Abstract:
A method for authentication of a user towards a unit (AR 1 ) is described that uses unique biometric data of the user but avoids spreading of the sensitive biometric data. The method overcomes the problem of the lack of trustworthiness of a client (C 1 ) operated by a user and the lack of trustworthiness of a unit (AR 1 ) operated by an institution offering services or goods introducing an authentication instance (AI 1 ) operated by a third party that is trusted by both the user operating the client (C 1 ) and the institution operating the unit. According to the invented method the responsability for the secure handling of the sensitive biometric data is taken from the institution operating the unit (AR 1 ) requesting authentication and given to a trusted third party organization operating an authentication instance (AI 1 ). The authentication instance (AI 1 ) stores the sensitive biometric data and performs the authentication based on a pattern matching of a prestored pattern of biometric data and a pattern of biometric data recorded by the user.

Description:
FIELD OF INVENTION  
         [0001]    The invention relates to a method for the safe use and transmission of biometric data to authenticate a user towards a unit via a client. The invention further relates to a client, a unit, and an authentication instance to perform said method.  
         DESCRIPTION OF PRIOR ART  
         [0002]    A large number of applications exist where authentication of a user is required, for example access-systems or online banking. The mostly applied methods for authentication are possession of a physical object e.g. a key or a card or the use of confidential information e.g. a Personal Identification Number PIN or a password, stored at an authentication instance and known to the user.  
           [0003]    A disadvantage of the usage of physical objects is that they can be lost by or stolen from the user.  
           [0004]    As users are given several passwords in different contexts, many users write down their passwords in this way degrading the trustworthiness of the confidential information.  
           [0005]    Therefore a need for safer authentication methods that overcome the disadvantages of the usage of physical objects or confidential information exists.  
           [0006]    Another known method for authentication is the usage of biometric characteristics of a user. Biometric authentication is a method to identify a person unambiguously based on unique individual anatomical patterns as iris, retinal skin, fingerprints, hand geometry, ears or face or characteristic individual behavior of the user e.g. voice or handwriting.  
           [0007]    The term biological pattern refers to anatomical patterns as well as patterns of individual behavior.  
           [0008]    A biological pattern is measured using for example a camera, a laser-scanner, a microphone or a pressure-sensitive pen and the resulting signal is recorded.  
           [0009]    In the following the term biometric data refers to data stemming from the measurement of some biological pattern. The term pattern of biometric data refers to biometric data stemming from the measurement of a particular biological pattern e.g. a picture of the fingerprint of the right thumb of a user.  
           [0010]    In said authentication methods, a recorded pattern of biometric data is compared to a prestored pattern of biometric data of the user. If the recorded pattern of biometric data and the prestored pattern of biometric data match to a sufficient degree, the user is authenticated. Biometric techniques could offer a convenient method for authentication that overcomes the disadvantages of the usage of physical objects and confidential information. Said techniques are described in more detail in “Biometrics” by Anil Jain, Ruud Bolle and Sharath Pankanti, Kluver Academic Publishers, 1998.  
           [0011]    Today&#39;s biometric authentication methods are based on closed systems, comprising the measurement device, a biometric data storage, a comparison unit capable of comparing a recorded pattern of biometric data with a prestored pattern of biometric data. Using biometric for authentication towards different institutions would require installing several such closed systems. This would implicate spreading of the biometric data and means an enhanced risk of one of the biometric data storages to be forced open and biometric data to be revealed.  
           [0012]    As biometric data are unique they cannot be exchanged. As the number of biological patterns of one user is limited, patterns of biometric data cannot be marked invalid arbitrarily often, when they are revealed. This means that biometric data are sensitive data. The demand on their secure handling is therefore high and spreading of biometric data is undesirable.  
           [0013]    Therefore it is object of the invention to provide a method for the authentication of a user towards a unit using biometric data that avoids spreading of the biometric data.  
         SUMMARY OF THE INVENTION  
         [0014]    This object is achieved by the methods of claims  1 ,  2 ,  5  and  9 , the unit of claim  11  the authentication instance of claim  12 , the client of claim  14 , and the software of claim  17 , claim  18 , and claim  19 .  
           [0015]    Advantageous embodiments are described in dependent claims.  
           [0016]    The term client refers to any kind of user operated device that is capable of performing a communication with the user, wherein an authentication of the user is one objective of the communication. Examples for clients are a user interface of a vending machine or a cash dispenser, a personal computer, or a mobile station of a user of a telecommunication network.  
