Patent Publication Number: US-2007113076-A1

Title: Keys

Description:
This application claims priority to and incorporates by reference U.S. provisional application No. 60/702,742 filed on Jul. 27, 2005, and Great Britain patent application GB 0515463.8 filed on Jul. 27, 2005. 
    
    
     FIELD  
      The present invention relates to keys, and in particular but not exclusively, to distribution of encryption keys.  
      In many applications where secure transmission of data is required, data encryption can be used to impede unauthorised access to that data. Conventional encryption schemes work on one of two methods: symmetric and asymmetric key methods.  
      Symmetric key systems use the same key for encryption and decryption of data. Thus the key must be distributed between participants in an exchange of encrypted data. If the key is not distributed securely, it is possible for third parties to obtain a copy of the key and to use that copy to access all data encrypted using the key.  
      Asymmetric key systems work on a one way encryption scheme where a public key is used to encrypt data, which can then only be decrypted using a private key which is kept by the recipient of the data. Thus the public key can be freely distributed and anything encrypted using the key can only be decrypted using the private key. However in such a system, it can still be desirable that the public key is distributed such that a person receiving the public key can be certain that it comes from the intended recipient of a secure communication. If this is not the case, there is a possibility of a third party creating a public key which appears to belong to someone else and using that public key and its corresponding private key to access encrypted data intended for the apparent originator of the key.  
      A data packaging technique has been discussed in Gershenfeld, Science 297 (5589): 20026-2030, Sep. 20, 2002). The technique disclosed thereby uses a very specific optically transparent three-dimensional token to create wrapping data.  
     SUMMARY  
      The present invention has been made, at least in part, in consideration of problems and drawbacks of conventional systems.  
      The present invention has at least in part resulted from the inventor&#39;s work on applying authentication techniques using tokens made of magnetic materials, where the uniqueness is provided by unreproducible defects in the magnetic material that affect the token&#39;s magnetic response (as detailed in PCT/GB03/03917, Cowburn). As part of this work, magnetic materials were fabricated in barcode format, i.e. as a number of parallel strips. As well as reading the unique magnetic response of the strips by sweeping a magnetic field with a magnetic reader, an optical scanner was built to read the barcodes by scanning a laser beam over the barcode and using contrast from the varying reflectivity of the barcode strips and the article on which they were formed. This information was complementary to the magnetic characteristic, since the barcode was being used to encode a digital signature of the unique magnetic response in a type of well known self authentication scheme, for example as also described above for banknotes (see for example, Kravolec “Plastic tag makes foolproof ID”, Technology research news, 2 Oct. 2002).  
      To the surprise of the inventor, it was discovered when using this optical scanner that the paper background material on which the magnetic chips were supported gave a unique optical response to the scanner. On further investigation, it was established that many other unprepared surfaces, such as surfaces of various types of cardboard and plastic, show the same effect. Moreover, it has been established by the inventor that the unique characteristic arises at least in part from speckle, but also includes non-speckle contributions.  
      It has thus been discovered that it is possible to gain all the advantages of speckle based techniques without having to use a specially prepared token or specially prepare an article in any other way. In particular, many types of paper, cardboard and plastics have been found to give unique characteristic scattering signals from a coherent light beam, so that unique digital signatures can be obtained from almost any paper document or cardboard packaging item.  
      The above-described known speckle readers used for security devices appear to be based on illuminating the whole of a token with a laser beam and imaging a significant solid angle portion of the resultant speckle pattern with a CCD (see for example GB 2 221 870 and U.S. Pat. No. 6,584,214), thereby obtaining a speckle pattern image of the token made up of a large array of data points.  
      The reader used by the inventor does not operate in this manner. It uses four single channel detectors (four simple phototransistors) which are angularly spaced apart to collect only four signal components from the scattered laser beam. The laser beam is focused to a spot covering only a very small part of the surface. Signal is collected from different localised areas on the surface by the four single channel detectors as the spot is scanned over the surface. The characteristic response from the article is thus made up of independent measurements from a large number (typically hundreds or thousands) of different localised areas on the article surface. Although four phototransistors are used, analysis using only data from a single one of the phototransistors shows that a unique characteristic response can be derived from this single channel alone! However, higher security levels are obtained if further ones of the four channels are included in the response.  
      Viewed from a first aspect, the present invention provides a method for the distribution of a key. The method can comprise packaging a key using a signature based upon an intrinsic property of a security token, transmitting the packaged key to a recipient location, and unpacking the key using a signature based upon the intrinsic property of the security token. Thus the key can be securely transmitted in such a way that a third party intercepting the transmission but not in possession of the security token cannot access the key. In some examples, data encrypted using the key may be transmitted with the packaged key such that the recipient can instantly access the encrypted data. In other examples, the key can be transmitted alone for later encryption or decryption use. Such a key may be a key of an asymmetric encryption key pair.  
      In some embodiments, the packaging can comprise creating error correction code data for the key and packaging the key and the error correction code data using the signature, and the unpacking can comprise unpacking the key and the error correction code data and using the error correction code data to undo any errors in the key. Thus non-identical biometric type signatures taken from the same security token can be used to package and unpack the key without errors occurring in the unpacked key. In some embodiments, the key can include redundant data, or redundant data can be added to the key in order to enhance the effectiveness of the error correction process.  
      In some embodiments the packaging can comprise performing a bitwise exclusive-OR operation between the key and the signature, and the unpacking can comprise performing a bitwise exclusive-OR operation between the packaged key and the signature. Thus an easily repeatable, reversible process for packaging the key is available, which does not make the key or the signature available to a third party monitoring transmission of the packaged key.  
      As the signature is typically based upon a biometric type analysis of the security token, the signature used in the packaging step may be different to the signature used in the unpacking step. However, both signatures are based upon the same intrinsic characteristic of the same security token.  
      In some examples, each signature is created by exposing the security token to coherent radiation, collecting a set of data points that measure scatter of the coherent radiation from intrinsic structure of the security token and determining a signature of the security token from the set of data points.  
      Viewed from a second aspect, the present invention provides a method of transmitting encrypted data. The method can comprise encrypting data using an encryption key, packaging a decryption key using a signature based upon an intrinsic property of a security token, transmitting the packaged key and encrypted data to a recipient location, unpacking the key using a signature based upon the intrinsic property of the security token, and decrypting the data using the unpacked key. Thus the data can be transmitted securely in an encrypted form in such a way that an authorised recipient thereof in possession of the security token can access the necessary decryption key and thus the data, whilst a third party intercepting the transmission cannot gain access to the key or the data. In some examples, the encryption and decryption keys are the same. In other examples, an asymmetric encryption/decryption key pair may be used.  
      In some embodiments, a transaction such as an e-commerce transaction may be carried out. In such a transaction, the encrypted data may relate to financial information for value transfer as part of the transaction. The security token may be an access token associated with value transfer such as a bank, credit or loyalty card.  
      In some embodiments, the data may be data sent from a database in response to an access request. The access request may have been based upon a signature obtained from a database access token. The database access token may be the same physical article as the security token, with different areas or resolutions of the article being used to create the different signatures.  
      In some examples, one party may maintain a database of security token signatures, and different ones of the signatures to communicate with different persons or entities.  
      Viewed from another aspect, the present invention provides a key distribution system. The system can comprise a key packaging unit operable to package a key using a signature based upon an intrinsic property of a security token, a channel operable to have the packaged key transmitted therethrough; and a key unpacking unit operable to unpack the key using a signature based upon the intrinsic property of the security token. Thereby the key can be transmitted via a non-secure channel to a recipient for use thereby, without it being possible for a third party to obtain a copy of the key by monitoring the channel.  
      Viewed from another aspect, the present invention can provide an encrypted data transmission system. The system can comprise an encryption unit operable to encrypt data using an encryption key, a packaging unit operable to package the key using a signature based upon an intrinsic property of a security token, a channel operable to have the packaged key and encrypted data transmitted therethrough, an unpacking unit operable to unpack the key using a signature based upon the intrinsic property of the security token, and a decryption unit operable to decrypt the data using the unpacked key. Thereby the data can be securely transmitted in a manner which enables the recipient to easily access the encrypted data.  
