Abstract:
A method for the authentication of an RFID tag uses an asymmetric cryptography method which ensures protection against the recycling of authentication RFID tags and needs no deactivation of the corresponding RFID tag for this purpose. To this end, the certificate of an RFID tag to be checked is not stored on the RFID tag but is stored physically separately from the RFID tag. Firstly, the RFID reader reads the certificate of the RFID tag to be checked before the challenge-response protocol is carried out successfully with the RFID tag to be checked. Consequently, an RFID tag can be reused for authentication only when the certificate relating to this RFID tag is known.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2010/053732 filed Mar. 23, 2010, which designates the United States of America, and claims priority to German Application No. 10 2009 022 850.0 filed May 27, 2009. The contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a method and system for authentication of an RFID tag using an asymmetric cryptography method, which is especially suitable for preventing RFID tag recycling for product counterfeiting. 
       BACKGROUND 
       [0003]    Counterfeit products are becoming an ever greater problem with great economic implications, extending as far as danger to human health. In the case of counterfeited medicines there is even a danger to human life. 
         [0004]    To counter counterfeit medicines and recognize counterfeit medicines in circulation, in addition to characteristics that are difficult to copy, such as watermarks, seals or special color markings for example, so-called auto ID (Identification) technologies such as barcodes or RFID (Radio Frequency Identification) systems are used. In such cases there are in particular two approaches that are followed to detect counterfeit medicines with certainty. 
         [0005]    The first approach is based on a track-and-trace system in which the movements of a medicine are logged within the whole logistics chain. In such cases a globally unique serial number known as the Electronic Product Code (EPC) is read automatically by means of barcode or RFID and written into a central database when goods are dispatched and received. In order to now check whether an original medicine is involved, the data in the database is checked for consistency. If for example the same serial number occurs at two different locations at the same time, it is highly likely that the medicine has been counterfeited. However this approach has the problem of all participants in the delivery chain having to support this central database infrastructure. 
         [0006]    The second approach is based on a cryptographic authentication of the RFID tags. Conventional RFID chips with a serial number can be cloned easily by personalizing other RFID chips with precisely this serial number. Ultimately it is impossible to distinguish any longer between the original and the cloned RFID chip. Cryptographic RFID chips on the other hand use a cryptographically-secured authentication and can thus securely prevent the cloning of authentication information. To this end the RFID chip is no longer a pure data memory but automatically executes cryptographic algorithms which require the knowledge of secret key information. A particular advantage of this process is the authentication by means of asymmetric cryptographic methods in which no secret information is necessary in the RFID reader itself in order to perform the check. The RFID reader merely needs the public signature key of the brand manufacturer to check any given RFID chip in order to thus be able to check the validity of the individual public key received from the RFID chip. In decentralized infrastructures in particular there is thus the option of verifying the authenticity of RFID chips and thus also of the product, without any complex central key management or an online transaction being necessary to do this. 
         [0007]    However the disadvantage of this is that the RFID tags have to be deactivated after use. Otherwise the RFID tags from discarded blisters of an original medicine could be released and used again with a counterfeit medicine. A consequentially necessary deactivation by physical or protocol means, in addition to the technical outlay, always requires a deliberate action. Since the deactivation above all entails a benefit for the medicine manufacturer this merely entails extra expense for the user in the first instance. 
       SUMMARY 
       [0008]    According to various embodiments, a method for authentication of an RFID tag can be specified with an asymmetric cryptography method which guarantees protection against recycling of authentication RFID tags and needs no deactivation of the corresponding RFID tag for this purpose. 
         [0009]    According to an embodiment, in a method for authentication of an RFID (Radio Frequency Identification) tag by an RFID reader using a challenge-response protocol in accordance with an asymmetric cryptography method, the RFID tag is assigned a pair of keys with a private and at least one first public key, the key pair is assigned a digital signature for authentication of the first public key, the RFID reader device is authenticated on the basis of the first public key and the digital signature of the RFID tag, wherein the private key is stored on the RFID tag, and the first public key and the digital signature are stored physically separated from the RFID tag and are able to be detected automatically by a data capture device. 
         [0010]    According to a further embodiment, the first public key and the digital signature can be stored on a further RFID tag and the data capture device can be an RFID reader. According to a further embodiment, the first public key and the digital signature can be stored in the form of a barcode and the data capture device can be a barcode reader. According to a further embodiment, the authentication of the RFID tag may comprise the following steps: —Determination of the first public key and of the digital signature by the RFID reader, —Checking by the RFID reader of the validity of the first public key on the basis of the digital signature with a second public key of a key issuer, —Generation and wireless transfer of a challenge by the RFID reader, —Determination of a response based on the transferred challenge and the private key and transfer of the response by the RFID tag, —Authentication of the RFID tag by the RFID reader based on the transferred response. According to a further embodiment, a certificate may comprise the first public key and the digital signature. 
         [0011]    According to another embodiment, a system for authentication of an RFID tag, an RFID reader and a further data carrier may be configured to carry out an authentication method as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be explained in greater detail below with reference to exemplary embodiments and the figures, in which: 
           [0013]      FIG. 1  shows a flowchart of the method for authentication of an RFID tag by an RFID reader, 
           [0014]      FIG. 2  shows an example of an application of the system according to various embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    According to various embodiments, in a method for authentication of an RFID tag by an RFID reader using a challenge-response protocol according to the asymmetric cryptography method, the RFID tag is assigned a pair of keys with a private and at least one first public key. In addition the pair of keys is assigned a digital signature for authentication of the first public key. The RFID reader authenticates the RFID tag on the basis of the first public key and the digital signature. The private key in this case is stored on the RFID tag while the first public key and the digital signature are stored physically separately from the RFID tag and are able to be detected automatically by a data capture device. 
