Classifications

• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
  • G07D7/12—Visible light, infrared or ultraviolet radiation
  • G07D7/121—Apparatus characterised by sensor details
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/003—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using security elements
  • G07D7/0032—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using security elements using holograms
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/004—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using digital security elements, e.g. information coded on a magnetic thread or strip
  • G07D7/0043—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using digital security elements, e.g. information coded on a magnetic thread or strip using barcodes
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
  • G03H2001/0454—Arrangement for recovering hologram complex amplitude
  • G03H2001/0458—Temporal or spatial phase shifting, e.g. parallel phase shifting method

Definitions

• the present invention relates to a method of authentication and optical identification of objects and to a device for implementing this method.
• a mark that is difficult to reproduce or falsify such as a holographic label
• one can structure in a particular way its support material for example, or alternatively, one can include in the material of one of the parts of the object particles or components which can only be detected by physical observation using special devices.
• the subject of the present invention is a method of authenticating and / or identifying objects which does not require any modification of these objects, which makes it possible to authenticate them without fail, which makes it possible to easily recognize counterfeit objects, and which either easy to set up.
• the present invention also relates to an authentication and or identification device for objects which is easy to make and use, which can be easily adapted to any kind of object and which is as inexpensive as possible.
• the method according to the invention consists in illuminating in coherent light an at least partially diffusing surface in volume of control objects under precise lighting conditions, in recording the speckle patterns thus obtained for different nominal values of illumination parameters. and in a range of values around these nominal values, then, when checking other objects or these same objects, to illuminate these objects under the same nominal conditions and to compare each time the figure of scab marks thus obtained with those who have been registered and to retain the objects if their scab figure corresponds to one of those which have been registered.
• the device according to the invention comprises an optical recording device with laser source, a storage device and an optical reading device with laser source, parameters of these optical devices being modifiable.
• the modifiable parameters of the optical devices are at least one of the following parameters: wavelength of the laser source, direction of emission of the laser beam, focusing of the laser beam, position of the source laser, tilt and position of the object relative to the laser beam.
• FIGS. 1 and 2 are block diagrams of two different embodiments of the optical device for reading the authentication and identification device according to the invention
• - Figure 3 is a block diagram of an embodiment of the optical recording device of the authentication and identification device according to the invention
• - Figure 4 is a simplified view of a spectral range d '' images used to constitute the references during the recording of scab figures according to the method of the invention
• - Figure 5 is a simplified block diagram of an embodiment of an optical device according to the invention for recording references to electronic holography.
• the invention is aimed both at authentication and at identifying objects with the same recording and reading devices. Thereafter, for simplification purposes only authentication will be involved, it being understood that the same apparatus and methods apply to identification.
• the reading device If the device used for checking (here called the reading device) is the same as the one used for recording, one can hope for good reproducibility. On the other hand, if one wants to develop a system comprising several readers of low cost, it is necessary to solve this problem.
• the complexity of the scab structure and its sensitivity to the various observation parameters depend on the characteristics of the scattering medium: its mean scattering wavelength, its abso ⁇ tion, the number and the geometric characteristics of the inhomogeneities.
• the invention provides, by construction of the reading system, for reducing the number of parameters on which the result depends.
• an optical configuration tolerant to tilt is advantageously chosen.
• the first of these characteristics consists in recording the speckle patterns for the different values that these uncontrolled parameters can take, for example when the wavelength of the coherent beam of illumination can differ from one reader to another, the speckle patterns of an object are recorded for the various wavelengths possible in reading.
• This process requires a complex and expensive recording system, but the recording operation is unique, or carried out with a small number of recording systems, while the readers are generally numerous and must be inexpensive.
• scab figures cannot be saved for a large number of parameter values, as the reference database for a given object would increase rapidly and could lead to a reduction in performance during the recognition step.
• the second of these characteristics consists, in the reading phase, in varying the parameter considered within the range of admissible values.
• the value of the current of the read laser diode is a small range of wavelengths.
• the parameters which the invention provides for varying the value there are in particular: the focusing of the reading beam, the position of the illumination source, the inclination of the object relative to this beam.
• the system is made interactive by verifying that, for a given parameter, drawn randomly in the range of authorized values (for example in the case of a particular position of the reading system in relation to the object), the signal observed is indeed that which is expected. It is thus possible to choose the level of security that one wishes: one can privilege with the same system the speed of identification or authentication, or the security by multiplying the number of verifications. This characteristic makes the process of the invention both more robust and more difficult to violate.