      In some examples, one key may be transmitted for use in accessing more than one data packet. For example, a particular financial or data access transaction may be secured using a single key which can be transmitted at the beginning of the transaction for use therein.  
      In some embodiments, it is ensured that different ones of the data gathered in relation to the intrinsic property of the article relate to scatter from different parts of the article by providing for movement of the coherent beam relative to the article. The movement may be provided by a motor that moves the beam over an article that is held fixed. The motor could be a servo motor, free running motor, stepper motor or any suitable motor type. Alternatively, the drive could be manual in a low cost reader. For example, the operator could scan the beam over the article by moving a carriage on which the article is mounted across a static beam. The coherent beam cross-section will usually be at least one order of magnitude (preferably at least two) smaller than the projection of the article so that a significant number of independent data points can be collected. A focusing arrangement may be provided for bringing the coherent beam into focus in the article. The focusing arrangement may be configured to bring the coherent beam to an elongate focus, in which case the drive is preferably configured to move the coherent beam over the article in a direction transverse to the major axis of the elongate focus. An elongate focus can conveniently be provided with a cylindrical lens, or equivalent mirror arrangement.  
      In other embodiments, it can be ensured that different ones of the data points relate to scatter from different parts of the article, in that the detector arrangement includes a plurality of detector channels arranged and configured to sense scatter from respective different parts of the article. This can be achieved with directional detectors, local collection of signal with optical fibres or other measures. With directional detectors or other localised collection of signal, the coherent beam does not need to be focused. Indeed, the coherent beam could be static and illuminate the whole sampling volume. Directional detectors could be implemented by focusing lenses fused to, or otherwise fixed in relation to, the detector elements. Optical fibres may be used in conjunction with microlenses.  
      It is possible to make a workable reader when the detector arrangement consists of only a single detector channel. Other embodiments use a detector arrangement that comprises a group of detector elements angularly distributed and operable to collect a group of data points for each different part of the reading volume, preferably a small group of a few detector elements. Security enhancement is provided when the signature incorporates a contribution from a comparison between data points of the same group. This comparison may conveniently involve a cross-correlation.  
      Although a working reader can be made with only one detector channel, there are preferably at least 2 channels. This allows cross-correlations between the detector signals to be made, which is useful for the signal processing associated with determining the signature. It is envisaged that between 2 and 10 detector channels will be suitable for most applications with 2 to 4 currently being considered as the optimum balance between apparatus simplicity and security.  
      The detector elements are advantageously arranged to lie in a plane intersecting the reading volume with each member of the pair being angularly distributed in the plane in relation to the coherent beam axis, preferably with one or more detector elements either side of the beam axis. However, non-planar detector arrangements are also acceptable.  
      The use of cross-correlations of the signals obtained from the different detectors has been found to give valuable data for increasing the security levels and also for allowing the signatures to be more reliably reproducible over time. The utility of the cross-correlations is somewhat surprising from a scientific point of view, since speckle patterns are inherently uncorrelated (with the exception of signals from opposed points in the pattern). In other words, for a speckle pattern there will by definition be zero cross-correlation between the signals from the different detectors so long as they are not arranged at equal magnitude angles offset from the excitation location in a common plane intersecting the excitation location. The value of using cross-correlation contributions therefore indicates that an important part of the scatter signal is not speckle. The non-speckle contribution could be viewed as being the result of direct scatter, or a diffuse scattering contribution, from a complex surface, such as paper fibre twists. At present the relative importance of the speckle and non-speckle scatter signal contribution is not clear. However, it is clear from the experiments performed to date that the detectors are not measuring a pure speckle pattern, but a composite signal with speckle and non-speckle components.  
      Incorporating a cross-correlation component in the signature can also be of benefit for improving security. This is because, even if it is possible using high resolution printing to make an article that reproduces the contrast variations over the surface of the genuine article, this would not be able to match the cross-correlation coefficients obtained by scanning the genuine article.  
      In the one embodiment, the detector channels are made up of discrete detector components in the form of simple phototransistors. Other simple discrete components could be used such as PIN diodes or photodiodes. Integrated detector components, such as a detector array could also be used, although this would add to the cost and complexity of the device.  
      From initial experiments which modify the illumination angle of the laser beam on the article to be scanned, it also seems to be preferable in practice that the laser beam is incident approximately normal to the surface being scanned in order to obtain a characteristic that can be repeatedly measured from the same surface with little change, even when the article is degraded between measurements. At least some known readers use oblique incidence (see GB 2 221 870). Once appreciated, this effect seems obvious, but it is clearly not immediately apparent as evidenced by the design of some prior art speckle readers including that of GB 2 221 870 and indeed the first prototype reader built by the inventor. The inventor&#39;s first prototype reader with oblique incidence functioned reasonably well in laboratory conditions, but was quite sensitive to degradation of the paper used as the article. For example, rubbing the paper with fingers was sufficient to cause significant differences to appear upon re-measurement. The second prototype reader used normal incidence and has been found to be robust against degradation of paper by routine handling, and also more severe events such as: passing through various types of printer including a laser printer, passing through a photocopier machine, writing on, printing on, deliberate scorching in an oven, and crushing and reflattening.  
      It can therefore be advantageous to mount the source so as to direct the coherent beam onto the reading volume so that it will strike an article with near normal incidence. By near normal incidence means ±5, 10 or 20 degrees. Alternatively, the beam can be directed to have oblique incidence on the articles. This will usually have a negative influence in the case that the beam is scanned over the article.  
      It is also noted that in the readers described in the detailed description, the detector arrangement is arranged in reflection to detect radiation back scattered from the reading volume. However, if the article is transparent, the detectors could be arranged in transmission.  
      A signature generator can be operable to access the database of previously recorded signatures and perform a comparison to establish whether the database contains a match to the signature of an article that has been placed in the reading volume. The database may be part of a mass storage device that forms part of the reader apparatus, or may be at a remote location and accessed by the reader through a telecommunications link. The telecommunications link may take any conventional form, including wireless and fixed links, and may be available over the internet. The data acquisition and processing module may be operable, at least in some operational modes, to allow the signature to be added to the database if no match is found.  
      When using a database, in addition to storing the signature it may also be useful to associate that signature in the database with other information about the article such as a scanned copy of the document, a photograph of a passport holder, details on the place and time of manufacture of the product, or details on the intended sales destination of vendable goods (e.g. to track grey importation).  
      The invention allows identification of articles made of a variety of different kinds of materials, such as paper, cardboard and plastic.  
      By intrinsic structure we mean structure that the article inherently will have by virtue of its manufacture, thereby distinguishing over structure specifically provided for security purposes, such as structure given by tokens or artificial fibres incorporated in the article.  
      By paper or cardboard we mean any article made from wood pulp or equivalent fibre process. The paper or cardboard may be treated with coatings or impregnations or covered with transparent material, such as cellophane. If long-term stability of the surface is a particular concern, the paper may be treated with an acrylic spray-on transparent coating, for example.  
      Data points can thus be collected as a function of position of illumination by the coherent beam. This can be achieved either by scanning a localised coherent beam over the article, or by using directional detectors to collect scattered light from different parts of the article, or by a combination of both.  
      The signature is envisaged to be a digital signature in most applications. Typical sizes of the digital signature with current technology would be in the range 200 bits to 8 k bits, where currently it is preferable to have a digital signature size of about 2 k bits for high security.  
      A further implementation of the invention can be performed without storing the digital signatures in a database, but rather by labelling the entitlement token with a label derived from the signature, wherein the label conforms to a machine-readable encoding protocol.  