         [0016]    Data capture devices, without restricting the generality of this term, are devices for reading out data from data carriers. Data capture devices are for example handwriting readers, mark readers, barcode readers or RFID readers. In the broader sense this also includes software and devices which convert analog signals into digital data, such as scanners for images and text, frame grabbers for videos and voice recognition software for example. 
         [0017]    According to an embodiment, the authentication of the RFID tag comprises the following steps: The RFID reader determines the first public key and the digital signature and checks the validity of the first public key on the basis of the digital signature with a second public key of the key issuer. Subsequently the RFID reader generates and transfers a challenge to the RFID tag. The RFID tag determines a response on the basis of the transferred challenge and the private key and transfers this response to the RFID reader. On the basis of the response transferred the RFID reader finally authenticates the RFID tag. 
         [0018]    The system according to various embodiments for authentication comprises at least one RFID tag and an RFID reader which are configured to execute the above authentication method. 
         [0019]      FIG. 1  shows a flowchart of a method for authentication of an RFID tag  101  by an RFID reader  102  according to various embodiments. In this example the private key is stored on the RFID tag  101  to be authenticated while the public key and the digital signature assigned to the private key are stored on a further RFID tag  103 . 
         [0020]    By using an asymmetric cryptography method for authenticating an RFID tag the cloning of authentication information can be prevented. The RFID tag is now no longer a pure data memory, the contents of which would in principle be able to be copied and thus cloned. Through the challenge-response protocol the RFID tag automatically performs cryptographic algorithms which require the knowledge of secret key information. In order to be able to produce clones of the RFID tag in this scenario, an attacker must obtain knowledge of this secret key information, but this is stored in the RFID tag and safeguarded by hardware protection measures. 
         [0021]    For challenge-response protocols based on symmetrical cryptographic methods the RFID reader would also have to know the secret key information of the RFID chip to carry out the check. This information must either be expensively protected in the RFID reader or the RFID reader must have an online connection to a server on which the secret key is located. When asymmetrical cryptographic methods are used no secret information for performing the check is necessary in the RFID reader. Instead it is sufficient for the RFID reader to know the public key of the asymmetrical key pair consisting of public and private key of the RFID tag to be authenticated. In order to avoid the RFID reader having to store the public keys of all RFID tags to be checked, so-called certificates are generally used. In this certificate both the public key and also a corresponding digital signature is stored with which the validity of the public key can be checked by the recipient of the certificate. The respective certificate is provided for example by an RFID tag to be checked and is made available to the RFID reader on request. In this case for example the individual public keys of the individual RFID tags are digitally signed by the medicine manufacturer, so that to check the validity of a public key, the RFID reader must merely possess the corresponding public signature key of the medicine manufacturer. The validity of the individual public key for the RFID tag is then checked which is initially read out from the RFID tag. Subsequently the RFID tag verifies with the RFID reader, using the challenge-response protocol, that it possesses the associated private key. 
         [0022]    A possible sequence of the method is shown in  FIG. 1 . Initially the RFID reader  102  receives from the further RFID tag  103  the public key and the signature  104  of the RFID tag  101  to be checked. This signature is now checked by the RFID reader  102  with the aid of the public key of the medicine manufacturer. If the certificate obtained is valid, a challenge is generated by the RFID reader  102  and is transferred  105  to the RFID tag  101 . The RFID tag  101  in its turn generates a response based on its private key and the challenge received  106 . The response determined is transferred in its turn to the RFID reader  102 . With the aid of the public key of the RFID tag  101  to be checked, which the RFID reader  102  has determined from the certificate, the RFID reader  102  now checks the response received. If the response was correctly formed the RFID tag  101  has verified to the RFID reader  102  its knowledge of the necessary secret key information for forming the response by this and is accepted as authentic  108 . 
         [0023]    The decisive advantage with the asymmetric authentication method lies in the fact that any given RFID reader can check the authenticity of the RFID chip if it possesses the public signature key of the brand manufacturer. In decentralized infrastructures in particular this provides a simple opportunity for verifying the validity of RFID tags and thus also of the product without transactions having to be carried out online and without expensive key management having to be present. 
         [0024]    The certificate of an RFID tag to be checked is now not stored on this RFID tag but is stored physically separated from this RFID tag. Initially the RFID reader reads the certificate of the RFID tag to be checked before the challenge-response protocol is carried out successfully with the RFID tag to be checked. Consequently an RFID tag for authentication can only then be used again if the certificate for this RFID tag is known. 
         [0025]    By separating certificate and RFID tag to be checked the likelihood of an RFID tag being able to be employed again after use is decreased. A product counterfeiter is forced to obtain the corresponding certificate first of all. Once certificate and associated RFID tag are separated, for example by paper or other rubbish, the assignment has disappeared and the effort of assigning a found certificate to a found RFID tag again increases accordingly. 
         [0026]    An example of an application according to an embodiment is shown in  FIG. 2 . A packet of medicines  201  contains two blisters which are each equipped with an RFID tag for authentication. The two RFID tags each have the private key for the authentication. The associated certificates, comprising the respective public key and digital signatures, are not on the respective RFID tag  204  but are attached to the packaging of the medicines. For successful authentication by the RFID reader  205 , the RFID tag  204  with the private key and the RFID tag on the packaging  202  with the associated public key must thus be present in each case. 
         [0027]    In a further embodiment the certificate is printed in a two-dimensional barcode on the packaging and must be read by means of the barcode scanner before authentication. 
         [0028]    In a further embodiment the certificate of the first blister RFID tag is stored in the second blister RFID tag in the certificate of the second blister RFID tag in the first blister RFID tag. A medicine can then be successfully authenticated if all blisters are in the packaging. For a product counterfeiter this means that he would have to use the two corresponding blisters at once to counterfeit a product.