           [0017]    The term unit refers to any kind of device requesting authentication of a user. Examples for units are units offering services or goods to a user e.g. a vending machine, a cash dispenser or a server offering a service or enabling bank accounts.  
           [0018]    The client and the unit do not need to be physically separated i.e. the terms also refer to a device capable of performing a communication with a user and requesting authentication of the user, e.g. a vending machine or a cash dispenser comprising a user interface.  
           [0019]    The term authentication instance refers to a server operated by a trusted third party, storing at least one pattern of biometric data for each user.  
           [0020]    The proposed method comprises a sequence of messages exchanged between the client C 1 , C 2 , C 3 , the unit AR 1 , AR 2 , AR 3  and the authentication instance AI 1 , AI 2 , AI 3  and processing steps performed at the client C 1 , C 2 , C 3  and the authentication instance AI 1 , AI 2 , AI 3 . The client C 1 , C 2 , C 3  is requested  1 ,  32 ,  41 , preferably by the unit AR 1 , AR 2 , AR 3 , to initiate authentication. Afterwards the authentication instance AI 1 , AI 2 , AI 3  is requested  3 ,  33 ,  42  to perform the authentication. The request can be for example sent  2 ,  32 ,  42  by the client C 1 , C 2 , C 3 . The client C 1 , C 2 , C 3  is then requested  4 ,  34 ,  43 , for example by the authentication instance AI 1 , AI 2 , AI 3 , to send biometric data of the user in order to authenticate said user. A pattern of biometric data of the user is recorded using a measurement device. Preferably the pattern is recorded by the client C 1 , C 2 , C 3 . The pattern of biometric data is encrypted and sent  5 ,  36 ,  44  to the authentication instance AI 1 , AI 2 , AI 3 , for example by the client C 1 , C 2 , C 3 . The authentication instance AI 1 , AI 2 , AI 3  decrypts the received data and performs a comparison of the decrypted data to a prestored pattern of biometric data of the user.  
           [0021]    The authentication instance AI 1 , AI 2 , AI 3  sends  6 ,  37 ,  45  a result of the comparison, for example to the unit AR 1 , AR 2 , AR 3 .  
           [0022]    It is an advantage of the proposed method that the user can ask for authentication towards different units without needing to reveal her sensitive biometric data to the units but reveal sensitive biometric data only once to the authentication instance AI 1 , AI 2 , AI 3 .  
           [0023]    Another advantage is that an institution that is not willing to or able to take care for the secure handling of biometric data of its users can use biometric data for authentication of its users.  
           [0024]    It is further advantageous that the unit AR 1 , AR 2 , AR 3  can accept authentication via different clients without needing to trust a message from a client C 1 , C 2 , C 3  acknowledging the authentication of the user.  
           [0025]    Further advantageous is a method wherein the unit AR 1 , AR 2  relays signals between the authentication instance AI 1 , AI 2  and the client C 1 , C 2 . This has the advantage that the unit AR 1 , AR 2  does not receive messages from an unknown party.  
           [0026]    Further advantageous is the storage of a plurality of patterns of biometric data for each user and a selection of one of said patterns of biometric data for the authentication process according to the proposed method. In that case the request to send biometric data contains an identification of the selected pattern of biometric data, and the user is user is requested to send biometric data matching to the selected pattern. The received pattern of biometric data is then compared to the selected pattern of biometric data. This reduces the value of a single pattern of biometric data picked up by an eavesdropper. Furthermore the trustworthiness of a pattern of biometric data received by the authentication instance AI 1 , AI 2 , AI 3  is enhanced.  
           [0027]    Further advantageous is the encryption of the request to send biometric data containing the identification of the selected pattern. This reduces the value of a set of patterns of biometric data picked up by an eavesdropper even if the eavesdropper is in possession of several patterns of biometric data of a user. Thus the trustworthiness of a pattern of biometric data received by the authentication instance AI 1 , AI 2 , AI 3  is further enhanced.  
           [0028]    Further advantageous is the extraction of significant characteristics of the pattern of biometric data before encrypting them. This has two advantages: Firstly the amount of data to be transmitted for signalling purposes is reduced. Secondly a recorded sample of biometric data picked up by an eavesdropper is of no account if the eavesdropper is not in possession of the algorithm for extracting significant characteristics of the biometric data.  