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
      Specific embodiments of the present invention will now be described by way of example only with reference to the accompanying figures in which:  
       FIG. 1  is a schematic side view of an example of a reader apparatus;  
       FIG. 2  is a schematic perspective view showing how the reading volume of the reader apparatus of  FIG. 1  is sampled;  
       FIG. 3  is a block schematic diagram of the functional components of the reader apparatus of  FIG. 1 ;  
       FIG. 4  is a perspective view of the reader apparatus of  FIG. 1  showing its external form;  
       FIG. 5  is a perspective view showing another example of an external form for the reader of  FIG. 1 ;  
       FIG. 6A  is schematic cross-sectional view through an alternative reader configuration;  
       FIG. 6B  is a perspective view of another alternative reader configuration;  
       FIG. 6C  is a perspective view of another alternative reader configuration;  
       FIG. 7A  shows schematically in side view an alternative imaging arrangement for a reader based on directional light collection and blanket illumination;  
       FIG. 7B  shows schematically in plan view the optical footprint of a further alternative imaging arrangement for a reader in which directional detectors are used in combination with localised illumination with an elongate beam;  
       FIG. 8A  is a microscope image of a paper surface with the image covering an area of approximately 0.5×0.2 mm;  
       FIG. 8B  is a microscope image of a plastic surface with the image covering an area of approximately 0.02×0.02 mm;  
       FIG. 9A  shows raw data from a single photodetector using the reader of  FIG. 1  which consists of a photodetector signal and an encoder signal;  
       FIG. 9B  shows the photodetector data of  FIG. 9A  after linearisation with the encoder signal and averaging the amplitude;  
       FIG. 9C  shows the data of  FIG. 9B  after digitisation according to the average level;  
       FIG. 10  is a flow diagram showing how a signature of an article is generated from a scan;  
       FIG. 11  is a flow diagram showing how a signature of an article obtained from a scan can be verified against a signature database;  
       FIG. 12  is a flow diagram showing how the verification process of  FIG. 11  can be altered to account for non-idealities in a scan;  
       FIG. 13A  shows an example of cross-correlation data gathered from a scan;  
       FIG. 13   b  shows an example of cross-correlation data gathered from a scan where the scanned article is distorted;  
       FIG. 13C  shows an example of cross-correlation data gathered from a scan where the scanned article is scanned at non-linear speed;  
       FIG. 14  shows a schematic representation of an article for verification;  
       FIG. 15  is a schematic cut-away perspective view of a multi-scan head scanner;  
       FIG. 16  is a schematic cut-away perspective view of a multi-scan head position scanner;  
       FIG. 17  shows schematically a system for packaging an encryption key; and  
       FIG. 18  shows schematically a system for unpacking of a packaged encryption key. 
    
    
      While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.  
     DESCRIPTION OF PARTICULAR EMBODIMENTS  
      For providing security and authorization services in environments such as an e-commerce environment, a system for uniquely identifying a physical item can be used to reduce possibilities for fraud, and to enhance both actual and perceived reliability of the e-commerce system, for both provider and end-users.  
      Examples of systems suitable for performing such item identification will now be described with reference to FIGS.  1  to  11 .  
       FIG. 1  shows a schematic side view of a first example of a reader apparatus  1 . The optical reader apparatus  1  is for measuring a signature from an article (not shown) arranged in a reading volume of the apparatus. The reading volume is formed by a reading aperture  10  which is a slit in a housing  12 . The housing  12  contains the main optical components of the apparatus. The slit has its major extent in the x direction (see inset axes in the drawing). The principal optical components are a laser source  14  for generating a coherent laser beam  15  and a detector arrangement  16  made up of a plurality of k photodetector elements, where k=4 in this example, labelled  16   a ,  16   b ,  16   c  and  16   d . The laser beam  15  is focused by a cylindrical lens  18  into an elongate focus extending in the y direction (perpendicular to the plane of the drawing) and lying in the plane of the reading aperture. In one example reader, the elongate focus has a major axis dimension of about 2 mm and a minor axis dimension of about 40 micrometres. These optical components are contained in a subassembly  20 . In the present example, the four detector elements  16   a . . . d  are distributed either side of the beam axis offset at different angles in an interdigitated arrangement from the beam axis to collect light scattered in reflection from an article present in the reading volume. In the present example, the offset angles are −70, −20, +30 and +50 degrees. The angles either side of the beam axis are chosen so as not to be equal so that the data points they collect are as independent as possible. All four detector elements are arranged in a common plane. The photodetector elements  16   a . . . d  detect light scattered from an article placed on the housing when the coherent beam scatters from the reading volume. As illustrated, the source is mounted to direct the laser beam  15  with its beam axis in the z direction, so that it will strike an article in the reading aperture at normal incidence.  
      Generally it is desirable that the depth of focus is large, so that any differences in the article positioning in the z direction do not result in significant changes in the size of the beam in the plane of the reading aperture. In the present example, the depth of focus is approximately 0.5 mm which is sufficiently large to produce good results where the position of the article relative to the scanner can be controlled to some extent. The parameters, of depth of focus, numerical aperture and working distance are interdependent, resulting in a well known trade off between spot size and depth of focus.  
      A drive motor  22  is arranged in the housing  12  for providing linear motion of the optics subassembly  20  via suitable bearings  24  or other means, as indicated by the arrows  26 . The drive motor  22  thus serves to move the coherent beam linearly in the x direction over the reading aperture  10  so that the beam  15  is scanned in a direction transverse to the major axis of the elongate focus. Since the coherent beam  15  is dimensioned at its focus to have a cross-section in the xz plane (plane of the drawing) that is much smaller than a projection of the reading volume in a plane normal to the coherent beam, i.e. in the plane of the housing wall in which the reading aperture is set, a scan of the drive motor  22  will cause the coherent beam  15  to sample many different parts of the reading volume under action of the drive motor  22 .  
       FIG. 2  is included to illustrate this sampling and is a schematic perspective view showing how the reading area is sampled n times by scanning an elongate beam across it. The sampling positions of the focused laser beam as it is scanned along the reading aperture under action of the drive is represented by the adjacent rectangles numbered 1 to n which sample an area of length ‘l’ and width ‘w’. Data collection is made so as to collect signal at each of the n positions as the drive is scanned along the slit. Consequently, a sequence of k×n data points are collected that relate to scatter from the n different illustrated parts of the reading volume.  
      Also illustrated schematically are optional distance marks  28  formed on the underside of the housing  12  adjacent the slit  10  along the x direction, i.e. the scan direction. An example spacing between the marks in the x-direction is 300 micrometres. These marks are sampled by a tail of the elongate focus and provide for linearisation of the data in the x direction in situations where such linearisation is required, as is described in more detail further below. The measurement is performed by an additional phototransistor  19  which is a directional detector arranged to collect light from the area of the marks  28  adjacent the slit.  
      In alternative examples, the marks  28  can be read by a dedicated encoder emitter/detector module  19  that is part of the optics subassembly  20 . Encoder emitter/detector modules are used in bar code readers. In one example, an Agilent HEDS-1500 module that is based on a focused light emitting diode (LED) and photodetector can be used. The module signal is fed into the PIC ADC as an extra detector channel (see discussion of  FIG. 3  below).  
      With an example minor dimension of the focus of 40 micrometers, and a scan length in the x direction of 2 cm, n=500, giving 2000 data points with k=4. A typical range of values for k×n depending on desired security level, article type, number of detector channels ‘k’ and other factors is expected to be 100&lt;k×n&lt;10,000. It has also been found that increasing the number of detectors k also improves the insensitivity of the measurements to surface degradation of the article through handling, printing etc. In practice, with the prototypes used to date, a rule of thumb is that the total number of independent data points, i.e. k×n, should be 500 or more to give an acceptably high security level with a wide variety of surfaces. Other minima (either higher or lower) may apply where a scanner is intended for use with only one specific surface type or group of surface types.  
       FIG. 3  is a block schematic diagram of functional components of the reader apparatus. The motor  22  is connected to a programmable interrupt controller (PIC)  30  through an electrical link  23 . The detectors  16   a . . . d  of the detector module  16  are connected through respective electrical connection lines  17   a . . . d  to an analogue-to-digital converter (ADC) that is part of the PIC  30 . A similar electrical connection line  21  connects the marker reading detector  19  to the PIC  30 . It will be understood that optical or wireless links may be used instead of, or in combination with, electrical links. The PIC  30  is interfaced with a personal computer (PC)  34  through a data connection  32 . The PC  34  may be a desktop or a laptop. As an alternative to a PC, other intelligent devices may be used, for example a personal digital assistant (PDA) or a dedicated electronics unit. The PIC  30  and PC  34  collectively form a data acquisition and processing module  36  for determining a signature of the article from the set of data points collected by the detectors  16   a . . . d.    