• Recognition performance is linked to the amount of information collected during the acquisition stage.
• This quantity I of information can be defined by the relation:
• I Log (posterior probability / a priori probability) the posterior probability being the probability that the recognized object is the right one, taking into account the observation made, and the a priori probability is the probability that the observation that we made it happen.
• the comparison method of the invention takes into account the nature of the acquisitions which are in the form of images.
• a classic method of image comparison is the correlation of raw images or those from pre-processing intended to normalize them.
• a correlation is a global comparison of the images, and it is decided that two images are identical if the maximum correlation is greater than a given threshold.
• the choice of the threshold has an important impact on the a priori probability: for example if we work on binary signals of length 1000 bits and we set the threshold at 0.5, the a priori probability goes from 10 ⁇ -301 to 10 ⁇ -58. In practice, and for reasons of robustness, it is often necessary to set the decision threshold at a significantly lower value, ie to tolerate a much higher percentage of error.
• This reader 1 comprises a laser source 2, for example a single-mode laser diode, considered as a point source 2a, followed by a lens 3 at the image focal point 4 from which the image of the source 2a is formed.
• Focus 4 coincides with the target focus a second lens 5 of short focal length (for example 4 mm) whose optical axis is pe ⁇ endicular to that of the lens 3.
• the image focal point of the lens 5 coincides with the surface of the object 6 to be examined.
• the lens 5 is immediately followed by a diaphragm 7.
• the focal point 4 is brought to the oblique separation face of a cube 8 for polarization separation. Pe ⁇ endicular to the optical axis of the lens 5, opposite the object 6 relative to the cube 8, there is a detector 9.
• the lens 3 forms an image of the source point 2a at the focus object of the lens 5.
• the beam 10 of illumination of the object 6 is collimated, and its section is determined by the diaphragm 7.
• the lens 5 forms an image of the lit area of the object 6 on the detector 9.
• the cube 8 reflects on the go the polarized illumination beam towards the object 6, while it does not let pass (without reflecting it ) in the opposite direction as the polarized beam orthogonal to the first.
• the specular reflection of the object 6 is eliminated or greatly reduced.
• the digital aperture of the reading system 1 and the value of its optical magnification are chosen so that the grain size of the speckles is greater than that of the pixels of the detector 9, so as to avoid aliasing phenomena which would harm the quality of recognition.
• an object field having dimensions of the order of 500 ⁇ m x 500 ⁇ m. If the useful surface of the detector 9 is 5mm x 5mm, the optical magnification can be 10 times. If the detector 9 has a matrix of 256 x 256 pixels, it will only be possible to sample correctly 10.e4 grains of speckles.
• the resolution of the reading system is deliberately limited to 5 ⁇ m in the object plane, for example by limiting the numerical aperture to 0.1 using the diaphragm 7.
• the reader 1 also includes precise positioning means (not shown) of the object 6 as well as calculation means (not shown) making it possible to compare the digital image observed with the expected image (recorded) for the object to be check.
• the system 1 also includes means for reading (not shown) the information contained on the surface or inside of the object 6 (magnetic strip, electronic chip, optical storage area, bar code, etc.). .).
• FIG. 2 shows another embodiment 10 of the optical device of the reading system of the invention. In this figure, elements similar to those of FIG. 1 are given the same reference numbers. The main difference compared to the device of FIG.
• the laser source 2 directly illuminates the oblique face of the cube 8, and it is located at the focal point of the lens 3 (taking into account the reflection of the laser beam on the oblique face of the cube 8).
• Figure 3 an embodiment of the scab pattern recording system according to the invention. In general, the recording system is similar to the playback system.
• the device 11 of FIG. 3 comprises the same optical imaging device as that of FIG. 2, namely the lenses 3 and 5 with optical optical axes combined and placed on either side of the separating cube 8.
• the laser source 2 is placed at the object focus of the lens 3.
• the diaphragm 7 is placed immediately after (in the forward direction of the beam from the laser source) the lens 3.
• the object 6a (we seek to check whether it is actually authentic (i.e. object 6 itself, which was used to build the database) is placed in the same way as object 6.
• FIG. 3 shows the same optical imaging device as that of FIG. 2, namely the lenses 3 and 5 with optical optical axes combined and placed on either side of the separating cube 8.
• the laser source 2 is placed at the object focus of the lens 3.
• the diaphragm 7 is placed immediately after (in the forward direction of the beam from the laser source) the lens 3.
