WO2001071474A1

WO2001071474A1 - Signature checking system

Info

Publication number: WO2001071474A1
Application number: PCT/SE2001/000593
Authority: WO
Inventors: Sven Olof Karlsson
Original assignee: Anoto Ab
Priority date: 2000-03-21
Filing date: 2001-03-21
Publication date: 2001-09-27
Also published as: AU2001239657A1; SE0000943L; SE518820C2; SE0000943D0; EP1269301A1

Abstract

A system for analyzing a user's signature. The system comprises a user unit (1) and a checking arrangement (2). The user unit (1) is arranged to record a signature when the user writes with the user unit (1), and to send the signature to the checking arrangement (2). The checking arrangement (2) is arranged to receive the signature. The ckecking arrangement (2) is also arranged to build a signature model based on the signature, to make a check of the uniqueness of the signature model and, after the check, to deliver a signal. The signal indicates the uniqueness of the signature model.

Description

SIGNATURE CHECKING SYSTEM

Technical Field

The present invention relates to a system for analysing the signature of a user, the system comprising a user unit and a checking arrangement, the user unit being arranged to record a signature which the user writes with the user unit, and to send the signature to the checking arrangement which is arranged to receive the signature. The invention also relates to a checking arrangement for analysing a user's signature which is written with a user unit, the checking arrangement being arranged to receive the signature, and a method for analysing a signature. Background of the Invention

The signature has long been used for increasing security when using different types of payment systems. For example, the signature is used on checks, with card payments and giro payments as an additional insurance that a paying person or payment receiving person is really the one he claims to be. The signature can be written with a normal pen or with an electronic pen. In the case of electronic pens, it is possible to increase the number of parameters which describe the signature. It is not only possible to calculate the same parameters as with a normally written signature such as, for example, the absolute size and slope of the letters, but it is also possible to calculate, for example, how hard the electronic pen is pressing on the base and the speed with which the signature is written. This can be read in the article "Optimisation issues in dynamic and static signatures verification" in Handwriting Analysing and Registration (ref. No. 1998/440), IEE Third European Workshop, 1998, page 5/1-5/6, written by C . C .^' Allgrove and M.C. Fairhurst, which also describes a method with which a verification database can be built up. In the article, a verification system is described which comprises a verification database in which reference models for a number of signatures are stored. The signature of a person varies a little every time it is written and the reference model takes account of these variations. When a reference model is built up, the user writes a signature a number of times and this provides a range within which the signature of the user lies. To improve the reference model, the signature or signatures which differs a lot from the user's other signatures written can be filtered out. Summary of the Invention

It is an object of the invention to provide a system which increases security when using electronic signatures.

This object is achieved by means of a system for analysing a user's signature according to claim 1, a checking arrangement according to claim 13 and a method according to claim 19.

More specifically, the invention provides, according to a first aspect, a system for analysing a user's signature, the system comprising a user unit and a checking arrangement, the user unit being arranged to record a signature when the user is writing with the user unit, and to send the signature to the checking arrangement which is arranged to receive the signature, the checking arrangement being further arranged to build a signature model based on the signature, and to make a check of the uniqueness of the signature model and, after the check, to deliver a signal which indicates the uniqueness of the signature model.

The invention is based on the concept of providing a user with the possibility of checking how unique his or her signature is. By a unique signature is meant not only that the signature is unlike other signatures but also, for example, that it contains characteristics, which bring about better machine recognition of the signature. The signature is normally the user's signature but can also be a symbol or any type of sign. The advantage of the user being able to check the uniqueness in his or her signature is thus that the user can obtain an indication of how good the signature is, i.e., for example, how difficult it is to forge, to mistake for another signature or how simple it is to process in a machine-recognition program.

The user unit or part of the user unit can be constructed as a pen with which the user writes the signature and can be, for example, a digital pen. The user unit records the signature and sends a representation of the signature on to the checking arrangement.