      In some examples, the PC  34  can have access through an interface connection  38  to a database (dB)  40 . The database  40  may be resident on the PC  34  in memory, or stored on a drive thereof. Alternatively, the database  40  may be remote from the PC  34  and accessed by wireless communication, for example using mobile telephony services or a wireless local area network (LAN) in combination with the internet. Moreover, the database  40  may be stored locally on the PC  34 , but periodically downloaded from a remote source. The database may be administered by a remote entity, which entity may provide access to only a part of the total database to the particular PC  34 , and/or may limit access the database on the basis of a security policy.  
      The database  40  can contain a library of previously recorded signatures. The PC  34  can be programmed so that in use it can access the database  40  and performs a comparison to establish whether the database  40  contains a match to the signature of the article that has been placed in the reading volume. The PC  34  can also be programmed to allow a signature to be added to the database if no match is found.  
      The way in which data flow between the PC and database is handled can be dependent upon the location of the PC and the relationship between the operator of the PC and the operator of the database. For example, if the PC and reader are being used to confirm the authenticity of an article, then the PC will not need to be able to add new articles to the database, and may in fact not directly access the database, but instead provide the signature to the database for comparison. In this arrangement the database may provide an authenticity result to the PC to indicate whether the article is authentic. On the other hand, if the PC and reader are being used to record or validate an item within the database, then the signature can be provided to the database for storage therein, and no comparison may be needed. In this situation a comparison could be performed however, to avoid a single item being entered into the database twice.  
       FIG. 4  is a perspective view of the reader apparatus  1  showing its external form. The housing  12  and slit-shaped reading aperture  10  are evident. A physical location aid  42  is also apparent and is provided for positioning an article of a given form in a fixed position in relation to the reading aperture  10 . In the present example, the physical location aid  42  is in the form of a right-angle bracket in which the corner of a document or packaging box can be located. This ensures that the same part of the article can be positioned in the reading aperture  10  whenever the article needs to be scanned. A simple angle bracket or equivalent, is sufficient for articles with a well-defined corner, such as sheets of paper, passports, ID cards and packaging boxes. Other shaped position guides could be provided to accept items of different shapes, such as circular items including CDs and DVDs, or items with curved surfaces such as cylindrical packaging containers. Where only one size and shape of item is to be scanned a slot may be provided for receiving the item.  
      Thus there has now been described an example of a scanning and signature generation apparatus suitable for use in a security mechanism for remote verification of article authenticity. Such a system can be deployed to allow an article to be scanned in more than one location, and for a check to be performed to ensure that the article is the same article in both instances, and optionally for a check to performed to ensure that the article has not been tampered with between initial and subsequent scannings.  
       FIG. 5  shows an example of an alternative physical configuration for a reader where a document feeder is provided to ensure that article placement is consistent. In this example, a housing  60  is provided, having an article feed tray  61  attached thereto. The tray  61  can hold one or more articles  62  for scanning by the reader. A motor can drive feed rollers  64  to carry an article  62  through the device and across a scanning aperture of an optics subassembly  20  as described above. Thus the article  62  can be scanned by the optics subassembly  20  in the manner discussed above in a manner whereby the relative motion between optics subassembly and article is created by movement of the article. Using such a system, the motion of the scanned item can be controlled using the motor with sufficient linearity that the use of distance marks and linearisation processing may be unnecessary. The apparatus could follow any conventional format for document scanners, photocopiers or document management systems. Such a scanner may be configured to handle line-feed sheets (where multiple sheets are connected together by, for example, a perforated join) as well as or instead of handing single sheets.  
      Thus there has now been described an apparatus suitable for scanning articles in an automated feeder type device. Depending upon the physical arrangement of the feed arrangement, the scanner may be able to scan one or more single sheets of material, joined sheets or material or three-dimensional items such as packaging cartons.  
       FIG. 6  show examples of further alternative physical configurations for a reader. In this example, the article is moved through the reader by a user. As shown in  FIG. 6A , a reader housing  70  can be provided with a slot  71  therein for insertion of an article for scanning. An optics subassembly  20  can be provided with a scanning aperture directed into the slot  71  so as to be able to scan an article  62  passed through the slot. Additionally, guide elements  72  may be provided in the slot  71  to assist in guiding the article to the correct focal distance from the optics sub-assembly  20  and/or to provide for a constant speed passage of the article through the slot.  
      As shown in  FIG. 6B , the reader may be configured to scan the article when moved along a longitudinal slot through the housing  70 , as indicated by the arrow. Alternatively, as shown in  FIG. 6C , the reader may be configured to scan the article when inserted into or removed from a slot extending into the reader housing  70 , as indicated by the arrow. Scanners of this type may be particularly suited to scanning articles which are at least partially rigid, such as card, plastic or metal sheets. Such sheets may, for example, be plastic items such as credit cards or other bank cards.  
      Thus there have now been described an arrangement for manually initiated scanning of an article. This could be used for scanning bank cards and/or credit cards. Thereby a card could be scanned at a terminal where that card is presented for use, and a signature taken from the card could be compared to a stored signature for the card to check the authenticity and un-tampered nature of the card. Such a device could also be used, for example in the context of reading a military-style metal ID-tag (which tags are often also carried by allergy sufferers to alert others to their allergy). This could enable medical personnel treating a patient to ensure that the patient being treated was in fact the correct bearer of the tag. Likewise, in a casualty situation, a recovered tag could be scanned for authenticity to ensure that a casualty has been correctly identified before informing family and/or colleagues.  
      The above-described examples are based on localised excitation with a coherent light beam of small cross-section in combination with detectors that accept light signal scattered over a much larger area that includes the local area of excitation. It is possible to design a functionally equivalent optical system which is instead based on directional detectors that collect light only from localised areas in combination with excitation of a much larger area.  
       FIG. 7A  shows schematically in side view such an imaging arrangement for a reader which is based on directional light collection and blanket illumination with a coherent beam. An array detector  48  is arranged in combination with a cylindrical microlens array  46  so that adjacent strips of the detector array  48  only collect light from corresponding adjacent strips in the reading volume. With reference to  FIG. 2 , each cylindrical microlens is arranged to collect light signal from one of the n sampling strips. The coherent illumination can then take place with blanket illumination of the whole reading volume (not shown in the illustration).  
      A hybrid system with a combination of localised excitation and localised detection may also be useful in some cases.  
       FIG. 7B  shows schematically in plan view the optical footprint of such a hybrid imaging arrangement for a reader in which directional detectors are used in combination with localised illumination with an elongate beam. This example may be considered to be a development of the example of  FIG. 1  in which directional detectors are provided. In this example three banks of directional detectors are provided, each bank being targeted to collect light from different portions along the ‘l×w’ excitation strip. The collection area from the plane of the reading volume are shown with the dotted circles, so that a first bank of, for example 2, detectors collects light signal from the upper portion of the excitation strip, a second bank of detectors collects light signal from a middle portion of the excitation strip and a third bank of detectors collects light from a lower portion of the excitation strip. Each bank of detectors is shown having a circular collection area of diameter approximately l/m, where m is the number of subdivisions of the excitation strip, where m=3 in the present example. In this way the number of independent data points can be increased by a factor of m for a given scan length l. As described further below, one or more of different banks of directional detectors can be used for a purpose other than collecting light signal that samples a speckle pattern. For example, one of the banks may be used to collect light signal in a way optimised for barcode scanning. If this is the case, it will generally be sufficient for that bank to contain only one detector, since there will be no advantage obtaining cross-correlations when only scanning for contrast.  
      Having now described the principal structural components and functional components of various reader apparatuses, the numerical processing used to determine a signature will now be described. It will be understood that this numerical processing can be implemented for the most part in a computer program that runs on the PC  34  with some elements subordinated to the PIC  30 . In alternative examples, the numerical processing could be performed by a dedicated numerical processing device or devices in hardware or firmware.  
