Abstract:
A portable data carrier comprises a memory with a biometric template which is intended to be compared with a biometric sample for identity check. The biometric template is divided into a private part which is adapted to be exclusively used in the portable data carrier and a public part which is adapted to be transferred to and used in an external processing unit. Moreover, a processing unit for use in biometric identity check is described. The processing unit is adapted to receive a biometric sample and a public part of a biometric template, compare the received public part of the template with the biometric sample, and when a comparison criterion has been satisfied, transfer at least part of the biometric sample to the portable data carrier for further comparison in the data carrier with a private part of the template. A method for recording a biometric template and a biometric identity check is also described.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a portable data carrier which comprises a biometric template which is intended to be compared with a biometric sample for identity check. The invention also relates to a processing unit for use in biometric checking of identity, a system for checking of identity, a method of producing a biometric template and a method for performing a biometric identity check.  
         BACKGROUND OF THE INVENTION  
         [0002]    The access to information, to a room or the like must in many cases be restricted to certain individuals. This is the case, for instance, when electronic money transactions occur via the Internet, when in a hospital the access to case records is to be limited, or when only certain individuals in a place of work are allowed to have access to certain information or certain rooms.  
           [0003]    To this end, use is often made of what is referred to as intelligent cards or smart cards. A smart card can be described as a card in the size of an account card which has a built-in processor or a signal processing means, a memory and a communication interface. Sensitive information is stored on all smart cards used in the above contexts. The sensitive information consists of one or more parts. A first part of the sensitive information is a so-called template which is stored on each smart card and can be described as reference information, stored in advance, about the user of the card. It is with this reference information that a comparison is made every time the card user wishes to verify his right to use the card. The template is further the only sensitive information that need be available on the smart card if it is intended for use as a pure “key card” and to generate a “yes” or “no”, for instance, for physical access to a room.  
           [0004]    Also so-called hardware tokens work essentially according to the same principle as smart cards. They are typically used in a computer as a key to “unlooked” the computer and give a user access to information. The difference compared with a smart card is more of a practical type since a hardware token can be directly inserted into the USB or serial port of a computer while a smart card must be placed in a special smart cart reader which is connected to the computer. For this reason, also the software on the hardware token differs somewhat from the software on smart cards, but their purpose is essentially the same.  
           [0005]    Smart cards that are not used as “key cards” but are used as more absolute information carriers also contain a second part containing sensitive information. The second part containing sensitive information consists of computer files which may contain data of the type which is mentioned by way of introduction and which only the card user may access. When the card user wants to verify that he has the right to access to the sensitive information stored in the computer files on the smart card, he places the card in a terminal and enters a PIN code (PIN=Personal Identification Number). The pin code is limited to 16 bytes and usually consists of four digits between zero and nine which are matched with the template stored on the card. If the pin code corresponds with the template, “the card is unlocked”, i.e. the user gains access to the computer files containing the sensitive information. This differs from the case where the card is used as a pure “key card” and only a “yes” or a “no” is generated in response to the matching with the template.  
           [0006]    Pin codes are presently used in many situations, and many people find it difficult to remember a number of different pin codes. Therefore, many people choose to use the same pin code in a number of different situations, thus deteriorating security. For this reason, and with a view to further increasing security, alternative solutions have been presented, in which a user instead identifies himself with the aid of biometric information. By biometric information is meant information which is body-related and individual-specific for the user and which may consist of, for instance, the pattern of the user&#39;s fingers, palm, iris, or some other information which is not related to appearance, such as the user&#39;s voice. A method in which a user identifies himself with the aid of biometric information according to prior art typically proceeds as follows:  
           [0007]    The user places his smart card in a terminal and one finger on a sensor which generates a digital image, i.e. a digital representation, of his finger. The digital image of the fingerprint proceeds to an external processor, for instance a personal computer, where it is preprocessed. In the preprocessing, the amount of information in the image is reduced so that, for instance, a binarized image or parts of a binarized image are generated. A corresponding preprocessed image has been stored on the card as a template. The external processor collects the template from the card and compares this with the preprocessed image of the finger. In case of correspondence, the external processor transmits a pin code to the card. This pin code acts as a key and gives access to the sensitive information stored in the memory of the card. If the template and the preprocessed image information do not correspond with each other, no pin code is transmitted and the user cannot access the computer files with the sensitive information on the card.  
