Abstract:
A system and method for creating a unique optical signature that uses a plurality of optical signature chambers containing fluids having differing optical properties, for example differing indices of refraction, that produce different individual optical signatures for each chamber. If the chambers are broken causing the fluids to spill or the fluids are otherwise discharged from the chambers, the fluids mix together so one does not know which fluid came from which chamber, thereby preventing replication of the correct optical signatures. This destruction of the optical signatures can occur mechanically, without the application or presence of electrical power.

Description:
FIELD 
     This disclosure relates to a system and method for creating a unique optical signature. 
     BACKGROUND 
     There are many different applications for unique signatures or identifiers. For example, a unique signature can be used to uniquely identify a specific physical object within a group. One example of the use of a unique signature is a unique number that is calculated and assigned to a piece of electronic equipment. If that unique number is not recalculated correctly upon attempted operation of the electronic equipment, thereby indicating possible tampering with the equipment, then the electronic equipment is not allowed to operate. Another area of use of a unique signature is in encryption technology in which a unique encryption key is generated and stored in non-volatile random access memory. 
     In certain applications, particularly high security applications, it is important to prevent unauthorized access to the unique signature in order to prevent duplication or replication of the signature that can, for example, be used to gain unauthorized access to sensitive data or allow unauthorized use of equipment. In the case of current encryption technology, the encryption key is intended to be erased from memory if an unauthorized person tries to access the encryption key. However, this active erasure approach requires active power or a battery source, which is not necessarily always present. Additionally, the erasure timeline of an active erasure approach may be too long for some application environments. 
     SUMMARY 
     A system and method are described for creating a unique optical signature that uses a plurality of optical signature chambers containing fluids having differing optical properties that produce different individual optical signatures for each chamber. If the chambers are broken causing the fluids to spill or the fluids are otherwise discharged from the chambers, the fluids mix together so one does not know which fluid came from which chamber thereby preventing replication of the correct individual optical signatures and preventing replication of the correct arrangement of the individual optical signature. This destruction of the optical signatures can occur mechanically, without the application or presence of electrical power. 
     The resulting unique optical signature of the system is created by directing light through the fluid of each optical signature chamber and detecting the resulting optical signature that is produced by the fluid in each chamber. The individual optical signature of each signature chamber can be unique to that signature chamber, or some of the signature chambers can share the same individual optical signature. The individual optical signatures of each chamber together form an overall resulting unique optical signature of the system. 
     The resulting unique optical signature can be used in any of a large number of applications including, but not limited to, the construction of an encryption key or uniquely identifying an object such as an electronic device. Any application that would benefit from using a unique signature could utilize the system and method described herein. 
     In one embodiment, an optical signature system includes at least one light source, and at least two optical signature chambers each defining an interior space containing fluid. The fluids have differing optical properties whereby the optical signature chambers have differing individual optical signatures. An optical signature detector detects light from one or more of the at least two optical signature chambers as a result of light being directed through the optical signature chambers. In one embodiment, a plurality of optical signature detectors are provided that electrically detect the differing individual and resulting optical signatures of the optical chambers as a result of light being directed therethrough. 
     The detected optical signatures can then be processed, for example by comparing the resulting detected light patterns with stored patterns to determine if there is a match, or by comparing values representative of the intensities of the detected light signatures with stored intensity values. 
     An encryption key can be created using the optical signature chambers. If the detected optical signatures are determined to be valid, a correct key is generated that can be used to encrypt/decrypt data. 
    
    
     
       DRAWINGS 
         FIG. 1  depicts an optical signature system. 
         FIG. 2  is a top perspective view of a plurality of optical signature chambers arranged into an array. 
         FIG. 3  is a detailed view of an optical signature chamber used in  FIGS. 1 and 2 . 