           [0029]    Further advantageous is the usage of a number allowing a hardware identification of the client C 1 , C 2 , C 3  in the message sending the encrypted pattern of biometric data to the authentication instance AI 1 , AI 2 , AI 3 . Thus the trustworthiness of the message sending encrypted biometric data is enhanced.  
           [0030]    The invented authentication instance AI 1 , AI 2 , AI 3  adapted to perform the related steps of the proposed method comprises an input/output unit IO-U 1  for exchanging messages and data, a decryption unit DU for decrypting biometric data, a biometric data storage BDS, storing at least one pattern of biometric data for each user, a comparison unit CU for comparing two patterns of biometric data, and a processing unit PU for processing information and coordinating the units.  
           [0031]    In order to be able to encrypt outgoing messages, e.g. the request to send biometric data, the authentication instance AI 1 , AI 2 , AI 3  additionally comprises a message encryption unit MEU.  
           [0032]    The client C 1 , C 2 , C 3  adapted to perform the related steps of the proposed method comprises an input/output unit IO-U 2 , receiving information from and sending information to communication network parts, a measurement device MD, recording patterns of biometric data of a user, an encryption unit EU encrypting biometric data, a user interface device UI for exchanging information between the user and the client C 1 , C 2 , C 3 , and a central processing unit CPU, processing information and coordinating the units.  
           [0033]    It is advantageous, if the client C 1 , C 2 , C 3  additionally comprises a feature extraction unit that is capable of extracting significant characteristics of the recorded pattern of biometric data.  
           [0034]    In order to provide a number for hardware identification a client C 1 , C 2 , C 3  can additionally comprise a hardware identification memory HWID, storing a hardware identification number.  
           [0035]    It is preferable to perform the steps of the proposed method that are related to the authentication instance AI 1 , AI 2 , AI 3  such that a software program that is loaded into the authentication instance AI 1 , AI 2 , AI 3  controls the authentication instance AI 1 , AI 2 , AI 3  in a way that it performs the related steps.  
           [0036]    It is preferable to perform the steps of the proposed method that are related to the client C 1 , C 2 , C 3  such that a software program that is loaded into the client C 1 , C 2 , C 3  controls the client C 1 , C 2 , C 3  in a way that it performs the related steps.  
           [0037]    It is preferable to perform the steps of the proposed method that are related to the unit AR 1 , AR 2 , AR 3  such that a software program that is loaded into the unit AR 1 , AR 2 , AR 3  controls the unit AR 1 , AR 2 , AR 3  in a way that it performs the related steps. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    [0038]FIG. 1: shows an architecture using the invented method,  
         [0039]    [0039]FIG. 2: shows a signal flow for the use of the invented method,  
         [0040]    [0040]FIG. 3: shows an alternative signal flow for the use of the invented method,  
         [0041]    [0041]FIG. 4: shows a further alternative signal flow for the use of the invented method,  
         [0042]    [0042]FIG. 5: shows an authentication instance according to the invention, and  
         [0043]    [0043]FIG. 6: shows a client according to the invention.  
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0044]    In the following the invention is described in more detail by means of embodiments and figures. Equal reference signs indicate equal elements.  
         [0045]    [0045]FIG. 1 depicts an example of an architecture using the invented method. It shows a client C 1  connected to a unit AR 1  via a communication link, said unit being connected to an authentication instance AI 1  via another communication link.  
         [0046]    The communication links are depicted as arrows.  
         [0047]    In a further embodiment of the invention, also a connection via a third communication_link between the client C 1  and the authentication instance AI 1  exists. A communication link can be a communication link by wire or a wireless communication link or a combination of both.  
         [0048]    In a preferred embodiment the connections are network connections using a computer network, e.g. an Internet Protocol (IP)-based network or network connections using a telecommunication network e.g. a Universal Mobile Telecommunication System (UMTS)-network or a Global System for Mobile-Communications (GSM)-network.  
         [0049]    The authentication instance AI 1  stores at least one pattern of biometric data. In a preferred embodiment of the invention, the authentication instance AI 1  stores a plurality of patterns of biometric data for each user.  
         [0050]    The authentication instance can be for example a server in an IP-based network. The authentication instance is operated by a trusted third party institution that is trusted by both the user operating the client and the institution operating the unit. The trusted third party is, for example, a bank, a credit card company, a telecommunication network operator or a company specialised on authentication services.  