       FIG. 8A  is a microscope image of a paper surface with the image covering an area of approximately 0.5×0.2 mm. This figure is included to illustrate that macroscopically flat surfaces, such as from paper, are in many cases highly structured at a microscopic scale. For paper, the surface is microscopically highly structured as a result of the intermeshed network of wood or other fibres that make up the paper. The figure is also illustrative of the characteristic length scale for the wood fibres which is around 10 microns. This dimension has the correct relationship to the optical wavelength of the coherent beam of the present example to cause diffraction and hence speckle, and also diffuse scattering which has a profile that depends upon the fibre orientation. It will thus be appreciated that if a reader is to be designed for a specific class of goods, the wavelength of the laser can be tailored to the structure feature size of the class of goods to be scanned. It is also evident from the figure that the local surface structure of each piece of paper will be unique in that it depends on how the individual wood fibres are arranged. A piece of paper is thus no different from a specially created token, such as the special resin tokens or magnetic material deposits of the prior art, in that it has structure which is unique as a result of it being made by a process governed by laws of nature. The same applies to many other types of article.  
       FIG. 8B  shows an equivalent image for a plastic surface. This atomic force microscopy image clearly shows the uneven surface of the macroscopically smooth plastic surface. As can be surmised from the figure, this surface is smoother than the paper surface illustrated in  FIG. 8A , but even this level of surface undulation can be uniquely identified using the signature generation scheme of the present example.  
      In other words, it can be essentially pointless to go to the effort and expense of making specially prepared tokens, when unique characteristics are measurable in a straightforward manner from a wide variety of every day articles. The data collection and numerical processing of a scatter signal that takes advantage of the natural structure of an article&#39;s surface (or interior in the case of transmission) is now described.  
       FIG. 9A  shows raw data from a single one of the photodetectors  16   a . . . d  of the reader of  FIG. 1 . The graph plots signal intensity I in arbitrary units (a.u.) against point number n (see  FIG. 2 ). The higher trace fluctuating between I=0−250 is the raw signal data from photodetector  16   a . The lower trace is the encoder signal picked up from the markers  28  (see  FIG. 2 ) which is at around I=50.  
       FIG. 9B  shows the photodetector data of  FIG. 9A  after linearisation with the encoder signal (n.b. although the x axis is on a different scale from  FIG. 9A , this is of no significance). As noted above, where a movement of the article relative to the scanner is sufficiently linear, there may be no need to make use of a linearisation relative to alignment marks. In addition, the average of the intensity has been computed and subtracted from the intensity values. The processed data values thus fluctuate above and below zero.  
       FIG. 9C  shows the data of  FIG. 9B  after digitisation. The digitisation scheme adopted is a simple binary one in which any positive intensity values are set at value 1 and any negative intensity values are set at zero. It will be appreciated that multi-state digitisation could be used instead, or any one of many other possible digitisation approaches. The main important feature of the digitisation is merely that the same digitisation scheme is applied consistently.  
       FIG. 10  is a flow diagram showing how a signature of an article is generated from a scan.  
      Step S 1  is a data acquisition step during which the optical intensity at each of the photodetectors is acquired approximately every 1 ms during the entire length of scan. Simultaneously, the encoder signal is acquired as a function of time. It is noted that if the scan motor has a high degree of linearisation accuracy (e.g. as would a stepper motor) then linearisation of the data may not be required. The data is acquired by the PIC  30  taking data from the ADC  31 . The data points are transferred in real time from the PIC  30  to the PC  34 . Alternatively, the data points could be stored in memory in the PIC  30  and then passed to the PC  34  at the end of a scan. The number n of data points per detector channel collected in each scan is defined as N in the following. Further, the value a k (i) is defined as the i-th stored intensity value from photodetector k, where i runs from 1 to N. Examples of two raw data sets obtained from such a scan are illustrated in  FIG. 9A .  
      Step S 2  uses numerical interpolation to locally expand and contract a k (i) so that the encoder transitions are evenly spaced in time. This corrects for local variations in the motor speed. This step can be performed in the PC  34  by a computer program.  
      Step S 3  is an optional step. If performed, this step numerically differentiates the data with respect to time. It may also be desirable to apply a weak smoothing function to the data. Differentiation may be useful for highly structured surfaces, as it serves to attenuate uncorrelated contributions from the signal relative to correlated (speckle) contributions.  
      Step S 4  is a step in which, for each photodetector, the mean of the recorded signal is taken over the N data points. For each photodetector, this mean value is subtracted from all of the data points so that the data are distributed about zero intensity. Reference is made to  FIG. 9B  which shows an example of a scan data set after linearisation and subtraction of a computed average.  
      Step S 5  digitises the analogue photodetector data to compute a digital signature representative of the scan. The digital signature is obtained by applying the rule: a k (i)&gt;0 maps onto binary ‘1’ and a k (i)&lt;=0 maps onto binary ‘0’. The digitised data set is defined as d k (i) where i runs from 1 to N. The signature of the article may incorporate further components in addition to the digitised signature of the intensity data just described. These further optional signature components are now described.  
      Step S 6  is an optional step in which a smaller ‘thumbnail’ digital signature is created. This is done either by averaging together adjacent groups of m readings, or more preferably by picking every cth data point, where c is the compression factor of the thumbnail. The latter is preferred since averaging may disproportionately amplify noise. The same digitisation rule used in Step S 5  is then applied to the reduced data set. The thumbnail digitisation is defined as t k (i) where i runs 1 to N/c and c is the compression factor.  
      Step S 7  is an optional step applicable when multiple detector channels exist. The additional component is a cross-correlation component calculated between the intensity data obtained from different ones of the photodetectors. With 2 channels there is one possible cross-correlation coefficient, with 3 channels up to 3, and with 4 channels up to 6 etc. The cross-correlation coefficients are useful, since it has been found that they are good indicators of material type. For example, for a particular type of document, such as a passport of a given type, or laser printer paper, the cross-correlation coefficients always appear to lie in predictable ranges. A normalised cross-correlation can be calculated between a k (i) and a l (i), where k≠l and k,l vary across all of the photodetector channel numbers. The normalised cross-correlation function Γ is defined as  
         Γ   ⁡     (     k   ,   l     )       =         ∑     i   =   1     N     ⁢         a   k     ⁡     (   i   )       ⁢       a   l     ⁡     (   i   )                 (       ∑     i   =   1     N     ⁢         a   k     ⁡     (   i   )       2       )     ⁢     (       ∑     i   =   1     N     ⁢         a   l     ⁡     (   i   )       2       )               
 
      Another aspect of the cross-correlation function that can be stored for use in later verification is the width of the peak in the cross-correlation function, for example the full width half maximum (FWHM). The use of the cross-correlation coefficients in verification processing is described further below.  
      Step S 8  is another optional step which is to compute a simple intensity average value indicative of the signal intensity distribution. This may be an overall average of each of the mean values for the different detectors or an average for each detector, such as a root mean square (rms) value of a k (i). If the detectors are arranged in pairs either side of normal incidence as in the reader described above, an average for each pair of detectors may be used. The intensity value has been found to be a good crude filter for material type, since it is a simple indication of overall reflectivity and roughness of the sample. For example, one can use as the intensity value the unnormalised rms value after removal of the average value, i.e. the DC background.  
      The signature data obtained from scanning an article can be compared against records held in a signature database for verification purposes and/or written to the database to add a new record of the signature to extend the existing database.  
      A new database record will include the digital signature obtained in Step S 5 . This can optionally be supplemented by one or more of its smaller thumbnail version obtained in Step S 6  for each photodetector channel, the cross-correlation coefficients obtained in Step S 7  and the average value(s) obtained in Step S 8 . Alternatively, the thumbnails may be stored on a separate database of their own optimised for rapid searching, and the rest of the data (including the thumbnails) on a main database.  
       FIG. 11  is a flow diagram showing how a signature of an article obtained from a scan can be verified against a signature database.  
      In a simple implementation, the database could simply be searched to find a match based on the full set of signature data. However, to speed up the verification process, the process can use the smaller thumbnails and pre-screening based on the computed average values and cross-correlation coefficients as now described.  