The signature is received by the checking arrangement. When the signature is received, one or more parameters can be determined. These parameters can be, for example, the length of the signature, the slope of the letters and/or the number of bends in the signature. A bend can be defined as a relatively large change in the direction of the signature. The parameters can then be compared with predetermined minimum levels within which they should lie for the signature to be considered to meet certain uniqueness requirements. In a very simple case, the signature model consists of a signature and the above-mentioned check can be the uniqueness check itself. In a very simple example of a uniqueness check, the check is done on only one parameter, for example the number of bends in the signature. If, in this case, the signature only consists of a line, which means that the number of bends is zero, and the limit level for the number of bends is determined to be greater than or equal to 10 for the signature to be determined to be unique, the checking arrangement will determine that the signature is not unique. Apart from comparing the parameter with a predetermined limit level, it can also be compared with one or more parameters of signatures which were stored earlier. Taking the former case where the parameter is the number of bends, it can have been determined that, for a signature to be considered as unique, it must differ by two steps in the number of bends from signatures stored earlier .

The checking unit can be arranged in for example a verification system in which several signature models is stored. The checking unit is then arranged to check the uniqueness of the received signature model by comparing with all stored signature models. The signature model can- only be determined to be unique if it distinguishes to a certain degree from all the stored signature models.

Preferably, the comparison is carried out partly with a predetermined limit level and partly with signatures stored earlier. This is certainly a simplified explanation of the check of the uniqueness of the signature. Preferably, a large number of different parameters is used for making the check of the uniqueness of the signature. The signature model can be built up from a number of received signatures from the same user but can also be made up of only the received signature which was the simple case mentioned above. If the signature model is built up of a number of signatures, the above- mentioned minimum requirements check can be carried out for each signature which then builds up the signature model. If the minimum requirements check is carried out, the signature model is built up of signatures which at least meet certain criteria. The checking arrangement then carries out a check on how unique the signature model is. To carry out the check and evaluate the different parameters, different classification methods can be used. Normally, a classifier which can be, for example, a neural network, is used in these methods. A classifier can be "trained" by feeding in parameters of a signature and comparing the response value which comes out with the required result. If the response value is not the one required, the classifier is adjus.ted and the parameters are fed in again and the response value is compared with the one required. This is continued until the required result is obtained. When a uniqueness check is to be carried out on a signature, which signature does not need to be stored in the neural network, its parameters can be fed into the classifier. The response value output from the classifier can be a measure of uniqueness .

The classifier can also provide an indication of how close a signature model input is to a signature model stored earlier.

If the signature model comprises more than one signature, the classification is normally done after each received signature and the signature model can be built up in this manner.

When the check of the uniqueness of the signature model is completed, the checking arrangement sends a signal to the user unit in order to inform the user about how unique his signature is. If the uniqueness is not adequate, the checking arrangement can send along information about what can be changed in the signature to make it unique. The signal may also be only an enabling signal which indicates that the signature is unique, or a signal which only indicates that the signature is not sufficiently unique.

In another embodiment of the system, the signature model is the signature.

Sometimes it may be desirable to get a quick check of the uniqueness of the signature and the user then only writes his signature once. The signature model is then the signature, and the checking arrangement is then arranged tc check the uniqueness of this single signature.

In one embodiment of the system, the checking arrangement is arranged to build up the signature model from a number of signatures received from the same user.

The signature model is advantageously built up from a number of signatures written by the same user. The advantage of the signature model is that it takes into account variations in the signature of the same user. A user often has small variations between different writings of the signature. The signature model can be improved further by eliminating, for example, the signature which differs the most from the other ones.

In another embodiment of the system, the checking arrangement is arranged to calculate, in the check of the uniqueness of the signature model, at least one parameter which is characteristic of the signature model and to make a check of said at least one parameter.