         [0051]    [0051]FIG. 2 depicts a signal flow according to the invented method. The figure depicts a client C 1 , a unit AR 1  requesting an authentication, a client C 1  and an authentication instance AI 1 . In a first step, the unit AR 1  requests the client C 1  to start the user authentication process in a message  1 .  
         [0052]    In a next step the client C 1  requests authentication of its user by sending a message  2  to the unit AR 1 . Said message comprises an identification of the user and of the authentication instance AI 1 . If the authentication instance AI 1  is a server in an IP based network, the identification of the authentication instance AI 1  can be its IP address or its URL. If the client C 1  is a mobile station of a telecommunication network user, the identification of the user can be her M-ISDN number.  
         [0053]    In the example of the cash dispenser the identification of the user could be her account number.  
         [0054]    In a next step, the unit AR 1  requests the authentication instance AI 1  to prompt the user for authentication by sending a message  3 . The user is identified towards the authentication instance AI 1  for example by its identification sent in message  2 .  
         [0055]    In a preferred embodiment of the invention, the authentication instance AI 1  randomly selects one of a plurality of the stored patterns of biometric data for the user of client C 1 . This can be for example a pattern of biometric data, relating to the pattern of a certain word said by the user, or relating to one of ten possible fingerprints.  
         [0056]    In the next step, the authentication instance AI 1  sends a message  4  via the unit AR 1  to the client C 1  in order to prompt the user for authentication. The message  4  comprises a prompt value, indicating which pattern the authentication instance requests.  
         [0057]    In a preferred embodiment of the invention, the content of the message  4  is encrypted, so that only the client C 1  is able to decrypt it, for example using a symmetric key known only to the client C 1  and the authentication instance AI 1 . Said key can be defined during the storage of biometric data.  
         [0058]    In a preferred embodiment of the invention the message  4  comprises a random number, which is used once for the transmission in order to prevent replay attacks. Said singularly used random numbers are known for example as transaction numbers from online banking systems.  
         [0059]    In another embodiment, the random number is not sent but calculated locally at client C 1  and authentication instance AI 1 , both of them using a random number generator with the same seed. The synchronisation of the random numbers can be achieved by sending a sequence number in the message  4 .  
         [0060]    In the case that the message has been encrypted, the client C 1  decrypts the message  4  in a next step.  
         [0061]    In the next step, the client C 1  prompts its user for authentication and requests the user to record a certain pattern of biometric data according to the prompt value of message  4 .  
         [0062]    In a preferred embodiment the client C 1  reduces the recorded pattern of biometric data to its significant characteristics. The algorithm reducing the recorded pattern to its significant characteristics can be changed regularly or in case of a detection of a weak link.  
         [0063]    The client C 1  encrypts either the recorded pattern of biometric data or in the case the pattern has been reduced to its significant characteristics the client C 1  encrypts said significant characteristics.  
         [0064]    The encryption is such that only the authentication instance AI 1  is able to decrypt the pattern of biometric data respectively its significant characteristics.  
         [0065]    In a preferred embodiment of the invention, the pattern of biometric data respectively its significant characteristics are encrypted by combination with a random number in the client C 1 , for example through XOR.  
         [0066]    The encrypted pattern of biometric data respectively its encrypted significant characteristics are sent in a message  5  to the authentication instance AI 1  via the unit AR 1 .  
         [0067]    In an embodiment of the invention, the message  5  comprises also a hardware authentication mechanism to identify the client C 1 . If the client C 1  is the mobile station of a GSM or a UMTS network user, said hardware authentication mechanism can for example be based on the International Mobile Subscriber Identity IMSI stored on a Subscriber Identity Module (SIM) respectively a Wireless Identity Module (WIM).  
         [0068]    In a next step, the authentication instance decrypts the message  5  thus obtaining the recorded pattern of biometric data respectively its significant characteristics. The decrypted pattern of biometric data is then compared to the prestored pattern of biometric data. In the case the recorded pattern of biometric data has been reduced to its significant characteristics the significant characteristics of the recorded pattern are compared with the significant characteristics of a prestored pattern of biometric data.  
         [0069]    Based on the result of the comparison the authentication is successful or not. A message  6  stating whether the authentication has been successful or not is sent to the unit AR 1 .  
         [0070]    In an embodiment of the invention, the unit AR 1  relays the result also to the client C 1  in order to inform the user in a message  7 .  
