Abstract:
A helical physical unclonable function is disclosed. The helical physical unclonable function may be used to authenticate a supply item for an imaging device. Measurements of the magnetic field above a helical flight are stored in a non-volatile memory to be used by an imaging device to authenticate the supply item. Other systems and methods are disclosed.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The following applications are related and were filed contemporaneously: “MAGNETIC HELICAL PHYSICAL UNCLONABLE FUNCTION MEASURED ABOVE FLIGHT”, “MAGNETIC HELICAL PHYSICAL UNCLONABLE FUNCTION MEASURED ADJACENT TO FLIGHT”, “MANUFACTURING A HELICAL PHYSICAL UNCLONABLE FUNCTION”. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to anti-counterfeit systems and more particularly to physical unclonable functions. 
     2. Description of the Related Art 
     Counterfeit printer supplies, such as toner bottles, are a problem for consumers. Counterfeit supplies may perform poorly and may damage printers. Printer manufacturers use authentication systems to deter counterfeiters. Physical unclonable functions (PUF) are a type of authentication system that implements a physical one-way function. Ideally, a PUF cannot be identically replicated and thus is difficult to counterfeit. Thus, it is advantageous to maximize the difficulty of replicating a PUF to deter counterfeiters. It is also advantageous for the PUF and PUF reader to be low cost. 
     SUMMARY 
     The invention, in one form thereof, is directed to a supply item for an image forming device having a body; a physical unclonable function located on the body configured to rotate about an axis of rotation having a shaft centered on the axis of rotation and a helical flight having a length wrapped around the shaft, the helical flight has a top surface furthest away from the axis of rotation, the helical flight contains magnetized particles that generate a magnetic field above the top surface having a varying intensity along the length of the helical flight, the helical flight has a side surface between the shaft and the top surface; and a non-volatile memory located on the body containing a first array of numbers corresponding to the intensity of the magnetic field radial to the axis of rotation above the top surface along a section of the length of the helical flight at a first plurality of locations each at a first fixed distance from the side surface and also containing a digital signature generated from the first array of numbers. 
     The invention, in another form thereof, is directed to a supply item for an image forming device having a body; a physical unclonable function located on the body configured to rotate about an axis of rotation having a shaft centered on the axis of rotation, the shaft has a helical channel having a length wrapped around the shaft, the shaft contains magnetized particles that generate a magnetic field above the shaft having a varying intensity, the helical channel has a side surface; and a non-volatile memory located on the body containing a first array of numbers corresponding to the intensity of the magnetic field radial to the axis of rotation above the shaft along a section of the length of the helical channel at a first plurality of locations each at a first fixed distance from the side surface and also containing a digital signature generated from the first array of numbers. 
     The invention, in yet another form thereof, is directed to a supply item for an image forming device having a body; an auger having a spiral flight having magnetized particles that generate a magnetic field above the spiral flight having a varying intensity, the auger is rotatably mounted to the body; and a non-volatile memory located on the body containing an array of numbers corresponding to the intensity of the magnetic field above a section of the spiral flight and also containing a digital signature generated from the array of numbers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present disclosure, and together with the description serve to explain the principles of the present disclosure. 
         FIG. 1  is a block diagram of an imaging system including an image forming device according to one example embodiment. 
         FIG. 2  is a top view of a helical PUF. 
         FIG. 3  is a side view of a PUF reader. 
         FIG. 4  is a top view of a supply item for an imaging device having a helical PUF. 
         FIG. 5  is a graph of magnetic field intensity above a helical flight. 
         FIG. 6  is example values for generating a digital signature. 
         FIG. 7  is a top view of a helical PUF. 
         FIG. 8  is a section view of a helical PUF. 
         FIG. 9  is a section view of a helical PUF. 
         FIG. 10 ,  FIG. 11 , and  FIG. 12  are top views of a helical PUF. 
         FIG. 13  is a top view of a helical PUF. 
         FIG. 14  is a top view of a helical PUF. 
         FIG. 15  is a top view of a supply item for an imaging device having a helical PUF. 
         FIG. 16  is a flowchart of a method of manufacturing a supply item for an imaging device. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings where like numerals represent like elements. The embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the present disclosure. Examples merely typify possible variations. Portions and features of some embodiments may be included in or substituted for those of others. The following description, therefore, is not to be taken in a limiting sense and the scope of the present disclosure is defined only by the appended claims and their equivalents. 
     Referring to the drawings and particularly to  FIG. 1 , there is shown a block diagram depiction of an imaging system  50  according to one example embodiment. Imaging system  50  includes an image forming device  100  and a computer  60 . Image forming device  100  communicates with computer  60  via a communications link  70 . As used herein, the term “communications link” generally refers to any structure that facilitates electronic communication between multiple components and may operate using wired or wireless technology and may include communications over the Internet. 