There are many parameters which may be interesting to examine in the signature model for checking its uniqueness. As mentioned above, one parameter may be enough for making a uniqueness check, but a plurality of parameters are advantageously used since the uniqueness check of the signature becomes more secure. Access to a large number of parameters provides better classification. The uniqueness check does not need to be made directly on the parameter but the parameter can be fed directly to a classifier. The classifier provides a response value which provides a measure of uniqueness and on which the uniqueness check can be carried out.

A parameter which can be used for the uniqueness check is, for example, the extent of the signature. The extent can be calculated, for example, as a height/length ratio or else an absolute length. Other parameters can be, for example, the number of bends, the derivative of movement in the x-direction and y-direction, the absolute size of the signature, crossings, curves, line ends and the pressure with which the signature is written. Further parameters can be the slope of letters and words.

In one embodiment of the system according to the invention, the checking arrangement is arranged to check, in the check of said at least one parameter, that the said at least one parameter is above a predetermined uniqueness limit level.

The uniqueness limit level is set at a level at which, if said at least one parameter of the signature model is below this level, the signature model is deter- mined not to be unique. If, on the other hand, it exceeds or is at this level, the signature is considered to be unique. Certainly, this level can be defined in such a manner that, if the level is below the predetermined uniqueness limit level, the signature is determined to be unique. It can be defined in the system how the checking arrangement processes the comparison of said at least one parameter with the uniqueness limit level. An advantage of using this uniqueness limit level is that it is possible to obtain an indication of how unique the user's signature is on the basis of how much the signature model differs from the uniqueness limit level.

The signal from the checking arrangement to the user unit can comprise information whether the signature model is over, under or on the limit of the uniqueness limit level. The signal can also comprise information about how much it deviates from the uniqueness limit level. The advantage of this is that the user obtains information on how secure his or her signature is and, based on this, the user obtains, for example, an indication of what the signature can be used for. If the signature has a high degree of uniqueness, the user can use it, for example, in a payment system.

The uniqueness limit level of the checking arrangement can be adjusted depending on the application in which the user's signature is intended to be used. The system can be arranged in such a manner that the user unit sends information about the application together with the signature to the checking arrangement. The checking arrangement then uses the uniqueness limit level belonging to this application. If a classifier is used, the uniqueness limit level can be a response limit level. If the response limit level from the classifier is increased, the security level can be increased.. The output value from the classifier can be compared with the response limit level for determining if the signature is unique . In another embodiment of the system according to the invention, said signal comprises information about what the user has to change in the signature for said at least one parameter to end up above the uniqueness limit level.

The advantage of the user obtaining information about what to change in the signature to render it unique is that the user can obtain a unique signature in a quick and simple manner. The user does not need to randomly change different parts of the signature until it is determined to be unique but can obtain direct information on what to change .

In one embodiment of the system, the checking arrangement is also arranged to classify the signature.

The checking arrangement advantageously classifies each received signature. If the signature model is to comprise more than one signature, each signature is classified to build up the signature model.

To facilitate the classification of the signature, a number of parameters are advantageously used. The advantage of classifying is that it becomes quicker to check the uniqueness of the signature. As mentioned above, there are different methods for carrying out a classification.

In yet another embodiment of the system, the checking arrangement is arranged to compare, in the check of the uniqueness of the signature model, the signature model with other signatures..

In order for the signature to be unique also in relation to signatures stored earlier, the signature model is compared with signature models stored earlier so that the stored signature models are not too similar to each other. The signal from the checking arrangement to the user unit can provide information for the user about what the user needs to change in his signature so that it is not too similar to an earlier signature written by another person. It depends on the application of the signature how much two signatures written should differ. This comparison is carried out advantageously in combination with the check that the signature model is above a predetermined uniqueness limit level.

In one embodiment of the system, the signature is recorded as a sequence of coordinates which describes the displacement of the user unit when the user writes his signature with the user unit.

By describing the signature as a sequence of coordinates, it is possible to calculate different parameters of the signature in a simple manner.