• the object 6a (we seek to check whether it is actually authentic (i.e. object 6 itself, which was used to build the database) is
• the 3 shows an actuator 12 which is used to vary very finely (by a few microns or tens of microns, for example) the focusing distance of the laser beam on the object 6a, by varying, for example, the position of the lens 3. It is also possible to vary the aperture of the diaphragm 7. Of course, other means (not shown) make it possible to vary the other critical parameters of the system recording (laser wavelength, etc., as specified above).
• the images recorded in the database can be raw images supplied by the detector of the recording system.
• the invention provides for recording pre-processed images, preferably in compressed form, in particular when the database must include a large number of images. Pretreatment can be done in many ways. Because the Fourier transform of the image (obtained for example by FFT) is well suited to recognition in reading, it is one of the preferred preprocessing methods of the invention. In order to normalize the reference image thus obtained, it is divided by its module, that is to say that only its phase information is kept, which amounts to carrying out an operation of "whitening" the spectrum. of the image.
• the values corresponding to the low spatial frequencies are suppressed, which include terms related to the object (at medium reflectivity), to the illumination (to avoid inhomogeneities of the illumination beam), and which may also contain aliasing residues.
• the values corresponding to the high spatial frequencies, whose signal to noise ratio is lower, are also suppressed.
• the retained values are coded with as few bits as possible, without however reducing the probability of recognition too much. It is necessary to find, according to the level of security sought, and according to the maximum desired volume of the database, a compromise between the number of values retained for each reference and the dynamic of the references.
• FIG. 4 shows an example of the spectral domain chosen to constitute a reference database. In this FIG.
• the coordinate axes are graduated in normalized values of spatial frequencies of the speckle figures, in x and in y.
• Contour 13 defined for frequencies lower than half of the normalized spatial frequency, includes all the spatial frequencies of the image, and delimits a closed surface 14 (in gray) inside which one has drawn an example of spectral domain retained 15 (hatched) contained in the surface 14.
• Other image transformations leading to a reduction in the size of the database with a reduced loss of information can be implemented within the framework of the invention, by example the transforms in wavy heads or the transforms in cosine. As in the conventional image compression methods, only a certain number of the most significant transform coefficients are retained.
• the method of the invention proceeds as follows for local authentication.
• the reading system has the public key which allows it to read and decrypt the signature of the speckle image on the card.
• a comparison is made between the optical signature observed and the signature stored on the card. This comparison can be made according to a conventional method called “pattern matching”, for example by a correlation between the observed image and the reference image, as specified above.
• the comparison operation essentially consists in taking the Fourier transform of the observed image and to make the product of the spectral components retained by those of the reference. The result of the operation is then compared to a threshold to decide on authenticity.
• the decision of authenticity is preferably made using a hybrid criterion weighing several results, for example:
• a variant of the authentication method according to the invention consists in practicing authentication on a site remote from the readers, for example at the location of a server connected to the different readers and to a recorder.
• the authentication step is done from the database recorded during the recording step.
• the optical signature of the speckle image and the reference of the object are provided, as well as the parameters of the reader.
• the server makes the comparison between the optical image as read by a reader and the reference image of the object corresponding to the parameters supplied to the server.
• the invention provides for performing, periodically or each time a reader is used, calibrations of the various parameters necessary for authentication, in particular of the critical parameters. These calibrations are done using one or more speckle images of calibration objects.
• the calibration object can be the support of the reading system.
• the parameters of the reader used are determined locally or by the server to which it is connected.
• the authentication is carried out on the basis of an interrogation of a reader.
• the reader in question comprises a focusing lens (lens 5 of the embodiments described above) mounted on actuators allowing displacements in one or two directions from the plane pe ⁇ endicular to the optical axis of the lens.
• actuators allow automatic and precise adjustment of the focus.
• a scab image of the observed area of the object is formed on the two-dimensional sensor of the detector (detector 9).
• the object observed for example an access card to a protected place, is pre-positioned under the lens of the optical reader, thanks to an appropriate mechanical guiding device.
• the speckle image is transmitted to the validation device at the same time as the identification data carried by the card or supplied by the card holder.
• the validation device compares the scab image received with the image corresponding to the reference of the object (stored in the validation device or transmitted from a database). If the object is the one declared, the result of the comparison is positive. If the comparison is based on a correlation, data for positioning the object relative to the sensor are supplied to the validation device. This data is a measure of the positioning error of the object under the sensor. They can be supplied to the object positioning devices to allow correction of the position of the object. In this case, a second measurement, carried out after such a position correction, must improve the quality of recognition and allow the authentication of the object to be practically certain.