     In the example embodiment shown in  FIG. 1 , image forming device  100  is a multifunction device (sometimes referred to as an all-in-one (AIO) device) that includes a controller  102 , a user interface  104 , a print engine  110 , a laser scan unit (LSU)  112 , one or more toner bottles or cartridges  200 , one or more imaging units  300 , a fuser  120 , a media feed system  130  and media input tray  140 , and a scanner system  150 . Image forming device  100  may communicate with computer  60  via a standard communication protocol, such as, for example, universal serial bus (USB), Ethernet or IEEE 802.xx. Image forming device  100  may be, for example, an electrophotographic printer/copier including an integrated scanner system  150  or a standalone electrophotographic printer. 
     Controller  102  includes a processor unit and associated memory  103  and may be formed as one or more Application Specific Integrated Circuits (ASICs). Memory  103  may be any volatile or non-volatile memory or combination thereof such as, for example, random access memory (RAM), read only memory (ROM), flash memory and/or non-volatile RAM (NVRAM). Alternatively, memory  103  may be in the form of a separate electronic memory (e.g., RAM. ROM, and/or NVRAM), a hard drive, a CD or DVD drive, or any memory device convenient for use with controller  102 . Controller  102  may be, for example, a combined printer and scanner controller. 
     In the example embodiment illustrated, controller  102  communicates with print engine  110  via a communications link  160 . Controller  102  communicates with imaging unit(s)  300  and processing circuitry  301  on each imaging unit  300  via communications link(s)  161 . Controller  102  communicates with toner cartridge(s)  200  and non-volatile memory  201  on each toner cartridge  200  via communications link(s)  162 . Controller  102  communicates with fuser  120  and processing circuitry  121  thereon via a communications link  163 . Controller  102  communicates with media feed system  130  via a communications link  164 . Controller  102  communicates with scanner system  150  via a communications link  165 . User interface  104  is communicatively coupled to controller  102  via a communications link  166 . Processing circuitry  121  and  301  may include a processor and associated memory such as RAM, ROM, and/or non-volatile memory and may provide authentication functions, safety and operational interlocks, operating parameters and usage information related to fuser  120 , toner cartridge(s)  200  and imaging unit(s)  300 , respectively. Controller  102  processes print and scan data and operates print engine  110  during printing and scanner system  150  during scanning. 
     Computer  60 , which is optional, may be, for example, a personal computer, including memory  62 , such as RAM, ROM, and/or NVRAM, an input device  64 , such as a keyboard and/or a mouse, and a display monitor  66 . Computer  60  also includes a processor, input/output (I/O) interfaces, and may include at least one mass data storage device, such as a hard drive, a CD-ROM and/or a DVD unit (not shown). Computer  60  may also be a device capable of communicating with image forming device  100  other than a personal computer such as, for example, a tablet computer, a smartphone, or other electronic device. 
     In the example embodiment illustrated, computer  60  includes in its memory a software program including program instructions that function as an imaging driver  68 , e.g., printer/scanner driver software, for image forming device  100 . Imaging driver  68  is in communication with controller  102  of image forming device  100  via communications link  70 . Imaging driver  68  facilitates communication between image forming device  100  and computer  60 . One aspect of imaging driver  68  may be, for example, to provide formatted print data to image forming device  100 , and more particularly to print engine  110 , to print an image. Another aspect of imaging driver  68  may be, for example, to facilitate the collection of scanned data from scanner system  150 . 
     In some circumstances, it may be desirable to operate image forming device  100  in a standalone mode. In the standalone mode, image forming device  100  is capable of functioning without computer  60 . Accordingly, all or a portion of imaging driver  68 , or a similar driver, may be located in controller  102  of image forming device  100  so as to accommodate printing and/or scanning functionality when operating in the standalone mode. 
     Several components of the image forming device  100  are user replaceable e.g. toner cartridge  200 , fuser  120 , and imaging unit  300 . It is advantageous to prevent counterfeiting these user replaceable components. A PUF  202  may be attached to the toner cartridge  200  to prevent counterfeiting as described below. A PUF reader  203  may be integrated into the image forming device  100  to verify the authenticity of the PUF  202 . Data related to the PUF  202  may reside in non-volatile memory  201 . 