In another embodiment, the system comprises a base which is provided with a position-coding pattern which enables the coordinates to be calculated and from which the user unit is arranged to record the sequence of coordinates .

The user unit records the pattern and suitably calculates its corresponding pairs of coordinates. The pairs of coordinates can be stored in a memory in the user unit. The user unit can also be arranged to analyse stored pairs of coordinates and to convert these to a train of polygons which constitutes a description of how the pen has been displaced over a surface which is provided with the position-coding pattern, the displacement being the user's signature. The train of polygons can then be transferred to the checking arrangement for uniqueness check. The time when different pairs of coordinates were recorded can also be recorded to obtain an additional parameter.

In one embodiment of the system, the user unit comprises an optical sensor and image-processing means for recording the signature.

The optical sensor captures images and image-processing means process the images, which includes determination of the coordinates from the content of the images, in which case the content can be the above-mentioned position-coding pattern. In one embodiment of the system, the checking arrangement is arranged in a verification database.

The checking arrangement is advantageously arranged in a verification database in which a plurality of different signatures can be stored in the form of signature models. If the signature model is already stored in the memory, the verification database can also confirm the correctness of the signature. This can be done, for example, by the user unit sending along a user identity to the verification database. The verification database then knows with which signature a comparison is to be made. The signal which is delivered to the user unit can then inform the user about how similar the signature is to the stored one. Perhaps, the user's signature has changed.

According to a second aspect, the invention also relates to a checking arrangement for analysing a user's signature which is written with a user unit, the checking arrangement being arranged to receive the signature, the checking arrangement being further arranged to build a signature model based on the signature, to make a check of the uniqueness of the signature model and to deliver a signal, which indicates the uniqueness of the signature model .

According to a third aspect, the invention relates to a method for analysing a signature comprising the steps of recording a signature with the aid of a user unit, sending on a representation of the signature to a checking arrangement, building up a signature model in the checking arrangement, making a check of the uniqueness of the signature model in the checking arrangement and, after the check, delivering a signal, which indicates the uniqueness of the signature model.

According to a fourth aspect the invention relates to a method for analysing a user's signature, which is written by a user unit comprising the steps of receiving the signature, building a signature model based on the signature, making a check of the uniqueness of the signature model, and delivering a signal, which indicates the uniqueness of the signature model.

The check of the uniqueness can be made by comparing the received signature model with already stored signature models. These signature models can be stored and used in a verification system, which verify users by their signatures. The received signature model must distinguish from all stored signatures to be considered unique.

According to a fifth aspect the invention relates to a computer program product directly loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of above mentioned method when said product is run on a computer.

The advantages of the checking arrangement, the methods and the computer product are apparent from the above description. The features discussed with respect to the system also apply in suitable parts to the checking arrangement and the methods . Brief Description of the Drawings

The invention will be described in greater detail in the text which follows, referring to the accompanying drawings .

Fig. 1 is a schematic view of an embodiment of the system.

Fig. 2 shows an example of a user unit.

Fig. 3 shows an example of a handwritten signature.

Fig. 4 illustrates a flow chart describing a method according to the invention. Description of a Preferred Embodiment

Fig. 1 shows an embodiment of the system according to the invention. The system comprises a number of user units 1 and a checking arrangement integrated with a verification database 2. For the sake of simplicity, Fig. 1 only shows one user unit. The verification database 2 and the user unit 1 communicate via a corrrouter network 3. The user unit 1 is equipped with a network access unit 4 which, in this example, can communicate wirelessly with the verification database 2. The network access unit is in this case integrated with the user unit but, as an alternative, can be a mobile telephone, a computer or some other suitable unit which has an interface to a network, for example the Internet or a local company network. Writing Base

Fig. 1 shows an example of a writing base 5 which is like a normal magnetic or credit card in size and material. The writing base 5 has a writing field 6 which may have a size of 10 mm times 200 mm and can be provided with coordinates which can be read by the digital pen 1. The coordinates can be specified in explicit or coded form. In this example, the writing base 5 is provided with a position-coding pattern 7. The pattern 7 is shown schematically as a number of dots on a part of the writing base 5.