• the second measurement gives inconsistent results with those of the first (for example if the new position error found is not close to zero or if the result has not improved significantly), there is a high probability that the object examined is not the correct one.
• the “zero” position having been determined in accordance with the steps set out above, the reader can be asked to position himself on a point whose coordinates will have been drawn at random from a determined set of values. The reader must then be able to provide an image of speckles corresponding to that recorded in the database for these observation coordinates and this object. The probability of false acceptance is thus significantly reduced.
• the coordinates explored can be those of a plane pe ⁇ endicuiaire to the optical axis of the focusing lens (lens 5) or the coordinate along this optical axis (i.e. a translation of the focusing plane parallel to itself, depending on the number of degrees of freedom of said actuators.
• This method of authentication has several advantages. The first is that the system is made more tolerant of positioning errors or deformations of the object.
• the second is that the comparison is made on a larger area of the object, which makes it more difficult to copy, and keeps the system from operating problems related to focal degradation of the object (which can happen with frequently handled objects, which can be scratched)
• the third is that the reader is able to respond to an unpredictable request from the system (which randomly draws the coordinates of the point to be observed), which makes the pir more complex. reading device by a hardware or software device that would respond in its place. In this case, the hacker should have access to all of the data on the surface or in the active volume of the object.
• the focusing device can use an auxiliary beam focused on the surface of the object to be examined.
• the focus error detector can, in this case, be of a known type, such as the astigmatic sensor often used in the read heads of optical discs. However, it may be easier to directly observe the speckle signal used to authenticate the object.
• One possible method consists in placing the objective in its most probable focusing position, in carrying out the comparison with the expected speckle pattern, then in slightly varying this position. The variation in the result of the comparison makes it possible to evaluate the correction to be made to the position of the objective in order to increase the quality of the result, and therefore to approach the position of best focus, which is similar to the gradient method. .
• the optical device was designed so as to produce on the detector an image of the useful area of the object.
• This device can, as a variant, operate if the detector is not in the image plane of the optical device.
• the detector can then be in a conjugate plane of the plane of the pupil of the optical device, which is the plane of Fourier of the illuminated object.
• the spatial filtering of the speckles, respecting Shannon's sampling conditions can be done either by limiting the size of the illumination spot on the object, or by applying a diaphragm on an intermediate image plane.
• the arrangement of the sensor on an “intermediate” plane may represent a better compromise in system design vis-à-vis the adaptation of the grain size of speckles at the spatial resolution of the detector.
• the illumination of the object was considered to be uniform and collimated.
• the system of the invention also works even when these conditions are not met.
• FIG. 5 shows the simplified diagram of a recording device according to the invention, in which the recording is done by an electronic holography process.
• the laser source 17 is placed at the focal point of a collimating lens 18 which is followed by a separating cube 19 of which it illuminates the oblique semi-reflecting face.
• Part of the parallel beam coming from the lens 18 crosses this oblique face and arrives perpendicularly on a mirror 20 driven by a piezoelectric actuator.
• the beam reflected by the mirror 20 arrives on the oblique face of the cube 19, on which it is reflected towards a detector 21.
• the detector 21 therefore receives an illumination consisting of the combination of the reference beam and a beam backscattered by the object 22 (which passes directly through the cube 19).
• several holograms thus obtained are recorded, each time varying the length of the optical path of the reference beam using the actuator of the mirror 20.
• the advantage of this process is to record a holographic image of the object, which makes it possible to recalculate the image as it would be seen by an observation device with characteristics slightly different from the nominal characteristics.
• the illuminated medium of the object is very diffusing, it will still be necessary to record holograms corresponding to the various possible wavelengths for the observation, because, the paths of light being multiple, the field backscattered does not simply depend on the observation wavelength.

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• Physics & Mathematics (AREA)
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• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Collating Specific Patterns (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Holo Graphy (AREA)

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• 2002
  • 2002-12-20 FR FR0216366A patent/FR2849245B1/fr not_active Expired - Fee Related
• 2003
  • 2003-12-10 US US10/539,767 patent/US20060104103A1/en not_active Abandoned
  • 2003-12-10 AU AU2003298351A patent/AU2003298351A1/en not_active Abandoned
  • 2003-12-10 EP EP03796091A patent/EP1573661A1/de not_active Withdrawn
  • 2003-12-10 CN CNA200380109386XA patent/CN1745387A/zh active Pending
  • 2003-12-10 WO PCT/EP2003/050975 patent/WO2004057525A1/fr not_active Application Discontinuation

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