      Verification Step V 1  is the first step of the verification process, which is to scan an article according to the process described above, i.e. to perform Scan Steps S 1  to S 8 .  
      Verification Step V 2  takes each of the thumbnail entries and evaluates the number of matching bits between it and t k (i+j), where j is a bit offset which is varied to compensate for errors in placement of the scanned area. The value of j is determined and then the thumbnail entry which gives the maximum number of matching bits. This is the ‘hit’ used for further processing.  
      Verification Step V 3  is an optional pre-screening test that is performed before analysing the full digital signature stored for the record against the scanned digital signature. In this pre-screen, the rms values obtained in Scan Step S 8  are compared against the corresponding stored values in the database record of the hit. The ‘hit’ is rejected from further processing if the respective average values do not agree within a predefined range. The article is then rejected as non-verified (i.e. jump to Verification Step V 6  and issue fail result).  
      Verification Step V 4  is a further optional pre-screening test that is performed before analysing the full digital signature. In this pre-screen, the cross-correlation coefficients obtained in Scan Step S 7  are compared against the corresponding stored values in the database record of the hit. The ‘hit’ is rejected from further processing if the respective cross-correlation coefficients do not agree within a predefined range. The article is then rejected as non-verified (i.e. jump to Verification Step V 6  and issue fail result).  
      Another check using the cross-correlation coefficients that could be performed in Verification Step V 4  is to check the width of the peak in the cross-correlation function, where the cross-correlation function is evaluated by comparing the value stored from the original scan in Scan Step S 7  above and the re-scanned value:  
           Γ     k   ,   l       ⁡     (   j   )       =         ∑     i   =   1     N     ⁢         a   k     ⁡     (   i   )       ⁢       a   l     ⁡     (     i   +   j     )                 (       ∑     i   =   1     N     ⁢         a   k     ⁡     (   i   )       2       )     ⁢     (       ∑     i   =   1     N     ⁢         a   l     ⁡     (   i   )       2       )               
 
      If the width of the re-scanned peak is significantly higher than the width of the original scan, this may be taken as an indicator that the re-scanned article has been tampered with or is otherwise suspicious. For example, this check should beat a fraudster who attempts to fool the system by printing a bar code or other pattern with the same intensity variations that are expected by the photodetectors from the surface being scanned.  
      Verification Step V 5  is the main comparison between the scanned digital signature obtained in Scan Step S 5  and the corresponding stored values in the database record of the hit. The full stored digitised signature, d k   db (i) is split into n blocks of q adjacent bits on k detector channels, i.e. there are qk bits per block. A typical value for q is 4 and a typical value for k is 4, making typically 16 bits per block. The qk bits are then matched against the qk corresponding bits in the stored digital signature d k   db (i+j). If the number of matching bits within the block is greater or equal to some pre-defined threshold z thresh , then the number of matching blocks is incremented. A typical value for z thresh  is 13. This is repeated for all n blocks. This whole process is repeated for different offset values of j, to compensate for errors in placement of the scanned area, until a maximum number of matching blocks is found. Defining M as the maximum number of matching blocks, the probability of an accidental match is calculated by evaluating:  
         p   ⁡     (   M   )       =       ∑     w   =     n   -   M       n     ⁢             s   w     (     1   -   s     )       n   -   w       w   n     ⁢   C           
 
      where s is the probability of an accidental match between any two blocks (which in turn depends upon the chosen value of z threshold ), M is the number of matching blocks and p(M) is the probability of M or more blocks matching accidentally. The value of s is determined by comparing blocks within the data base from scans of different objects of similar materials, e.g. a number of scans of paper documents etc. For the case of q=4, k=4 and z threshold =13, we typical value of s is 0.1. If the qk bits were entirely independent, then probability theory would give s=0.01 for z threshold =13. The fact that a higher value is found empirically is because of correlations between the k detector channels and also correlations between adjacent bits in the block due to a finite laser spot width. A typical scan of a piece of paper yields around 314 matching blocks out of a total number of 510 blocks, when compared against the data base entry for that piece of paper. Setting M=314, n=510, s=0.1 for the above equation gives a probability of an accidental match of 10 −177 .  
      Verification Step V 6  issues a result of the verification process. The probability result obtained in Verification Step V 5  may be used in a pass/fail test in which the benchmark is a pre-defined probability threshold. In this case the probability threshold may be set at a level by the system, or may be a variable parameter set at a level chosen by the user. Alternatively, the probability result may be output to the user as a confidence level, either in raw form as the probability itself, or in a modified form using relative terms (e.g. no match/poor match/good match/excellent match) or other classification.  
      It will be appreciated that many variations are possible. For example, instead of treating the cross-correlation coefficients as a pre-screen component, they could be treated together with the digitised intensity data as part of the main signature. For example the cross-correlation coefficients could be digitised and added to the digitised intensity data. The cross-correlation coefficients could also be digitised on their own and used to generate bit strings or the like which could then be searched in the same way as described above for the thumbnails of the digitised intensity data in order to find the hits.  
      Thus there have now been described a number of examples arrangements for scanning an article to obtain a signature based upon intrinsic properties of that article. There have also been described examples of how that signature can be generated from the data collected during the scan, and how the signature can be compared to a later scan from the same or a different article to provide a measure of how likely it is that the same article has been scanned in the later scan.  
      Such a system has many applications, amongst which are security and confidence screening of items for fraud prevention and item traceability.  
      In some examples, the method for extracting a signature from a scanned article can be optimised to provide reliable recognition of an article despite deformations to that article caused by, for example, stretching or shrinkage. Such stretching or shrinkage of an article may be caused by, for example, water damage to a paper or cardboard based article.  
      Also, an article may appear to a scanner to be stretched or shrunk if the relative speed of the article to the sensors in the scanner is non-linear. This may occur if, for example the article is being moved along a conveyor system, or if the article is being moved through a scanner by a human holding the article. An example of a likely scenario for this to occur is where a human scans, for example, a bank card using a scanner such as that described with reference to  FIGS. 6A, 6B  and  6 C above.  
      As described above, where a scanner is based upon a scan head which moves within the scanner unit relative to an article held stationary against or in the scanner, then linearisation guidance can be provided by the optional distance marks  28  to address any non-linearities in the motion of the scan head. Where the article is moved by a human, these non-linearities can be greatly exaggerated  
      To address recognition problems which could be caused by these non-linear effects, it is possible to adjust the analysis phase of a scan of an article. Thus a modified validation procedure will now be described with reference to  FIG. 12 . The process implemented in this example uses a block-wise analysis of the data to address the non-linearities.  
      The process carried out in accordance with  FIG. 12 , can include some or all of the steps of smoothing and differentiating the data, computing and subtracting the mean, and digitisation for obtaining the signature and thumbnail described with reference to  FIG. 10 , but are not shown in  FIG. 12  so as not to obscure the content of that figure.  
      As shown in  FIG. 1 , the scanning process for a validation scan using a block-wise analysis starts at step S 21  by performing a scan of the article to acquire the date describing the intrinsic properties of the article. This scanned data is then divided into contiguous blocks (which can be performed before or after digitisation and any smoothing/differentiation or the like) at step S 22 . In one example, a scan length of 54 mm is divided into eight equal length blocks. Each block therefore represents a subsection of scanned area of the scanned article.  
      For each of the blocks, a cross-correlation is performed against the equivalent block for each stored signature with which it is intended that article be compared at step S 23 . This can be performed using a thumbnail approach with one thumbnail for each block. The results of these cross-correlation calculations are then analysed to identify the location of the cross-correlation peak. The location of the cross-correlation peak is then compared at step S 24  to the expected location of the peak for the case were a perfectly linear relationship to exist between the original and later scans of the article.  
      This relationship can be represented graphically as shown in  FIGS. 13A, 13B  and  13 C. In the example of  FIG. 13A , the cross-correlation peaks are exactly where expected, such that the motion of the scan head relative to the article has been perfectly linear and the article has not experienced stretch or shrinkage. Thus a plot of actual peak positions against expected peak results in a straight line which passes through the origin and has a gradient of 1.  
