier and a terminal for use in such a system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The Sole FIGURE shows a system for writing key information, that is securely received from a central station, into a data carrier at a remote station. 
    
    
     The Sole FIGURE shows a system for writing key information, that is securely received from a central station  20 , into a data carrier  10 ′ at a remote station  40 . The central station  20  has two memories  21  and  25 . The memory  21  comprises two groups  22  and  23  of storage locations, which are associated with one another in pairs. By addressing a storage location of the group  23  with given information, i.e. open identification information of a given data carrier in the case of data carriers with individually distinct identification information or the specification of a data carrier group in the case of data carriers with identical identification information per group, this associated identification information is read from the associated storage location of the group  22 . 
     Similarly, the memory  25  in the present example comprises three groups  26 ,  27  and  28  of storage locations. The storage locations of the group  26  store object information and each of these storage locations is associated with a given storage location of the group  27 , which given storage location stores key information associated with this object. Furthermore, each storage location of the group  26  is preferably associated with a plurality of storage locations of the group  28 , which storage locations store a plurality of identification numbers. Their meaning will be explained in some detail hereinafter. 
     A data carrier  10  is situated at a further station. It is obvious that in practice many data carriers are available, which are of mutually identical construction and of which the data carrier  10  shown here is representative. This data carrier  10  includes a processing unit  11  and four storage locations  12  to  15 . The storage location  12  serves for storing identification information which can only be processed internally in the data carrier  10  and which is never made available externally. The storage location  13  stores open further information which characterizes the individual data carrier and which can be read out externally. Preferably, these two types of information are supplied by the central station  20 , where they are written into two mutually associated storage locations  22  and  23  of the memory  21  and the respective information is written into the storage locations  12  and  13  at the further station, where the data carrier  10  is situated initially. The further station can be identical to the central station  20 . 
     This writing into the storage locations  12  and  13  is effected for a multiplicity of data carriers and these data carriers are subsequently conveyed to a remote station via a transport path. This transport path has at least an unprotected part, shown as a dash-dot line  39 . In this part of the transport path the data carriers could be stolen. However, such a theft cannot give rise to any substantial damage because the data carriers do not yet contain any key information and therefore cannot be used at an object. 
     If key information for a given object is to be written into a data carrier at the remote location, i.e. into the data carrier  10 ′, which is shown in more detail in the FIGURE, this data carrier  10 ′ is coupled to a terminal  40 . As a result, the open identification information is read from the storage location  13 ′ and is applied to the terminal  40  via the connection  43 . Moreover, object information is entered via an input  41 , for example by means of a keyboard. These two types of information are applied to an encryption device, which in the present case comprises two sections  42  and  44 . 
     In the present case the section  42  of the encryption device takes the form of an Exclusive-Or element. The encrypted information, i.e. the object information encrypted with the open identification information, is applied to a section  44 , which performs an asymmetrical encryption, for example in accordance with the RSA method, with a fixed key, which is shown here as being applied via an input  45 . The key need not be secret because decryption is not possible with the aid of this key. 
     The additional encryption with the open identification information results in a substantially improved protection. It is now assumed that the data transmitted by a workshop, i.e. encrypted object information and open identification information, is intercepted by an unauthorized person who possesses preprogrammed keys. If this unauthorized person transmits the same encrypted object information, with the open identification information of his key but without the encryption with the open identification information, he would obtain the key information for the object information which has been encrypted with the secret identification information of his key and which is therefore correctly decrypted in the key, so that a valid key for the object is obtained illegally. Owing to the additional encryption with the open identification information the encrypted object information transmitted by the unauthorized person will not be decrypted correctly at the central station, so that the desired key information is not read correctly from the memory  25 . However, if the unauthorized person transmits the likewise intercepted open identification information, he will merely obtain key information which has not been encrypted with the secret identification information stored in his key and which therefore cannot be decrypted. Thus, by tapping an authorized transmission it is not possible to obtain data for an object by means of which a key for the same object can be generated without authorization. 
     Similarly to the open identification information the encrypted information supplied by the section  44  via the line  47  is now transferred to the central station  20  via the line  43 . This transfer can be effected via an non-protected path because the encrypted information on the line  47  cannot be decrypted without the secret key of the asymmetrical encryption being known and the open identification information does not include any direct reference to the key information required in the data carrier. 
     In the central station  20  the encrypted information on the line  47  is applied to a decryption device comprising the sections  32  and  34 . In the section  34  the information transferred via the line  47  is decrypted by means of a secret key, shown here as being applied via an input  35 . The information appearing on the output  37  of the section  34  of the decryption device is then the same as that on the output of the Exclusive-Or element  42  in the terminal  40 . However, this is not yet the object information applied via the input  41  of the terminal  40 . Therefore, the line  37  leads to an Exclusive Or element  32 , having a further input to which the open identification information is applied via the line  43 . Now the decrypted object information, which is applied to the memory  25 , is available on the output  33  of the Exclusive Or element  32 . In the group  26  that storage location is selected in which this object information has been stored and the key information is read from the associated storage location of the group  27 . Moreover, the open identification information on the line  43  controls the memory  21 , in that the storage location of the group  22  in which this identification information has been stored, is addressed and the associated storage location of the group  22  in which the secret identification information has been stored, is read out. 
     The information read from the memory  25  is applied to an encryption circuit  30 , which also takes the form of an Exclusive-Or element. The information appearing on the output  31  is transmitted to the remote station, which is effected via a transmission path which need not be protected because the decrypted key information can only be recovered from the information on the line  31  with the aid of the correct secret identification information, but this information is hidden in the data carrier and is not transmitted directly. 
     Moreover, in the present example an identification number is read from an associated storage location of the group  28  and is transmitted to the remote station via the line  38 , for which also a non-protected path can be used. 
     In the remote station the information on the line  31  and on the line  38  is applied to the data carrier  10 ′ via the terminal  40 . The identification number on the line  38  is written directly into the storage location  15 ′ in the data carrier  10 ′, while the encrypted key information on the line  31  is applied to a decryption device  17 , which receives the secret identification information from the storage location  12 ′ on a further input. This decryption device is again an Exclusive Or element and generates the decrypted key information on its output, which key information is written into the storage location  14 ′. Thus, the data carrier  10 ′ receives all the information necessary for its use in conjunction with a given object, for example a motor vehicle, without the possibility of an unauthorized interception of the essential key information during transmission. 
     The identification number in the storage location  15 ′ is not strictly necessary for the described method and, in the case that the data carrier is a key for a motor vehicle, this identification number serves for initially checking in the motor vehicle whether the key is permissible before it is ascertained whether an authorized key is used. The reason for this is that if by means of a non-authorized key, i.e. one with incorrect key information, a number of starting attempts have been made, all the functions of the motor vehicle are permanently disabled and can be restored only by means of a specific secret procedure. Thus, the identification number ensures that by means of a wrong key, which for example belongs to another motor vehicle and consequently contains other key information, no false starting attempts, otherwise recognized as permissible, can be made. 
     Suitably, each key authorized for a motor vehicle carries a different identification number, for which reason a plurality of identification numbers corresponding to the respective object information are stored in the memory  25  and in the associated object. 
     It is obvious that the encryption in the terminal  40  by means of the sections  42  and  44  and the corresponding decryption in the central station can also be effected in another manner than shown. The essential feature is that the information on the line  47  is encrypted in such a manner that a decryption by the transmitted information alone is not possible.