         FIG. 4  illustrates the fluids in the signature chambers spilled from the optical signature chambers and mixed together. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , an optical signature system  10  is illustrated. The system  10  includes at least one light source  12 , at least one optical signature chamber  14 , and at least one optical signature detector  16 . The light source  12  is intended to direct light into and through the chamber  14  which is designed to create a unique optical signature as a result of refraction and/or reflection of the light as the light passes through the chamber. The optical signature can be the resulting pattern of light or portion of the pattern emerging from the chamber  14 , the intensity of one or more pixels of light emerging from the chamber  14 , or any other measure of the light emerging from the chamber  14 . The detector  16  is designed to detect the resulting unique optical signature produced by the chamber  14  as the light emerges from the chamber. The detector  16  may resolve a single point or an array of points and will accept light from at least one optical signature chamber. The detector  16  can be, for example, a pin diode that produces a single intensity output, or a charge-coupled device (CCD) which receives a relatively wider area of light and produces an array of values as an output, i.e. an image, each relating intensity or color. 
     As used herein, the optical signature produced by each optical signature chamber  14  will be referred to as an individual optical signature. The individual optical signatures of the chambers  14  together form a resulting unique optical signature for the system  10 . In some circumstances, the light waves emerging from the individual optical signature chambers  14  may continue to interact and interfere with each other as they exit the optical chambers, and it is the result of the interfering and interacting light waves that is detected and forms the resulting optical signature of the system. 
     The number of chambers  14  and the arrangement of the chambers in a pattern or array can vary based on a number of factors, including the particular security application and how many different individual optical signatures need to be created. The chambers  14  are arranged adjacent to one another so as to receive the light from the light source  12 . As shown in  FIG. 2 , the chambers  14  can be arranged into a pattern, for example an array of rows and columns, for example four rows and five columns. At least two chambers  14  having differing individual optical signatures is required. The larger the number of chambers  14 , the more individual optical signatures that are created and in general the more unique the resulting optical signature of the system  10 . However, for the same number of chambers  14 , changing the pattern of the chambers and the locations of the various chambers in the pattern alters the resulting unique optical signature for the entire system  10 . 
     Covers  18 ,  20  can be provided over the ends of the chambers  14  to close off the ends of the chambers  14 . The covers  18 ,  20  are designed to allow passage of light waves into and from the chambers  14 . The covers  18 ,  20  can be, for example, made of a material that permits passage of the light, such as clear glass. Alternatively, the covers  18 ,  20  can be light transmissive only in the locations where they directly cover the chambers. 
     A single or multiple light sources  12  can be used for directing light into the chamber(s)  14 . In the illustrated embodiment, the light source(s)  12  and the chambers  14  are arranged so that the light enters through a longitudinal end of the chambers, and exits through an opposite longitudinal end. If multiple light sources are used, there can be one light source for each chamber  14  or multiple chambers can share a common light source. The light provided by the light source  12  is preferably visible light, more preferably monochromatic light, for example coherent light from a laser. However, in certain applications, other types of visible light, such as white light, could be used. In addition, non-visible light, for example infra-red light, could be used. Any light source that provides a light wave that can be detected by a suitable optical detector  16  after passing through the signature chamber(s)  14  can be used. 
     The number and type of detectors  16  used corresponds to, for example, the uniqueness required for the application. The detectors  16  can be any optical detector that can detect the light that emerges from at least one chamber  14 . For example, the detectors  16  can be an array of photodetectors. In the illustrated embodiment, there is at least one detector  16  for each chamber  14 . It is to be realized that each sensor can receive light that emerges from its associated chamber, as well as light that emerges from one or more adjacent chambers. Each detector  16  can be of a type that produces a single bit of information, such as a pin diode. Alternatively, the detectors  16  can be, for example, CCD imaging sensors which can generate an array of values corresponding to a variation in intensity and color, i.e. a light image. 
     The chambers  14  can be any container defining an interior space, and, in the illustrated embodiment, are open at each end. In one embodiment, each chamber  14  comprises a glass cylinder with open ends. The chambers can be designed to break under certain conditions, such as application of sufficient mechanical force. 
     With reference to  FIG. 3 , each chamber  14  contains a fluid  22  having optical properties suitable for producing an individual optical signature. These optical properties can include, for example, indices of refraction, opacity, and wavelength filtering or combinations thereof. In one embodiment, the optical properties of the fluid in each of the chambers  14  will be different whereby each chamber  14  produces a different individual optical signature. In other embodiments, some of the chambers can contain the same fluid or dissimilar fluids having the same optical properties so that they produce the same individual optical signatures. Nonetheless, not all chambers  14  will produce the same individual optical signature and the chambers  14  will be arranged such that the resulting optical signature for the entire system  10  is unique. 