      In the example of  FIG. 13B , the cross-correlation peaks are closer together than expected, such that the gradient of a line of best fit is less than one. Thus the article has shrunk relative to its physical characteristics upon initial scanning. Also, the best fit line does not pass through the origin of the plot. Thus the article is shifted relative to the scan head compared to its position upon initial scanning.  
      In the example of  FIG. 13C , the cross correlation peaks do not form a straight line. In this example, they approximately fit to a curve representing a y 2  function. Thus the movement of the article relative to the scan head has slowed during the scan. Also, as the best fit curve does not cross the origin, it is clear that the article is shifted relative to its position upon initial scanning.  
      A variety of functions can be test-fitted to the plot of points of the cross-correlation peaks to find a best-fitting function. Thus curves to account for stretch, shrinkage, misalignment, acceleration, deceleration, and combinations thereof can be used.  
      Once a best-fitting function has been identified at step S 25 , a set of change parameters can be determined which represent how much each cross-correlation peak is shifted from its expected position at step S 26 . These compensation parameters can then, at step S 27 , be applied to the data from the scan taken at step S 21  in order substantially to reverse the effects of the shrinkage, stretch, misalignment, acceleration or deceleration on the data from the scan. As will be appreciated, the better the best-fit function obtained at step S 25  fits the scan data, the better the compensation effect will be.  
      The compensated scan data is then broken into contiguous blocks at step S 28  as in step S 22 . The blocks are then individually cross-correlated with the respective blocks of data from the stored signature at step S 29  to obtain the cross-correlation coefficients. This time the magnitude of the cross-correlation peaks are analysed to determine the uniqueness factor at step S 29 . Thus it can be determined whether the scanned article is the same as the article which was scanned when the stored signature was created.  
      Accordingly, there has now been described an example of a method for compensating for physical deformations in a scanned article, and for non-linearities in the motion of the article relative to the scanner. Using this method, a scanned article can be checked against a stored signature for that article obtained from an earlier scan of the article to determine with a high level of certainty whether or not the same article is present at the later scan. Thereby an article constructed from easily distorted material can be reliably recognised. Also, a scanner where the motion of the scanner relative to the article may be non-linear can be used, thereby allowing the use of a low-cost scanner without motion control elements.  
      In some scanner apparatuses, it is also possible that it may be difficult to determine where a scanned region starts and finishes. Of the examples discussed above, this is most problematic for the example of  FIG. 6B , where an article to be scanned passes through a slot, such that the scan head may “see” more of an article than the intended scan area. One approach to addressing this difficulty would be to define the scan area as starting at the edge of the article. As the data received at the scan head will undergo a clear step change when an article is passed though what was previously free space, the data retrieved at the scan head can be used to determine where the scan starts.  
      In this example, the scan head is operational prior to the application of the article to the scanner. Thus initially the scan head receives data corresponding to the unoccupied space in front of the scan head. As the article is passed in front of the scan head, the data received by the scan head immediately changes to be data describing the article. Thus the data can be monitored to determine where the article starts and all data prior to that can be discarded. The position and length of the scan area relative to the article leading edge can be determined in a number of ways. The simplest is to make the scan area the entire length of the article, such that the end can be detected by the scan head again picking up data corresponding to free space. Another method is to start and/or stop the recorded data a predetermined number of scan readings from the leading edge. Assuming that the article always moves past the scan head at approximately the same speed, this would result in a consistent scan area. Another alternative is to use actual marks on the article to start and stop the scan region, although this may require more work, in terms of data processing, to determine which captured data corresponds to the scan area and which data can be discarded.  
      Thus there has now been described an number of techniques for scanning an item to gather data based on an intrinsic property of the article, compensating if necessary for damage to the article or non-linearities in the scanning process, and comparing the article to a stored signature based upon a previous scan of an article to determine whether the same article is present for both scans.  
      Another characteristic of an article which can be detected using a block-wise analysis of a signature generated based upon an intrinsic property of that article is that of localised damage to the article. For example, such a technique can be used to detect modifications to an article made after an initial record scan.  
      For example, many documents, such as passports, ID cards and driving licenses, include photographs of the bearer. If an authenticity scan of such an article includes a portion of the photograph, then any alteration made to that photograph will be detected. Taking an arbitrary example of splitting a signature into 10 blocks, three of those blocks may cover a photograph on a document and the other seven cover another part of the document, such as a background material. If the photograph is replaced, then a subsequent rescan of the document can be expected to provide a good match for the seven blocks where no modification has occurred, but the replaced photograph will provide a very poor match. By knowing that those three blocks correspond to the photograph, the fact that all three provide a very poor match can be used to automatically fail the validation of the document, regardless of the average score over the whole signature.  
      Also, many documents include written indications of one or more persons, for example the name of a person identified by a passport, driving license or identity card, or the name of a bank account holder. Many documents also include a place where written signature of a bearer or certifier is applied. Using a block-wise analysis of a signature obtained therefrom for validation can detect a modification to alter a name or other important word or number printed or written onto a document. A block which corresponds to the position of an altered printing or writing can be expected to produce a much lower quality match than blocks where no modification has taken place. Thus a modified name or written signature can be detected and the document failed in a validation test even if the overall match of the document is sufficiently high to obtain a pass result.  
      An example of an identity card  300  is shown in  FIG. 300 . The identity card  300  includes a printed bearer name  302 , a photograph of the bearer  304 , a signature of the bearer  306  (which may be written onto the card, or printed from a scan of a written signature or a signature captured electronically), and a printed card number  308 . In order to protect against fraudulent alteration to the identity card, a scan area for generating a signature based upon an intrinsic property of the card can include one or more of those elements. Various example scan areas are marked in  FIG. 15  to illustrate the possibilities. Example scan area  321  includes part of the printed name  302  and part of the photograph  304 . Example scan area  322  includes part of the printed name. Example scan area  323  includes part of the signature  306 . Example scan area  324  includes part of the card number  308 .  
      The area and elements selected for the scan area can depend upon a number of factors, including the element of the document which it is most likely that a fraudster would attempt to alter. For example, for any document including a photograph the most likely alteration target will usually be the photograph as this visually identifies the bearer. Thus a scan area for such a document might beneficially be selected to include a portion of the photograph. Another element which may be subjected to fraudulent modification is the bearer&#39;s signature, as it is easy for a person to pretend to have a name other than their own, but harder to copy another person&#39;s signature. Therefore for signed documents, particularly those not including a photograph, a scan area may beneficially include a portion of a signature on the document.  
      In the general case therefore, it can be seen that a test for authenticity of an article can comprise a test for a sufficiently high quality match between a verification signature and a record signature for the whole of the signature, and a sufficiently high match over at least selected blocks of the signatures. Thus regions important to the assessing the authenticity of an article can be selected as being critical to achieving a positive authenticity result.  
      In some examples, blocks other than those selected as critical blocks may be allowed to present a poor match result. Thus a document may be accepted as authentic despite being torn or otherwise damaged in parts, so long as the critical blocks provide a good match and the signature as a whole provides a good match.  
      Thus there have now been described a number of examples of a system, method and apparatus for identifying localised damage to an article, and for rejecting an inauthentic an article with localised damage or alteration in predetermined regions thereof. Damage or alteration in other regions may be ignored, thereby allowing the document to be recognised as authentic.  
      When using a biometric technique such as the identity technique described with reference to FIGS.  1  to  14  above for the verification of the authenticity or identity of an article, difficulties can arise with the reproducibility of signatures based upon biometric characteristics. In particular, as well as the inherent tendency for a biometric signature generation system to return slightly different results in each signature generated from an article, where an article is subjected to a signature generation process at different signature generation apparatuses and at different times there is the possibility that a slightly different portion of the article is presented on each occasion, making reliable verification more difficult.  
      Examples of systems, methods and apparatuses for addressing these difficulties will now be described. First, with reference to  FIG. 15 , a multi-scan head signature generation apparatus for database creation will be described.  
      As shown in  FIG. 15 , a reader unit  100  can include two optic subassemblies  20 , each operable to create a signature for an article presented in a reading volume  102  of the reader unit. Thus an item presented for scanning to create a signature for recording of the item in an item database against which the item can later be verified, can be scanned twice, to create two signatures, spatially offset from one another by a likely alignment error amount. Thus a later scan of the item for identification or authenticity verification can be matched against both stored signatures. In some examples, a match against one of the two stored signatures can be considered as a successful match.  