The writing field 6 is intended for handwritten information which, in this case, is the user's signature. The writing base 5 can be made of such material that the signature can be erased after it has been written. As an alternative, the combination of pen and writing base can be such that no dye is deposited on the writing base when the user writes the signature.

The position-coding pattern 7 can be of such a type as is shown in US 5,852,434 where each position is coded by a specific symbol.

However, the position-coding pattern 7 is advantageously of the type shown in Applicant's above-mentioned applications WO 00/73983 and PCT/SE00/1667 , where each position is coded by a plurality of symbols and each symbol contributes to the coding of a plurality of positions. The position-coding pattern 7 is built up by a small number of types of symbols. One example is shown in WO 00/73983, where a relatively large dot represents a "one" and a smaller dot represents a "zero". Another example is shown in PCT/SE00/1667 , where four different displacements of a dot in relation to a raster point code four different values. Moreover, reference is made to WO 01/16691, the content of which is included in the present specification by reference. User Unit

Fig. 2 shows an example of a user unit which, in this case, consists of a digital pen 1. It comprises a casing 11 which is approximately formed like a pen. In a short side of the casing there is an opening 12. The short side is intended to bear against or be held at a short distance from the surface on which the position determination is to be carried out.

The casing mainly accommodates an optical part, an electronic part and a power supply.

The optical part comprises at least one light- emitting diode 13 for illuminating the surface which is to be imaged and a light-sensitive area sensor 14, for example a CCD or CMOS sensor for recording a two-dimensional image. The arrangement may also contain a lens system.

The power supply for the user unit is obtained from a battery 15 which is mounted in a separate compartment in the casing.

The electronic part comprises a processor 16 which is programmed for reading an image from the sensor 14, identifying symbols in the image, determining which two coordinates are coded by the symbols and storing these coordinates in its memory. The processor 16 is also programmed for analysing stored pairs of coordinates and converting them to a train of polygons which constitutes a description of how the pen has been displaced over a surface which is provided with the position-coding pattern, which displacement can be, for example, the user's signature. Finally, the processor is programmed for generating a message which contains the train of polygons and sending this information to the verification database 2 via the transceiver 19 and the network access unit 4.

The digital pen 1 also comprises a pen point 17, with the aid of which the user can write normal dye-based writing which, at the same time, is recorded by the pen 1 with the aid of the position-coding pattern. The pen point 17 is retractable and extendable so that the user can control whether it is to be used or not.

The digital pen 1 also comprises buttons 18, with the aid of which the unit is activated and controlled. It also has a transceiver 19 for wireless communication, e.g. by means of IR light or radiowaves, with external units . Check of the Uniqueness of a Signature

Fig. 1 shows an embodiment of the invention in which the user unit is a digital pen 1 and the checking arrangement is arranged in a verification database 2. Fig 4 illustrates a flow chart for the method. The verification database 2 can serve a plurality of digital pens 1. The digital pen 1 is arranged to transfer information generated by the user to the verification database 2. In this case, the information is transferred via a network access unit 4 which is integrated with the digital pen 1. The verification database is implemented in a computer which is configured with one or more processors, memories of different types, peripheral units and with new software for carrying out the functions described here. It also has information stored in a memory for being able to manage these functions.

In the memory of the verification database 2, signature models written earlier and different uniqueness limit levels are stored. A signature model received in the verification database is compared with the uniqueness limit levels for checking the uniqueness of the signature model. The uniqueness limit levels can be linked, for example, to different applications which make different demands on security. It may be possible for a user to select on the user unit the application and/or the security level at which the signature is to lie. This information can be transferred to the verification database together with the signature. The verification database 2 then uses the limit level which is associated with the specified application.