       FIG. 2  shows PUF  202  with a helical flight  210  wrapped around a shaft  212 . The helical flight  210  and the shaft  212  may be one integrated part. Alternatively, they may be two separate parts attached together. The PUF  202  has a pair of cylindrical supports  214 ,  216  that extend laterally from each end of the PUF  202 . In operation, the PUF  202  rotates about an axis of rotation  218 . The cylindrical supports  214 ,  216 , the shaft  212 , and the helical flight  210  are centered on the axis of rotation. The helical flight  210  may be referred to as an auger, and the helical flight  210  may be referred to as a spiral flight. 
     The helical flight  210  contains magnetized particles that generate a magnetic field above the top surface  220  of the helical flight  210 . The magnetized particles are, for example, flakes of an alloy of neodymium, iron and boron (NdFeB). The shaft  212  may contain magnetized particles to add complexity to the magnetic field. The PUF  202  may be located on a body of a supply item for an image forming device such as, for example, toner cartridge  200 . When the toner cartridge  200  is located in the image forming device  100 , the PUF  202  interfaces with the PUF reader  203 , which contains a magnetic field sensor  222  mounted to a printed circuit board (PCB)  224 . The PCB  224  also has a locating pin  226 . 
       FIG. 3  shows a side view of the PUF reader  203 , including the magnetic field sensor  222 , the PCB  224 , and the locating pin  226 . The locating pin  226  is taller than the magnetic field sensor  222 . When the PUF reader  203  is engaged with the PUF  202 , preferably the locating pin  226  rides on the shaft  212  and the magnetic field sensor  222  is located above the helical flight  210  without contacting the helical flight  210 . The locating pin material and shape may be selected to minimize the drag against the PUF  202 . Alternatively, the magnetic field sensor  222  may ride on the helical flight  210 . The PUF reader  203  is mounted such that it is free to move in a compliance direction  310  that is preferably radial to the axis of rotation  218 . Preferably, the PUF reader  203  is biased by a spring against the shaft  212 . This mounting compliance helps accommodate mechanical and positional tolerances between the PUF  202  and the PUF reader  203 , which improves reliability and reduces manufacturing costs. The magnetic field sensor  222  may make measurements radial to the axis of rotation  218  i.e. parallel to the compliance direction  310 . The magnetic field sensor  222  may make measurements parallel to the axis of rotation  218  i.e. perpendicular to the compliance direction  310 . The magnetic field sensor  222  may make measurements in three orthogonal directions. 
     The locating pin  226  is biased against a side surface  230  of the helical flight  210 . The magnetic field sensor  222  follows a measurement path  228  along a section of the helical flight  210 . The measurement path  228  is at a fixed distance from the side surface  230 . The distance between the magnetic field sensor  222  and the locating pin  226  as well as the angle between the PUF reader  203  and the helical flight  210  determines the fixed distance. 
     In operating, the PUF reader  203  is moved parallel to the axis of rotation  218 . The locating pin  226  pushes against the side surface  230 , causing the PUF  202  to rotate about the axis of rotation  218 . Sine the locating pin  226  remains in contact with the side surface  230 , the positional accuracy of the measurement path  228  will be excellent. This is important, since shifting the measurement path  228  laterally by a small amount may radically change the magnetic field seen by the magnetic field sensor  222 . The helical PUF  202  is superior to a linear PUF since translation of the PUF reader to read the PUF also maintains the position of the PUF reader relative to the PUF. Preferably, the magnetic field sensor  222  and locating pin  226  are aligned parallel to the axis of rotation  218  to prevent a counterfeiter from replacing the helical PUF  202  with a linear PUF since the locating pin  226  would raise the magnetic field sensor  222  too far above the linear PUF. 
     The helical flight  210  has a helix angle  232 . Preferably, the helix angle  232  is between thirty degrees and sixty degrees inclusive. If the helix angle  232  is less than thirty degrees the PUF  202  may bind and fail to rotate. If the helix angle  232  is more than sixty degrees the PUF  202  may fail to maintain contact between the locating pin  226  and the side surface  230 . Preferably, the helix angle  232  is less than sixty degrees so the maximum helical flight length may be provided for a given PUF length, since a longer PUF is harder to duplicate than is a shorter PUF. 
       FIG. 4  shows the helical PUF  202  located on a supply item for an imaging device e.g. toner cartridge  200 . The toner cartridge  200  has a body  410  for holding toner. The helical PUF  202  is rotatably mounted to the body by bearings  412 ,  414  that encircle the cylindrical supports  214 ,  216 . Non-volatile memory  201  is also located on the body  410  and is mounted to a PCB  416  having a column of electrical contact pads  418 . The non-volatile memory  201  may contain an array of numbers corresponding to the intensity of the magnetic field along a section of the measurement path  228 . The non-volatile memory  201  may also contain a digital signature generated from the array of numbers. To clone the toner cartridge, a counterfeiter must either duplicate a genuine helical PUF and also duplicate the accompanying non-volatile memory, which is difficult, or the counterfeiter must create a counterfeit helical PUF and also create a properly signed array of measurements corresponding to the counterfeit PUF, which is also difficult. Thus, the toner cartridge  200  is protected from counterfeiting. 