           [0008]    Even if biometry is used so that the user will not need to use a pin code, a pin code is still transmitted at the last stage of the verification process since this pin code is necessary for the “unlocking” of specific files containing sensitive information on the smart card. Thus the pin code must be hardcoded either in the software for the application which communicates with the card, or in some hardware in the unit where the card is read and written. Consequently no significant increase of the security is achieved despite the use of biometry since there is still a risk that someone may access the computer files with sensitive information on the card by transmitting the pin code to the card.  
           [0009]    Also in the case where the only action of the smart card is to generate a yes or no, it is necessary to encrypt the information on the card to be able to guarantee that the yes/no that is transmitted is unique for each card or transmission. This causes the same problems as described above since the key for encryption must be stored somewhere.  
           [0010]    A further problem is that the template with which the matching occurs must be read from the card into the external processor in which the comparison with the user&#39;s biometric data takes place. In the first place this is a security risk, and in the second place there are directives issued by computer security authorities in certain countries which recommend that a biometric template should never leave the smart card.  
           [0011]    One solution to the above problems is presented in Swedish Patent No. 8101707-1 which discloses an account card type data carrier which is provided with verification equipment comprising a sensor on which a user places one of his fingers. The sensor records papillary line information from the user&#39;s finger and calculates an identification bit sequence which is compared with a previously stored reference bit sequence. If the bit sequences conform with each other, an acceptance signal is generated, which can activate an indication means or a connecting means which makes the data carrier useable.  
           [0012]    Although this solution eliminates the use of pin codes and lets the template remain on the card all the time, certain drawbacks still remain. For example, the card will be relatively expensive to make generally accessible to a large number of users since it contains a large number of components and must be specially made. Owing to the large number of components and the fact that all operations are effected on the card, also the probability increases that the service of the card will be interrupted. Furthermore it is difficult to protect the sensor on the card against external mechanical action.  
         SUMMARY OF THE INVENTION  
         [0013]    An object of the present invention therefore is to obviate, or at least alleviate, the above problems and to provide an alternative system for checking the identity of people requesting the tight to access to sensitive information.  
           [0014]    According to the invention this object is achieved by a portable data carrier which has the features defined in appended claim 1, preferred embodiments being stated in appended claims 2-8. The object is also achieved by a processing unit according to claims 9-15, a system according to claim 16 and a method according to claims 17-24.  
           [0015]    More specifically, the invention concerns a portable data carrier, comprising a communication means and a memory with a biometric template which is intended to be compared with a biometric sample for identity check. The biometric template is divided into a private part which is adapted to be exclusively used in the portable data carrier and a public part which is adapted to be transferred, with the aid of the communication means, to an external processing unit and be used in the same.  
           [0016]    By data carrier is meant a number of different units, such as smart cards, hardware tokens etc, which all have the feature in common that they have a communication means which can communicate with an external processing unit and a memory containing information. This information can exist either merely in the form of a “key” or both in the form of a key and in the form of “sensitive information” which a user may access by verifying by means of biometry his right to use the key. For the data carrier to be usable in as many situations as possible, it is important for it to be portable, i.e. that a user should be able to carry the data carrier in a simple way without needing any extra aids for this purpose.  
           [0017]    By the expressions biometric template and biometric sample are meant data that is unique for an individual. Examples of such data can be the pattern of the person&#39;s fingers, palm, iris, or the person&#39;s voice. The template relates to reference information which is stored on the data carrier and which is not changed after the original storage, whereas the sample relates to biometric data which must be presented by a person on each occasion of checking his or hers identity.  