When a user wishes to add her signature in an verification database she must first investigate if her signature is unique. She therefore writes her signature with the digital pen 1 on a writing base 5. The pen 1 records 100 the signature electronically as a sequence of coordinates. It also records the time instant for each coordinate. Thus, it is possible to calculate the speed and acceleration by taking the derivative of the position coordinate over time. Moreover, it is possible to calculate the tilt of the pen or angle and rotation to the base. It is also possible to equip the digital pen 1 with a pressure sensor which senses the pressure with which the signature is written. The pressure can be determined at different times. The sequence of coordinates and the times at which the pen passes these coordinates are sent 110 to the verification database 2 via the network access unit 4 and over the computer network 3. The user writes her signature a number of times and the user unit transfers this information. The signature must be written a number of times since there are almost always certain variations between different writings of the signature, and to compensate for these, a signature model is built up 120 which sets up frames for how much the signature can vary in order to be considered as belonging to the same user. The verification database receives and classifies each signature. When each signature is received, a minimum requirements check can be carried out, that investigates that the signature fulfils at least some of the requirements of the uniqueness. For example, the length of the signature can be checked and if it is below a predetermined minimum level, a signal can be sent to the user unit which tells the user that the signature cannot be accepted, because it is too long or too short and, thus, insufficiently unique. The signal can also contain information about why the signature cannot be accepted. Each signature is classified on the basis, for example, of the extent of the signature. The extent can be calculated, for example, as a height/length ratio or as an absolute length. Other classification parameters can be, for example, the number of bends, the derivative of the movement in the x-direction and y-direction, crossings in the signature, curves and line ends. Other parameters can be the slope of letters and words. The determination and evaluation of the different parameters by the verification database can be done, for example, with the aid of statistical methods, frequency analysis, neural networks or some other classification method such as, for example, Nearest Neighbor. Normally, a classifier is used in these methods. A classifier can be "trained" by feeding in parameters and comparing the result obtained with the result required. If the result is not the one required, the classifier is adjusted and the parameters are fed in again and the result is compared with that required. This is continued until the required result is obtained. The verification database 2 checks 130 that the signature model is above an application-dependent uniqueness limit level . The signature model can also be compared with signature models stored earlier so that the signature written is not too similar to an existing signature. Depending on the application, the signature models should differ to a predetermined degree .

After the check, the verification database 2 delivers 140 a signal to the pen 1 which signal can comprise information that the signature is sufficiently unique or alternatively that it is not sufficiently unique. If the signature is not sufficiently unique, the signal can also include information about what the user can change in his signature. If the signature, for example, only consists of a line, which means that the number of bends is zero, and the limit level for the number of bends is determined to be greater than or equal to 10 for the signature to be determined to be unique, the checking arrangement will determine that the signature is not unique. The signal to the user unit can then inform the user that he or she must increase the number of bends in the signature. The check signal may as well be delivered to other receivers, such as a mobile telephone with a display, a PDA or a personal computer.

The information about which changes can be made can be presented by the areas in the signature which need to be changed being encircled, see Fig. 3. This information can be supplemented with a text message which tells the user which changes are required in the encircled areas.

Although a special embodiment of the invention has been described above, it is obvious to a person skilled in the art that many alternatives, modifications and variations are possible to be carried out in the light of the above description.

Claims

1. A system for analysing a user's signature, the system comprising a user unit (1) and a checking arrange- ent (2) , the user unit (1) being arranged to record a signature when the user writes with the user unit (1), and to send the signature to the checking arrangement (2) which is arranged to receive the signature, c h a r a c t e r i s e d in that the checking arrangement (2) is also arranged to build a signature model based on the signature, to make a check of the uniqueness of the signature model and, after the check, to deliver a signal, which indicates the uniqueness of the signature model.

