Header. The Covert Diffractive Image A LaserCard Security Feature

Transcription

1 Header The Covert Diffractive Image A LaserCard Security Feature Robert Hazel, Ph.D New Product Engineering Manager, LaserCard Corporation July, N. Shoreline Blvd Mountain View, CA USA tel: fax: sales@lasercard.com Copyright

2 History of Holographic Security Holography was invented in 1947 by Dennis Gabor to improve the resolving power on electron microscopes. The light laser invented by Theodore Maiman in 1960 presented the means for creating the visible holograms we are all familiar with. White light holograms such as the Rainbow Hologram invented by Stephen Benton in 1968 have allowed holograms to be sold to the mass market where they can be viewed in natural light. Also, the advent of inexpensive semiconductor lasers makes inexpensive laser based hologram viewers a practicality. Security holograms first appeared in the mid 1980 s on Visa and MasterCard payment cards. The Visa Dove is perhaps the most widely identifiable of these holograms. Such holograms are now employed to secure a broad range of items. A good survey of the construction and application of credit card security card holograms is presented in the paper Application of Holograms to Credit Cards by Don Tomkins, Kurz Transfer Products, L.P. Most card holographic security features are attached to the card base during the manufacturing personalization process. If the card is in part an optical recording medium then it is possible to record the hologram directly into the medium. A practical implementation of this concept presents a large number of technical and price hurdles especially if the medium is not tailored for holographic recording. A complex optical system is required to record a quality hologram. For security holographic features, the optical recording replication requirement can be eliminated by creating a computer-generated pattern on the master of formatted medium information (the Photomask). This becomes practical if the lithographic process has sub-micron resolution and the formatted medium has good diffraction characteristics (a contoured surface). The resulting embedded security hologram is more secure than the stamped holograms employed on bank cards. In the latter case, a counterfeit label can easily be attached to a card and may pass visual inspection. To counterfeit a hologram which is a part of the card optical medium format, the whole medium must be counterfeited. The LaserCard Covert Diffractive Image is just such a security hologram. It has been mastered onto high security LaserCard Optical Security Media based identification cards since [Note: Another LaserCard optical security feature is the Personalized Embedded Hologram (PEH), which is a facial image and other information about the cardholder laser etched onto the Optical Security Media during personalization. While not a true hologram, the PEH exhibits hologram-like characteristics associated with the diffraction of light, such as changes in appearance and color with viewing angle, when viewed in natural light. For more information, please see The Role of Optical Security Media in Secure Identification by Dr Christopher Dyball, Chief Operating Officer, LaserCard Corporation, which can be downloaded by visiting: LaserCard s Covert Diffractive Image A Security Hologram The Diffractive Image is a formatted, digitally mastered hologram created by a software program. It can be located at one or more positions on a card; in this document the Diffractive Image at each location is referred to as a diffractive element. Usually the diffractive element has a maximum dimension of about 3mm 2. Figure 1 below shows a typical diffractive element on a secure Identity Card. The outline shape of the diffractive element is user defined and may essentially be any graphical design. The shape has no impact on the holographic image produced provided that the laser beam used to recreate the image is largely confined to the area within the element boundary. A diffractive element generates an image when it is illuminated with a collimated laser beam as shown in Figure 1. The Diffractive Image of each card type generates a unique image that is easily identified visually. 2

3 Figure 1 Example of a Diffractive Element Figure 2 Projection of the Diffractive Image The diffracted light behaves as if it is emanating from the pinhole of a pinhole camera as shown in Figure 3. This means that the image can be generated by placing a flat screen in the path of the reflected light. There is no focal plane so the size of the image can be changed simply by moving the screen towards or away from the card. Also, the image can be magnified in one axis only by tilting the screen away from the orientation normal to the reflected beam. Figure 3 3

4 Figure 4 shows the viewing of a diffractive element image on an Optical Security Media card using a laser and a screen. Figure 4 The Diffractive Viewer Figure 5 shows the LaserCard Optical Security Viewer, a device which displays the holographic Diffractive Image created by each diffractive element on the card. The card is swiped through a slot and the image is seen on the screen. This is easy to do and allows the operator to quickly verify that the Diffractive Image is present on the card and, therefore, that the Optical Security Media is authentic. Figure 5 LaserCard Optical Security Viewer Within the Viewer, the laser module is a low cost assembly consisting of a laser, a collimating lens, and a circuit board with a pot to adjust the power. The circuitry has a regulator which maintains constant optical power 4

5 even as the battery voltage decreases with loss of charge. This laser module is designed to use an inexpensive laser source with a visible collimated beam, such as that in a laser pointer. A Lithium rechargeable battery provides the power to the laser module. A circuit board connects the battery to the laser via a switch which is activated when a card is swiped through the slot. The card pushes against a plastic ball, which in turn throws the switch arm. The circuit board provides a battery charger which draws power from a USB connector whenever it is connected to a USB host device such as a computer. The USB signal lines are not connected so the host device does not see the Optical Security Viewer but does provide 5 Volt power. The circuit board has a micro controller which monitors the battery voltage when the card switch is activated. If the voltage falls below a set level the processor flashes an LED on the board to warn the user that the battery needs to be recharged. The battery itself has an internal circuit which disconnects the battery from the outside world when its output voltage drops below a safe operating level. This prevents a deep discharge from damaging the battery. The Viewer also has a screen that displays the holographic image. The screen has a small hole located above the image area that allows light from the low battery voltage LED to pass through. Creating the Diffractive The Diffractive Image master is created using a specialized software program which takes many hours to create the master running on a high performance desktop computer. The creation of a new Diffractive Image starts with the creation of a bitmap (.BMP) file of 1024 by 1024 pixels with the desired holographic pattern in the lower right hand corner occupying pixels squared. The next step is to increase the size of the file to 2048 by 2048 pixels and input the file into the program which uses a trial and error method to generate the Diffractive Image master. A trial pattern is generated from the current best pattern estimate and the resulting diffraction pattern is computed and compared to previous computation. If the computed diffraction pattern is closer to the target pattern then the trial pattern becomes the best estimate and is used as the basis for the next iteration. The computed diffraction pattern is converted to a 2048 by 2048 bitmap image which can be viewed while the program is running. After about 24 hours of iteration the computation starts to resemble the actual resulting hologram as shown in Figure 6. Figure 6 Example of original bitmap image. 5

6 The resulting hologram pattern is the figure itself and a mirror image with the mirror plane passing diagonally through the bottom right hand corner as shown below. The distance from the figure to the corner thus determines the separation of the two hologram images. Figure 7 Resulting hologram image. The main output of the software program is a 2048 by 2048 bitmap image which is converted to a PCX file and incorporated into the card Photomask. Figure 8 shows a portion of the generated hologram pattern. Figure 8 Figure 9 shows the actual pattern on the Optical Security Media. Figure 9 6

7 Summary The Covert Diffractive Image embedded into LaserCard Optical Security Media based identity credentials is one of the most secure authentication features available. It cannot be reverse engineered or copied onto another card. Each graphic design is unique to the credential issuer and thus it provides complete assurance of media authenticity. The LaserCard Optical Security Viewer provides a very convenient, cost effective and easy to use means of verifying the presence of Covert Diffractive Image in any inspection setting whether at the border, in the field or elsewhere. Contact Us: To learn more about how LaserCard can support your secure ID solution with an optimized suite of overt, covert and forensic security features, please contact us at: The Americas: tel: , sales@lasercard.com Europe, Middle East & Africa: tel: ; sales.emea@lasercard.com 7