           [0018]    The fact that the template is divided into a private and a public part means that only part of the template need be transferred to an external processing unit. This results in a quicker comparison with the biometric sample in the external unit since a smaller quantity of data is used. Moreover a possibility of utilizing different security levels for different applications is created since it is possible either to merely make a first comparison between the public part of the template and the biometric sample in the external processing unit or, in addition, to make a comparison in the data carrier between the private part of the template and the biometric sample. The utilization of an external processing unit also allows a safer comparison since more processing power is available compared with what can be achieved on a data carrier, and more complex comparison criteria can thus be used. Furthermore the comparison on the data carrier can be performed with less processing power, which makes it possible, for example, to use standard type smart cards.  
           [0019]    According to a preferred embodiment, the communication means is further adapted to transfer the public part of the template to the processing unit for comparison with the biometric sample and, when a comparison criterion has been satisfied, to receive at least part of the biometric sample for comparison with the private part of the template in the portable data carrier.  
           [0020]    This means that first a check of the biometric sample is made in the processing unit, and if this check satisfies a predetermined comparison criterion, one or more parts of the biometric sample are transferred to the data carrier for a final check in the same. By the final identity check of the right to access being made on the data carrier, no pin code need be generated in the processing unit and transferred to the data carrier. Instead one or more parts of the biometric sample are transferred, which is much more difficult to fake since it is much more complex than a common pin code. Security also increases still more since it is impossible for an ill-intentioned person to steel or copy the entire template from the processing unit since only part thereof leaves the data carrier to be used in the first comparison in the processing unit.  
           [0021]    In one more preferred embodiment of the invention, the biometric template and the biometric sample consist of digital representations of an individual-specific parameter. By a digital representation of an individual-specific parameter is meant a recording in digital form of a body-related characteristic which in some way is unique for an individual. Examples of this can be a digital image of the pattern on the individual&#39;s fingers, palm, iris, or a frequency spectrum of the individual&#39;s voice, or some other type of representation of a unique characteristic which is related to the individual&#39;s body. The advantage of using digital representations is that they can quickly and easily be recorded and easily be processed in various ways.  
           [0022]    The private and public parts of the biometric template each comprise preferably a plurality of private and, respectively, public partial areas of the digital representation of the individual-specific parameter. The term partial area is here used in a conventional sense and relates simply to a smaller part of the digital representation, such as a part of a digital image or a specific frequency range in a frequency spectrum of the individual&#39;s voice. By using partial areas, the total amount of information used in the comparison is decreased while at the same time security is maintained since it is possible to select partial areas containing particularly relevant information, such as relevant intersections between lines in a fingerprint. in a preferred embodiment of the portable data carrier, the number of private partial areas is greater than the number of public partial areas in the template. As a result, only one or a few areas need be transferred from the data carrier to the external processing unit. The comparison with the biometric sample in the external processing unit will therefore be quicker and at the same time security increases still more since a large part of the template never leaves the data carrier.  
           [0023]    For instance, there may be a single public partial area which is collected from the center of a fingerprint and a plurality, for instance four to eight, private partial areas which are placed in predetermined positions at a distance from the public partial area.  
           [0024]    In an alternative embodiment, at least one private partial area is located in immediate connection with a public partial area in the biometric template. This makes it easy to determine which partial areas of the biometric sample are to be transferred to the data carrier after the check in the processing unit. Moreover, this partial area of the biometric sample will have been affected in the same manner (for example, the distance between the lines in a fingerprint varies with the force used by the individual when applying his finger to the sensor) as the partial area which was compared with the public part of the template, which results in quicker and safer identification.  
           [0025]    Preferably, the individual-specific parameter is a fingerprint. This makes a simple recording procedure possible, in which conventional sensors can be used and the individual can easily provide the biometric sample.  
           [0026]    The portable data carrier is preferably also a smart card. These cards can be of different standard types, such as Java or MULTOS cards, which are simple and inexpensive types of data carrier which can easily be adapted to different applications and which are easy for a user to carry. A standard type smart card which contains data about a certain user can thus be used in a plurality of situations since it is precisely standardized and since the operating system on the card handles the files in such manner that the handling of the files is independent of the application in which the card is used.  