2. A system according to claim 1, in which the signature model is the signature.

3. A system according to claim 1, in which the checking arrangement (2) is arranged to build up the signature model from a number of signatures received from the same user.

4. A system according to any one of the preceding claims, in which the checking arrangement (2) is arranged to calculate, in the check of the uniqueness of the signature model, at least one parameter which is characteristic of the signature model, and to make a check of said at least one parameter.

5. A system according to claim 4, in which the checking arrangement (2) is arranged to check, in the check of said at least one parameter, that said at least one parameter is above a predetermined uniqueness limit level.

6. A system according to claim 5, in which said signal contains information about what the user is to change in his signature for said at least one parameter to end up above the uniqueness limit level.

7. A system according to any one of the preceding claims, in which the checking arrangement (2) is also arranged to classify the signature.

8. A system according to any one of the preceding claims, in which the checking arrangement (2) is arranged to compare, in the check of the uniqueness of the signature model, the signature model with other signatures.

9. A system according to any one of the preceding claims, in which the signature is recorded as a sequence of coordinates which describe the displacement of the user unit (1) when the user writes his signature with the user unit (1) .

10. A system according to claim 9, further comprising a base (5) which is provided with a position-coding pattern (7) which enables the coordinates to be calculated and from which the user unit (1) is arranged to record the sequence of coordinates .

11. A system according to any one of the preceding claims, in which the user unit (1) comprises an optical sensor (14) and image-processing means (16) for recording the signature.

12. A system according to any one of the preceding claims, in which the checking arrangement (2) is arranged in a verification database.

13. A checking arrangement for analysing a user's signature, which is written with a user unit (1) , the checking arrangement (2) being arranged to receive the signature, c ha r a c t e r i s e d in that the checking arrangement (2) is also arranged to build a signature model based on the signature, to make a check of the uniqueness of the signature model and to deliver a signal, which indicates the uniqueness of the signature model .

14. A checking arrangement according to claim 13, in which the signature model is the signature.

15. A checking arrangement according to claim 13, in which the checking arrangement (2) is arranged to build up the signature model of a number of signatures received from the same user.

16. A checking arrangement according to any one of claims 13-15, which is arranged to calculate, in the check of the uniqueness of the signature model, at least one parameter characteristic of the signature model and to make a check of said at least one parameter.

17. A checking arrangement according to any one of claims 13-16, in which said signal comprises information about what the user is to change in the signature for it to attain a certain uniqueness.

18.- A checking arrangement according to any one of claims 13-17, which is arranged in a verification database .

19. A method for analysing a signature comprising the following steps: recording a signature with the aid of a user unit (1) , sending on a representation of the signature to a checking arrangement (2), building up a signature model in the checking arrangement (2), making a. check of the uniqueness of the signature model in the checking arrangement (2), and after the check, delivering a signal, which indicates the uniqueness of the signature model.

20. A method according to claim 19, in which the check of the uniqueness of the signature model comprises the following steps: calculating at least one parameter characteristic of the signature model, and making a check of said at least one parameter.

21. A method according to any one of claims 19 or 20, comprising the step of classifying the signature.

22. A method according to any one of claims 19-21, comprising the step of comparing the signature model with other signatures.

23. A method for analysing a user's signature, which is written by a user unit comprising the following steps: receiving the signature, building a signature model based on the signature, making a check of the uniqueness of the signature model, and delivering a signal, which indicates the uniqueness of the signature model.

24. A method according to claim 23, in which the step of making a check of the uniqueness of the signature model comprises the following steps: calculating at least one parameter characteristic of the signature model, and making a check of at least one parameter.

25. A method according to any one of claims 23 or 24, comprising the step of classifying the signature.

26. A method according to any one of claims 23-25, comprising the step of comparing the signature model with other signatures.

27. A computer program product directly loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of any of rl?iτn 9 -9fi when _"=;aid nror1'r^,f i <= run on a coπrnuter.