         [0071]    It is an advantage of the implementation depicted in FIG. 2 that the unit AR 1  contacts the authentication instance AI 1  and forwards messages sent between the client C 1  and the authentication instance AI 1 . By this, the unit AR 1  is certain that it does not receive fraudulent messages from an unknown party.  
         [0072]    [0072]FIG. 3 depicts an alternative signal flow according to the invention. The figure depicts a client C 2 , a unit AR 2  requesting an authentication of the client C 2  and an authentication instance AI 2 .  
         [0073]    In a first step, the unit AR 2  requests the client C 2  to start the user authentication process in a message  31 .  
         [0074]    In a next step the client C 2  requests authentication of its user sending a message  32 . Said message comprises an identification of the user and of the authentication instance AI 2 . If the authentication instance AI 2  is a server in an IP based network, the identification of the authentication instance AI 2  can be its IP address or its Uniform Resource Locator (URL). If the client C 2  is a mobile station of a telecommunication network, the identification of the user can be her M-ISDN number. In a next step, the unit AR 2  asks the authentication instance AI 2  to prompt the user for authentication by sending a message  33 . The user is identified towards the authentication instance AI 2  for example by its identification sent in message  32 .  
         [0075]    In a preferred embodiment of the invention, the authentication instance AI 2  randomly selects one of a plurality of the stored patterns of biometric data for the user of client C 2 . This can be for example a pattern of biometric data relating to the pattern of a certain word said by the user or to one of ten possible fingerprints.  
         [0076]    In a next step, the authentication instance AI 2  sends a message  34  to the client C 2  in order to prompt the user for authentication. The message  34  comprises a prompt value, indicating which pattern the authentication instance requests.  
         [0077]    In a preferred embodiment of the invention the content of the message  34  is encrypted so that only the client C 2  is able to decrypt it, for example using a symmetric key known only to the client C 2  and the authentication instance AI 2 . Said key can be defined during the storage of biometric data.  
         [0078]    In a preferred embodiment of the invention the message  34  comprises a random number, which is used once for the transmission in order to prevent replay attacks. Said singularly used random numbers are known for example as transaction numbers from online banking systems.  
         [0079]    In an alternative embodiment, the random number is not sent but calculated locally at client C 2  and authentication instance AI 2 , both of them using a random number generator with the same seed. The synchronisation of the random numbers can be achieved by sending a sequence number in the message  34 .  
         [0080]    In the case the message has been encrypted, the client C 2  decrypts the message  34  in a next step.  
         [0081]    In the next step, the client C 2  prompts its user for authentication and requests the user to record a certain pattern of biometric data according to the prompt value of message  34 .  
         [0082]    In a preferred embodiment the client C 2  reduces the recorded pattern of biometric data to its significant characteristics. The algorithm reducing the recorded pattern to its significant characteristics can be changed regularly or in case of a detection of a weak link.  
         [0083]    The client C 2  encrypts either the recorded pattern of biometric data or in the case the pattern has been reduced to its significant characteristics the client C 2  encrypts said significant characteristics.  
         [0084]    The encryption is such that only the authentication instance AI 2  is able to decrypt the pattern of biometric data respectively its significant characteristics.  
         [0085]    In a preferred embodiment of the invention, the pattern of biometric data respectively its significant characteristics are encrypted by combination with a random number in the client C 2 , for example through XOR.  
         [0086]    The encrypted pattern of biometric data respectively its encrypted significant characteristics are sent in a message  35  to the unit AR 2  that forwards the message to the authentication instance AI 2  in a message  36 .  
         [0087]    Instead of the two messages  35  and  36  a single message containing the encrypted pattern of biometric data can be sent directly from the client C 2  to the authentication instance AI 2 .  
         [0088]    In an embodiment of the invention, the messages  35  and  36  comprise also a hardware authentication mechanism to identify the client C 2 . If the client C 2  is the mobile station of a GSM or a UMTS network user, said hardware authentication mechanism can for example be based on the International Mobile Subscriber Identity IMSI stored on the Subscriber Identity Module (SIM) respectively the Wireless Identity Module (WIM).  
         [0089]    In a next step, the authentication instance decrypts the message  36  thus obtaining the recorded pattern of biometric data respectively its significant characteristics. The decrypted pattern of biometric data is then compared to the prestored pattern of biometric data. In the case the recorded pattern of biometric data has been reduced to its significant characteristics the significant characteristics of the recorded pattern are compared with the significant characteristics of a prestored pattern of biometric data.  