     Any of a large number of different kinds of fluids can be used. The fluids can be, for example, optical coupling gels available from Dow Corning Corporation of Midland, Mich. The viscosity of the fluids in the chambers can vary from very viscous fluids such as liquids including water, to less viscous fluids such as gels. In addition, the fluids can be gases having differing optical properties. 
     The fluid in each chamber  14  can be homogenous or a mix of two or more fluids. Colorant can be added to the fluid to alter the color of the fluid. 
     The chambers  14  can be completely filled with fluid so that reorientation of the chambers does not alter the individual optical signatures. In another embodiment, the chambers are only partially filled with fluid. Thus, if the orientation of the chambers is altered sufficiently (for example by tilting the chambers from a vertical orientation shown in  FIG. 1  to a horizontal orientation), the fluids shift within the chambers and the individual optical signatures are altered since the light path through the chambers changes. 
     Further, the fluids used are preferably optically stable so as to maintain their optical characteristics over time. Nonetheless, one or more of the fluids can be designed to optically degrade or change in some manner when exposed to certain operating conditions. For example, the optical properties of one or more of the fluids can be designed to change when the chambers are exposed to certain environmental conditions, such as temperature extremes or when exposed to x-rays, or when exposed to certain operational conditions, such as vibration or shock extremes. 
     The system  10  is preferably designed such that attempted tampering with the chamber(s)  14  or application of sufficient force to the chamber(s) destroys the chamber(s) or causes the fluids to spill from the chambers, which thereby alters the individual optical signatures that are created by the chambers. For sake of convenience, any event that causes the fluids to spill from the chambers will be described herein as a destructive event. 
     Returning to  FIG. 1 , in one exemplary operational use of the system  10 , the individual optical signature of the chambers  14  are first established by the detectors  16  and the individual optical signatures saved in a suitable storage device such as random access memory of a data processing device. This establishes the signatures of each of the chambers  14 , and thus establishes the unique fingerprint of the device  10  and the machine, mechanism, device, etc. that the device  10  is used with. 
     During operational use, light from the light source  12  is directed through the chambers  14  and the resulting optical signatures of all chambers  14  are detected by the detectors  16 . For example, as discussed above, the detectors  16  can detect the light images produced by the chambers, which images are then compared to the expected light images which have previously been stored. If the light images match the stored images, a key bit sequence  24  can be created which is then compared to an expected key bit sequence to determine a match. If one or more of the detected light images does not match a stored image, the correct key bit sequence is not generated. Thus, an action or operation of equipment can be prevented, and/or a suitable notification can be sent warning of the error. In another embodiment, the generated key bit sequence can be inserted directly into a decryption algorithm. The failure to decrypt correctly would result in an inoperable equipment state. 
     The comparison of the detected optical signature to the expected optical signature can also be used as a simple go/no-go tool without creating a key bit sequence, whereby if there is a match an action can be permitted to take place or equipment allowed to operate. Conversely, if there is not a match, the action or operation of equipment can be prevented, and/or a notification can be sent warning of the error. 
     Instead of detecting a light image, the detectors can detect a light intensity of each chamber and compare the detected light intensity with a previously stored expected light intensity. 
     In addition, rather than comparing the detected optical signature(s) to a stored optical signature(s), the detected optical signature can be used as an input for another process. For example, the detected optical signatures can be represented in the digital world as a plurality of 1&#39;s and 0&#39;s as suggested by the key bit sequence  24 . The 1&#39;s and 0&#39;s representing the detected optical signature can be fed into a random number generator which processes the numbers to create a code that is used to encrypt data that is sent to another location which must have the correct code to decrypt the data. 
     If a destructive event occurs, the fluids are spilled from the chambers  14  as shown in  FIG. 4  and mix with each other. Once the fluids mix, the optical signatures of each chamber cannot be recreated because one cannot tell which fluid came from which chamber. Therefore, destruction of the optical signature of the system  10  can be achieved by spilling the fluids from the chambers  14 . Such destruction can be performed mechanically or manually, without the need for electric power. 
     The embodiments disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.