           [0027]    According to a second aspect, the invention relates to a processing unit for use in biometric checking of identity, comprising a processor and a communication means. The communication means of the processing unit is adapted to receive a biometric sample and a public part of a biometric template, the processor is adapted to compare the received public part of the template with the biometric sample and the communication means is further adapted to transfer, when a comparison criterion has been satisfied, at least part of the biometric sample to the portable data carrier for further comparison on the data carrier.  
           [0028]    The processing unit can be available in a number of different embodiments, but a common feature is that they must comprise a processor and communication means which can transfer data in digital form to and from the data carrier. The expressions biometric template and biometric sample have the same meaning as stated above, where also the advantages of the processing unit have been discussed in detail.  
           [0029]    The comparison criterion used in the processing unit to decide whether parts of the biometric sample are to be sent to the data carrier may vary between different applications, depending on which security level is desirable, and can easily be entered in the processing unit by a person skilled in the art who is responsible for the current security system.  
           [0030]    The public part of the template comprises preferably a plurality of public partial areas which are adapted to be compared with a plurality of sample partial areas having essentially corresponding positions in the biometric sample.  
           [0031]    In a preferred embodiment, said at least part of the biometric sample which the communication means is adapted to transfer to the portable data carrier is essentially separated from the sample partial areas of the biometric sample which the processor is adapted to compare with the public partial areas of the template.  
           [0032]    In one more preferred embodiment, the processing unit is further adapted to preprocess the biometric sample before the comparison with the public part of the template. A purpose of this preprocessing is to “translate” the biometric sample into the same form as the public and private parts of the template. One more purpose is to reduce the quantity of data in the original biometric sample so that a safe comparison can still be made although with a smaller quantity of information, which makes the comparison with the template quicker. The type of preprocessing that is used may vary depending on the format in which the biometric sample originally exists, but the general purposes are always the same as those mentioned above. A consequence of the preprocessing of the biometric sample in the processing unit is that the data carrier can in most cases consist of inexpensive smart cards or standard type hardware tokens, such as Jave cards or Multos cards, and need not be specially made or comprise a large amount of components, which is the case in the prior-art technique.  
           [0033]    In another preferred embodiment, the processing unit further comprises a sensor for recording the biometric sample. This means that no extra equipment need be connected to the processing unit and the recording and preprocessing can thus be integrated so that the procedure as from the recording of the user&#39;s biometric sample up to and including the transfer to the portable data carrier will be quick. Also security increases since the biometric sample need not be transferred between a special recording unit and the processing unit. The sensor can also be better protected against mechanical action compared with the case where it is positioned on the actual data carrier.  
           [0034]    The biometric template and the biometric sample are preferably digital representations of an individual-specific parameter, and in the currently most preferred embodiment, the biometric sample is a fingerprint. The term individual-specific parameter and the advantages of using fingerprints have been discussed in detail above in connection with the portable data carrier.  
           [0035]    According to a third aspect, the invention relates to a system for checking identity, comprising a portable data carrier and a processing unit according to one of the embodiments described above. The advantages of a system of this type will also be evident from the discussion above.  
           [0036]    According to a fourth aspect of the invention, it relates to a method of producing a biometric template, comprising the steps of recording a digital representation of a biometric sample which represents an individual-specific parameter; selecting in the digital representation at least one public part; selecting in the digital representation at least one private part; storing the selected public and private parts in a memory in a portable data carrier as a public and a private part of a biometric template, the private part being adapted to be exclusively used in the portable data carrier and the public part being adapted to be used outside the portable data carrier.  
           [0037]    When producing the template, a recording of a biometric sample thus is made according to a prior-art method, in which the result is a digital representation, such as a digital image of the current biometric sample. In this sample, private and public parts are then selected. The selection of private and public parts means that the quantity of data that need be stored on the data carrier decreases to a considerable extent, and the advantages arising in consequence of this have been quite thoroughly discussed above. After the areas have been selected, they are transferred to the data carrier and stored permanently in the memory thereof.  