      In some examples, further read heads can be used, such that three, four or more signatures are created for each item. Each scan head can be offset from the others in order to provide signatures from positions adjacent the intended scan location. Thus greater robustness to article misalignment on verification scanning can be provided.  
      The offset between scan heads can be selected dependent upon factors such as a width of scanned portion of the article, size of scanned are relative to the total article size, likely misalignment amount during verification scanning, and article material.  
      Thus there has now been described a system for scanning an article to create a signature database against which an article can be checked to verify the identity and/or authenticity of the article.  
      An example of another system for providing multiple signatures in an article database will now be describe with reference to  FIG. 16 .  
      As shown in  FIG. 16 , a reader unit  100 ′ can have a single optic subassembly  20  and an alignment adjustment unit  104 . In use, the alignment adjustment unit  104  can alter the alignment of the optics subassembly  20  relative to the reading volume  102  of the reader unit. Thus an article placed in the reading volume can be scanned multiple times by the optics subassembly  20  in different positions so as to create multiple signatures for the article. In the present example, the alignment adjustment unit  104  can adjust the optics subassembly to read from two different locations. Thus a later scan of the item for identification or authenticity verification can be matched against both stored signatures. In some examples, a match against one of the two stored signatures can be considered as a successful match.  
      In some examples, further read head positions can be used, such that three, four or more signatures are created for each item. Each scan head position can be offset from the others in order to provide signatures from positions adjacent the intended scan location. Thus greater robustness to article misalignment on verification scanning can be provided.  
      The offset between scan head positions can be selected dependent upon factors such as a width of scanned portion of the article, size of scanned are relative to the total article size, likely misalignment amount during verification scanning, and article material.  
      Thus there has now been described another example of a system for scanning an article to create a signature database against which an article can be checked to verify the identity and/or authenticity of the article.  
      Although it has been described above that a scanner used for record scanning (i.e. scanning of articles to create reference signatures against which the article can later be validated) can use multiple scan heads and/or scan head positions to create multiple signatures for an article, it is also possible to use a similar system for later validation scanning.  
      For example, a scanner for use in a validation scan may have multiple read heads to enable multiple validation scan signatures to be generated. Each of these multiple signatures can be compared to a database of recorded signatures, which may itself contain multiple signatures for each recorded item. Due to the fact that, although the different signatures for each item may vary these signatures will all still be extremely different to any signatures for any other items, a match between any one record scan signature and any one validation scan signature should provide sufficient confidence in the identity and/or authenticity of an item.  
      A multiple read head validation scanner can be arranged much as described with reference to  FIG. 15  above. Likewise, a multiple read head position validation scanner can be arranged much as described with reference to  FIG. 16  above. Also, for both the record and validation scanners, a system of combined multiple scan heads and multiple scan head positions per scan head can be combined into a single device.  
      As discussed above, key distribution for encryption is a field in which reliable and secure provision for the distribution is greatly desirable. In the following examples, there will be discussed systems, apparatus and methods for secure distribution of encryption key as well as examples for the secure distribution of data other than encryption keys, such other data may include identification information such as logon information, and database query information.  
      With reference to  FIG. 17 , an encryption key  200  can be packaged for secure transmission such that only the holder of a unique security token can retrieve the key. To achieve this, in the present example, error correction bits are added to the key at  202 . In some examples, additional random data may be added to the key before the error correction bits are added. Then, a signature  204  calculated from a scan of a security token, for example as discussed with reference to FIGS.  1  to  16  above, is exclusive-ORed  206  with the key plus error correction data  202 . This exclusive OR operation is performed on a bitwise basis to create a packaged key  208 .  
      Thus the encryption key has been packaged in such a manner than an authorised recipient can retrieve it, but such that a third party intercepting the packaged key cannot obtain the key therefrom.  
      With reference to  FIG. 18 , a method for unpacking the key by an authorised recipient will now be described. The packaged key  208  is bitwise exclusive-ORed  214  with a signature  212  calculated from a scan of the security token, for example as discussed with reference to FIGS.  1  to  16  above, to obtain the encryption key with the error correction bits  216 . This recovered encryption key with error correction bits may include errors relative to the original encryption key with error correction bits  202  as the signatures used for packaging and unpacking may not be identical, even though they are made from the same security token using the same method. Thus the error correction bits are used to correct  218  any such errors which may have occurred in the key, so as to reproduce the encryption key  220  which is identical to the encryption key  100  originally packaged for transmission.  
      The error correction coding strength and system used can be selected based upon an expected error rate in the security token signatures.  
      In examples where additional random data is added to the key, or where the key inherently contains redundant information, the operation of the error correction coding can be enhanced.  
      The error correction coding and redundant information allow a biometric type signature, such as one generated as set out with reference to any of FIGS.  1  to  16  above, to be used with a non-error tolerant system such as an encryption key. It is a fundamental behaviour of biometric based identification systems that the probability of the same item producing exactly the same biometric signature more than once, even when the same procedure is used on the same item, is extremely small. Thus the differences between two biometric signatures of the same item can be allowed for to create an error free system for securing an error intolerant system.  
      In some examples, the packaged key may be transmitted alone such that the key is distributed as a stand-alone item. This could be used for distribution of a key from a public/private key pair in a manner which enables the recipient to be certain of the originator of the key. In other examples, the packaged key may be transmitted with data which has been encrypted using the key, such that the recipient of the data is provided with the decryption key for use in decrypting that data. Such systems allow the easy use of short usage life encryption keys, with each key being used for as little as one data packet before being discarded in favour of a new key. Such frequent changes in encryption keys provide no inconvenience to a data recipient in such cases as the security token allows the new keys to be accessed and used without needing user input for tracking of new keys.  
      In some examples, either the signature used for packaging or the signature used for unpacking may be a previously created signature stored by the packaging or unpacking entity. In some examples, an entity may maintain a large database of signatures, the database containing signatures relating to many different security tokens. Thus, for example, a financial services entity (such as a bank) may store signatures for security tokens of many customers, allowing the entity to enter into secure encrypted communications with its customers on an individual basis.  
      In the system, method and apparatus of the present examples any item can be used as the security token, in particular, the token can be primarily two-dimensional and can be optically opaque or translucent. The use of such articles is set out in more detail with reference to FIGS.  1  to  16  above.  
      The security token used for providing the secure access to the key can be any item from which it is possible to create the necessary signature. For example an item which is normally carried such as a bank, credit or loyalty card could be used as an access token, regardless of whether the information related to information about that bank or loyalty scheme. Alternatively, a completely non-obvious access token could be used. Examples could include a business card or other similar item. Use of such a non-obvious access token would reduce the chances of a person stealing or finding the access token from using it to gain access to the owner&#39;s data. Thereby the “steal me” problem commonly associated with obviously important items and documents (such as bank cards and packages marked “private and confidential”) can be avoided.  
      Thus encryption keys can be securely distributed to allow an intended recipient to extract the key for use, while any third party receiving the key cannot obtain the actual key.  
      In some examples a database access request may be made, using a database logon as necessary and a suitable query. The response from the database may be transmitted using a packaged key with appended encrypted data as described above. In one example, a signature based upon an intrinsic characteristic of a database access token may be used as the database logon and/or query. The submitted signature can be used as the logon and search query by associating each data record in the database with a signature, and making the signature a searchable field. In some examples, the signature may be on the only searchable field with the possible exceptions of systems administrator access, regulatory inspection access and legal or criminal investigation access. In addition or alternatively, the signature submitted for search and/or logon purposes may in fact be used to package a database access key much as outlined above for packaging of an encryption key. The access key could then be recovered error free from the packaged key using a copy of the signature stored for an access mechanism for the database. The resulting database record could then be returned using the signature of the security token to package an encryption key for decrypting the returned data.  
      In some examples, the database access token and the security token could be the same physical article. Different signatures could be generated from the article by scanning different areas of the article, and/or by scanning at different resolutions.  
      Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications as well as their equivalents.