         [0090]    Based on the result the authentication is successful or not. The result of the process is sent to the unit AR 2  in a message  37 .  
         [0091]    In an embodiment of the invention, the unit AR 2  relays the result also to the client C 2  in order to inform the user in a further message.  
         [0092]    It is an advantage of the implementation depicted in FIG. 3 that the message requesting a specific pattern of biometric data to be send is not known to the unit. Thus the unit cannot reveal the relationship between the specification of the pattern of biometric data to be sent and the pattern of biometric data itself. In the case that significant characteristics have been extracted from the biometric data the relationship between the significant characteristics to be sent and the related specification cannot be revealed.  
         [0093]    [0093]FIG. 4 depicts an alternative signal flow according to the invention. The figure depicts a client C 3 , a unit AR 3  requesting an authentication, a client C 3  and an authentication instance AI 3 .  
         [0094]    In a first step, the unit AR 3  requests the client C 3  to start the user authentication process in a message  41 .  
         [0095]    In a next step the client C 3  requests authentication of its user by sending a message  42  to the authentication instance, said message comprising an identification of the user.  
         [0096]    If the client C 3  is the mobile station of a telecommunication network user, the identification of the user can be her M-ISDN number.  
         [0097]    In a preferred embodiment of the invention, the authentication instance AI 3  randomly selects one of a plurality of the stored patterns of biometric data for the user of client C 3 . This can be for example a pattern of biometric data relating to the pattern of a certain word said by the user, or relating to one of ten possible fingerprints.  
         [0098]    In a next step the authentication instance AI 3  sends a message  43  to the client C 3  in order to prompt the user for authentication. The message  43  comprises a prompt value, indicating which pattern the authentication instance requests. The prompt value requests the user to record biometric data relating to a certain biological pattern, for example to a print of a particular finger or to the voice pattern of a particular word.  
         [0099]    In a preferred embodiment of the invention, the content of the message  43  is encrypted so that only the client C 3  is able to decrypt it, for example using a symmetric key known only to the client C 3  and the authentication instance AI 3 . Said key can be defined during the storage of biometric data.  
         [0100]    In a preferred embodiment of the invention, the message  43  comprises a random number, which is used once for the transmission in order to prevent replay attacks. Said singularly used random numbers are known for example as transaction numbers from online banking systems.  
         [0101]    In an alternative embodiment, the random number is not sent but calculated locally at the client C 3  and the authentication instance AI 3 , both of them using a random number generator with the same seed. The synchronisation of the random numbers can be achieved by sending a sequence number in the message  43 .  
         [0102]    In the case that the message has been encrypted the client C 3  decrypts the message  43  in a next step.  
         [0103]    In the next step the client C 3  prompts its user for authentication and requests the user to record a certain pattern of biometric data according to the prompt value of message  43 . In a preferred embodiment the client C 3  reduces the recorded pattern of biometric data to its significant characteristics. The algorithm reducing the recorded pattern to its significant characteristics can be changed regularly or in case of a detection of a weak link.  
         [0104]    The client C 3  encrypts either the recorded pattern of biometric data or in the case the pattern has been reduced to its significant characteristics the client C 3  encrypts said significant characteristics.  
         [0105]    The encryption is such that only the authentication instance AI 3  is able to decrypt the pattern of biometric data respectively its significant characteristics.  
         [0106]    In a preferred embodiment of the invention, the pattern of biometric data respectively its significant characteristics are encrypted by combination with a random number in the client C 3 , for example through XOR.  
         [0107]    The encrypted pattern of biometric data, respectively its encrypted significant characteristics, are sent in a message  44  to the authentication instance.  
         [0108]    In an embodiment of the invention, the messages  44  comprises also a hardware authentication mechanism to identify the client C 3 . If the client C 3  is the mobile station of a GSM or a UMTS network user, said hardware authentication mechanism can for example be based on the International Mobile Subscriber Identity IMSI stored on the Subscriber Identity Module (SIM) respectively the Wireless Identity Module (WIM).  
         [0109]    In a next step, the authentication instance decrypts the message  44  thus obtaining the recorded pattern of biometric data respectively its significant characteristics. The decrypted pattern of biometric data is then compared to the prestored pattern of biometric data. In the case the recorded pattern of biometric data has been reduced to its significant characteristics the significant characteristics of the recorded pattern are compared with the significant characteristics of a prestored pattern of biometric data.  