           [0038]    According to a preferred embodiment of the above method, the public and the private part each consist of at least one partial area of the digital representation which is selected according to a predetermined public and, respectively, private selection criterion.  
           [0039]    The selection criterion can vary according to how safe the identification is to be made. For example, the public and the private parts can either be selected in the same way for all individuals, or they can be selected in a unique way for each individual, where the areas which are of greatest interest from the viewpoint of identification are selected. However, the public part or parts are advantageously selected in such manner that they will be easy to find in the comparison with the biometric sample. Consequently, a quick identification can be carried out in the processing unit. The private parts, however, can be selected according to other criteria since their position in the biometric sample can be related to the position of the public part and a quick identification can therefore still be achieved.  
           [0040]    According to one more preferred embodiment of the method of producing a template, it further comprises the step of preprocessing the digital representation of the public partial area and the private partial area before storage in the memory of the portable data carrier.  
           [0041]    The advantages of preprocessing will be evident from the discussion above in connection with the processing unit.  
           [0042]    Preferably, the digital representation consists of a digital image and the individual-specific parameter consists of a fingerprint. A large number of image-processing algorithms of different types are available and fingerprints are easy to collect and process, which results in a simple as well as flexible way of making an identity check of an individual.  
           [0043]    According to a fifth aspect of the invention, it relates to a method of performing a biometric identity check, comprising the steps of recording a biometric sample which represents an individual-specific parameter; comparing in a first unit a public part of a biometric template with the biometric sample to find out whether a first predetermined comparison criterion is satisfied; selecting, if the first comparison criterion is satisfied, a private part of the biometric sample according to a predetermined private selection criterion and transferring the private part to a second unit; comparing in the second unit the private part of the biometric sample with a private template stored in the second unit to find out whether a second predetermined comparison criterion is satisfied.  
           [0044]    Preferred embodiments of this method are discussed in claims 23 and 24, and the advantages achieved are essentially the same as those mentioned in the above discussions about the data carrier, the processing unit and the method of recording a template with a public and a private part. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]    The invention will now be described in more detail by way of an embodiment with reference to the accompanying schematic drawings.  
         [0046]    [0046]FIG. 1 is a schematic drawing illustrating a portable data carrier and a processing unit according to the invention.  
         [0047]    [0047]FIG. 2 is a block diagram illustrating a method according to the invention of producing a biometric template with a private and a public part and store this on a portable data carrier.  
         [0048]    [0048]FIG. 3 is a block diagram illustrating a method according to the invention of performing a biometric identity check.  
         [0049]    [0049]FIG. 4 shows two different methods of selecting private and public parts of a biometric sample for storage in the form of a template on a portable data carrier. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0050]    [0050]FIG. 1 is a schematic view of a system according to the invention, which consists of a data carrier  1  in the form of a smart card and a processing unit  2 , which in this case is a computer. The smart card  1  is an ordinary standard type card, for instance a Java or MULTOS card, and has a communication means  3  which is adapted to communicate with a communication means  4  in the computer  2 . The smart card  1  further has a processor  5  and a memory  6 . The memory  6  contains sensitive information on the one hand in the form of computer files to which the person using the system wishes to gain access and, on the other hand, in form of a biometric template. This template has a private and a public part each consisting of a preprocessed digital representation in the form of a digital image. How the template is generated will be described below in connection with FIG. 2. In addition to the sensitive information and the template, the memory  6  also contains software which the processor  5  uses to compare the preprocessed image of the user&#39;s biometric sample, which has been transferred from the computer  2  to the smart card  1  via the communication circuits  3  and  4  respectively, with the template.  
         [0051]    The computer  2  comprises a processor  7 , which is used in the preprocessing of the user&#39;s biometric sample and in the comparison between this and the public part of the template. The biometric sample is recorded by means of a sensor  8 , which in this embodiment consists of a capacitive sensor. However, also other known types of sensors can be used that can record fingerprints, such as heat sensors, or optical sensors. The sensor  8  is connected to the processor  7  and to a memory  10 , in which software is stored for the preprocessing of the biometric sample that the processor  7  carries out. The memory  10  also comprises software which controls how the comparison between the preprocessed biometric sample and the public part of the biometric template is to be carried out, and which comparison criteria apply and when the communication circuits  4  are to collect the public part of the template from the memory  6  of the smart card  1 , and transfer part of the biometric sample from the computer  2  to the smart card  1 . The computer  2  also comprises circuits  11  for external communication with other units, such as additional sensors or information-carrying units. The communication between the different units in the computer  2  and on the smart card  1 , respectively, occurs via a data bus (not shown).  
         [0052]    For a comparison of the biometric sample and the public part of the template to be made in the processing unit  2  and for a comparison of part of the biometric sample and the private part of the template to be made on the portable data carrier  1 , it is necessary to produce a template which has a private and a public part with which the user&#39;s biometric sample can be compared each time an identity check is to be made. A description of how this template is produced follows below.  
         [0053]    [0053]FIG. 2 is a block diagram of a method according to the invention for producing a biometric template with a private and a public part and storing this on a smart card  1 . In step  20 , an image of the user&#39;s finger is recorded by means of the sensor  8  in the computer  2 . The result of the recording is a digital image in gray scale which represents the user&#39;s fingerprint. This digital image must first be preprocessed for a template with a public and a private part to be generated. The preprocessing can be carried out in many ways, one of which will be described briefly below.  
         [0054]    First, a check of the image quality of the fingerprint is carried out. It is checked, among other things, whether the user has applied his finger with sufficient pressure on the sensor  8  and so that any moisture on the user&#39;s finger has not made it impossible for the sensor  8  to distinguish between “ridges” and “valleys” on the finger. If the quality of the image is insufficient, the user is requested to correct the deficiencies in a suitable manner.  
         [0055]    When a digital image in gray scale of sufficient quality has been recorded by the sensor  8 , a binarization of the image occurs. The binarization implies that the pixels of the image are compared with a gray scale threshold value. The pixels which have a value smaller than the gray scale threshold value are converted to white and those having a value greater than the gray scale threshold value are converted to black. The gray scale threshold value can be the same for the entire image or vary between different parts of the image. The binarization algorithm can also be refined, so that the pixels are compared with the surroundings, so as to prevent, for example, individual pixels from being white if all the surrounding pixels are black. This adaptation is easily carried out by a person skilled in the art.  
         [0056]    After the binarization, at least one area of the image is selected in step  21  to be stored in the form of a public part of a template. The selection of areas for the public template can easily be made by a person skilled in the art. Some examples of how public areas can be selected, however, are shown in FIG. 4, where areas A-C in the upper part are public areas and areas  101 ,  201 ,  301  etc. is in the lower part of the Figure are public areas.  
         [0057]    When the public area or areas have been selected, at least one area is selected in step  22  to be stored in the form of a private part of a template on the smart card  1 . In FIG. 4 the private areas consist in the upper part of the Figure of areas D-J and in the lower part of the Figure of areas  102 ,  202 ,  302  etc. The private areas are always selected so that they are located in a predetermined relationship with the public areas. The number of public and private areas varies according to the desired security level, but for most applications eight areas, or fewer, are a good compromise between security and quickness in a matching situation. The size of the selected public and private areas in the template is in this embodiment 48×48 pixels, but can easily be adjusted by a person skilled in the art according to the prevailing requirements. The size and position of the various areas are selected so as to comprise as much individual-specific information as possible. For instance, areas with curved lines are of greater interest than areas with straight parallel lines.  
         [0058]    In step  23 , the public and the private part of the template are then transferred from the computer  2  via the communication circuits  3 ,  4  to the memory  6  of the smart card  1 . When the template has been transferred, additional sensitive information can also be transferred from the computer  2  and stored in the memory  6  of the smart card  1 , if desired. The recording of a template for the card owner is made only once. The other sensitive information can, however, be replaced when necessary.  