         [0110]    Based on the result of the comparison the authentication is successful or not. The result of the process is sent to the unit AR 3  in a message  45 .  
         [0111]    In an embodiment of the invention, the unit AR 3  relays the result also to the client C 3  in order to inform the user in a further message.  
         [0112]    It is an advantage of the implementation depicted in FIG. 3 that the authentication instance AI 3  and the client C 3  exchange messages for the authentication directly. By this, a fraudulent unit AR 3  cannot tap the exchanged data.  
         [0113]    [0113]FIG. 5 depicts a hardware architecture of an authentication instance according to the invention. In the context of a telecommunication network, for example a GSM network or a UMTS network, said architecture could be part of an authentication centre. In the context of an IP network the depicted architecture could be part of a server used for authentication purposes.  
         [0114]    The authentication instance comprises an input/output unit IO-U 1 , a message encryption unit MEU, a decryption unit DU, a biometric data storage BDS, a comparison unit CU, and a processing unit PU.  
         [0115]    The task of the input/output unit IO-U 1  is to connect the authentication instance to other entities. In the case that an IP based network is used, the input/output unit IO-U 1  could be a network interface card. The processing unit PU is connected to the input/output unit IO-U 1  and the message encryption unit MEU.  
         [0116]    The task of the message encryption unit MEU is to encrypt outgoing messages. It is connected to the input/output unit IO-U 1  and the processing unit PU.  
         [0117]    The input/output unit IO-U 1  is connected to a comparison unit CU via the decryption unit DU. The decryption unit DU is adapted to decrypt incoming messages.  
         [0118]    The comparison unit is connected to the biometric data storage BDS, storing at least one pattern of biometric data.  
         [0119]    The comparison unit CU is adapted to perform a comparison between a prestored pattern of biometric data from the biometric data storage BDS and a decrypted pattern of biometric data received via the decryption unit DU and the input/output unit IO-U 1 . The comparison could for example be based on the comparison of feature vectors computed from patterns of biometric data.  
         [0120]    The processing unit PU is connected to the input/output unit IO-U 1 , the message encryption unit MEU, the decryption unit DU, the biometric data storage BDS and the comparison unit CU. The task of the processing unit PU is to process information and coordinate the units it is connected to.  
         [0121]    [0121]FIG. 6 depicts a hardware architecture of a client according to the invention. In the context of a UMTS telecommunication network the client could be a mobile station of a telecommunication network user. The client comprises an input/output unit IO-U 2 , a measurement device MD, an encryption unit EU, a feature extraction unit FEU, a hardware identification memory HWID, a user interface device UI and a central processing unit CPU.  
         [0122]    The measurement device MD can be for example a camera or a scanner capable of recording an image of a fingerprint of a user or a microphone for recording voice.  
         [0123]    The encryption unit EU can be any kind of unit capable of encrypting data.  
         [0124]    Optionally, the feature extraction unit FEU is intermediate between the measurement device MD and the encryption unit EU. The feature extraction unit FEU can be, for example, a unit extracting significant lines and cross-over points from an image of a fingerprint.  
         [0125]    The task of the input/output unit IO-U 2  is to connect the client to other entities. In the example of the mobile equipment of a UMTS user the input/output unit IO-U 2  is the radio interface of the mobile equipment.  
         [0126]    The measurement device MD is connected to the input/output unit IO-U 2  via the encryption unit EU.  
         [0127]    In the example case that the client is implemented as a mobile station of a UMTS subscriber, the user interface comprises a display and a keypad. In that example the hardware identification memory HWID can be implemented as a Wireless identification Module WIM storing an International Subscriber Identity IMSI.  
         [0128]    The central processing unit CPU is connected to the input/output unit IO-U 2 , the measurement device MD, the encryption unit EU, the feature extraction unit FEU, the hardware identification memory HWID, and the user interface device UI. The task of the central processing unit CPU is to process information and coordinate the units it is connected to.  
         [0129]    Each of the messages  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  31 ,  32 ,  33 ,  34 ,  35 ,  36 ,  37 ,  41 ,  42 ,  43 ,  44 , and  45  can be encrypted. Said encryption can be for example performed using a Secure Sockets Layer (SSL) protocol.