         [0059]    [0059]FIG. 3 shows a method according to the invention for performing a biometric identity check by means of the smart card  1  and the processing unit  2 . A person whose identity is to be checked first places his smart card  1  in a card reader either directly in the computer  2  or in a separate card reader communicating with the computer  2  via the external communication circuits  11  of the computer  2 . He then places his finger on the sensor  8  and a digital image is recorded in step  30  in the same way as described above. The image is preprocessed in the computer  2  in the same way as in the recording of the template, except that no partial areas are selected, so that otherwise it has the same format as the template stored on the smart card  1 . Subsequently, the preprocessing unit  2  receives the public part of the template which is stored on the smart card  1  via the communication circuits  3 ,  4 .  
         [0060]    In step  31 , the public part of the template is matched or compared with the biometric sample, i.e. the user&#39;s preprocessed fingerprint. In the matching, the public part of the template “sweeps” over the preprocessed image and in every position a comparison is carried out pixel by pixel. If a pixel in the template corresponds with the pixel in the preprocessed image of the fingerprint, a given value, for example 1, is added to a sum. If the pixels do not correspond, the sum is not increased. When the public part of the template has swept over the entire preprocessed image, a position is obtained where the public part of the template best overlaps a corresponding area of the preprocessed image. The public part of the template is rotated also in relation to the preprocessed image to find out whether a better match can be obtained.  
         [0061]    When the translation and the rotation have been made and the best matching position for the fingerprint and the public part of the template has been found, the obtained matching value is compared in step  32  with a predetermined first comparison criterion, which in this case is a reference sum. If the matching value is smaller than the reference sum, the identity check is considered to have failed, step  33 , but if the matching value is equal to or greater than the reference sum, the process proceeds in step  34 .  
         [0062]    In step  34 , one or more private parts are selected from the fingerprint by the processing unit  2  according to the same criteria as used in the recording of the template. The orientation of the biometric sample is already established since it is known how the biometric sample is oriented relative to the public part of the template. The private areas can therefore easily be selected to correspond to the private template. The private areas selected should, however, be somewhat greater than corresponding areas in the private part of the template to compensate for deformations of the fingerprint when applying the user&#39;s finger to the sensor. These selected private areas are then transmitted via the communication circuits  3 ,  4  to the smart card  1 . The areas can be transmitted in a predetermined sequence so that the processor on the smart card knows which area is which. As a further alternative, coordinates for the positioning of the private areas can be transmitted as well.  
         [0063]    In step  35 , the transmitted private areas are compared with the private part of the template by the processor  5  on the smart card  1 . This matching is less time consuming since an approximate position of the private partial areas is already known. When the pixels in the transferred private partial areas have been compared with the private part of the template, a total matching value between 0% (i.e. no match at all) and 100% (i.e. complete match) is obtained. This matching value consists of a second comparison criterion and is compared with a predetermined threshold value, step  36 . If the matching value is equal to or greater than the threshold value, the identity check is considered successful, step  37 , and the user gains access to the sensitive information stored on the card or gains access to a room etc. depending on the application in which the card is used. If the matching value is lower than the threshold value, the identity check is considered to have failed, step  33 , and the user is refused access to the sensitive information. A more comprehensive description of how partial areas in a fingerprint can be selected and how a template area is compared with a biometric sample area is to be found in Applicant&#39;s International Patent Application No. PCT/SE99/00553.  
         [0064]    Although a special embodiment of the invention has been described above, it is obvious to those skilled in the art that many alternatives, modifications and variations are feasible in the light of the above description. For example, the areas of the image that are selected for the match can be selected on the basis of completely different criteria than those described above. Completely different types of biometric data can also be used, such as the user&#39;s voice and a digital representation thereof in the form of a frequency spectrum, or the user&#39;s iris. Therefore the invention is considered to comprise all such alternatives, modifications and variations that are within the scope of the appended claims.