       FIG. 5  shows a graph  500  of the intensity  510  of an example magnetic field along a section of the measurement path  228 . An array of numbers  512  corresponds to the magnetic field intensity measured at regular intervals along the path, as shown by dotted lines  514  on the graph. Preferably, the array of numbers  512  are integers to simplify processing. Alternatively, the array of numbers may be, for example, floating point. The numbers in  FIG. 5  and  FIG. 6  are in hexadecimal format. 
       FIG. 6  shows an example of generating a digital signature from the array of numbers  512 . Other algorithms for generating a digital signature are known in the art. The digital signature is used by the controller  102  to verify that the PUF data in the non-volatile memory is authentic. The toner cartridge&#39;s serial number  610  and the array of numbers  512  are combined to form a message  612 . Preferably, the message is encrypted. Alternatively, the message may be unencrypted. For this example, AES-CBC is used (see, for example, RFC3602 “The AES-CBC Cipher Algorithm and Its Use with IPsec” published by The Internet Society (2003), and NIST (National Institute of Standards) documents FIPS-197 (for AES) and to SP800-38A (for CBC)). The AES key  614  and CBC Initialization Vector (IV)  616  are used as is known in the an to generate the encrypted message  618 . In this example, to sign the encrypted message  618  first the message is hashed then the hash is encrypted with the private key  620  of an asymmetric key pair that includes a public key  622 . This example uses the SHA-512 hashing algorithm and Elliptic Curve Digital Signature Algorithm (ECDSA) utilizing a P-512 curve key, as is known in the art. Other algorithms are known in the art. The SHA-512 hash  624  of the encrypted message  618  is used to generate an ECDSA P-512 digital signature  626 . The signature  626  and encrypted message  618  are stored in the non-volatile memory  201 . The image forming device  100  may use the array of numbers  512  in the encrypted message  618  to verify the authenticity of the helical PUF  202 , and the image forming device  100  may use the digital signature  626  to verify the authenticity of the array of numbers  512 . In this way, the image forming device  100  may verify the authenticity of the toner cartridge  200 . 
       FIG. 7  shows the helical PUF  202 .  FIG. 8  shows a section view of the helical PUF  202  cut along cross-section line  710 . In this example, the shaft  212  and the helical flight  210  are two separate parts attached together. The helical flight  210  contains magnetized particles  810 ,  812  that generate a magnetic field above the top surface  220  and adjacent to the side surface  230 . The helical flight  210  has a rectangular cross section. The side surface  230  is planar which improves the locating tolerance of the locating pin  226 .  FIG. 9  shows an alternate embodiment with the helical flight  210  having a semi-circular cross section. The side surface  230  is curved which reduces the friction between the locating pin  226  and the helical flight  210 . Other helical flight cross sections may be used e.g. triangular, etc. 
       FIG. 10  shows an alternate embodiment of a helical PUF  1002 . The helical flight is a shaft  1010  that has a helical channel  1050  wrapped around the shaft  1010 . The shaft  1010  contains magnetized particles that generate a magnetic field above the shaft  1010  having varying intensity. The helical channel  1050  has a first side surface  1030 . The helical PUF  1002  is configured to rotate about an axis of rotation  1018 . A pair of cylindrical supports  1014 ,  1016 , the shaft  1010 , and the helical channel  1015  are centered on the axis of rotation. 
     In operation, the locating pin  226  of the PUF reader  203  pushes against the first side surface  1030 , causing the magnetic field sensor  222  to follow a first measurement path  1028  along a section of the length of the helical channel  1050 . The first measurement path  1028  is at a first fixed distance  1052  from the side surface  1030 . In this example, the PUF reader  203  is moving from right to left.  FIG. 11  shows the helical PUF  1002  while the PUF reader  203  is moving from left to right. The locating pin  226  pushes against a second side surface  1054  of the helical channel  1050 , causing the magnetic field sensor  222  to follow a second measurement path  1129  located a second fixed distance  1156  from the first side surface  1030 . The second fixed distance  1156  is shorter than the first fixed distance  1052 . Thus, a single helical PUF  1002  with a single PUF reader  203  may measure two different measurement paths by alternating the direction of travel of the PUF reader  203 . This makes it more difficult to counterfeit the helical PUF  1002 , since two measurement paths must be duplicated. In operation, preferably the PUF reader  203  initially moves by at least the helical channel pitch  1157  to be sure the locating pin  226  falls into the helical channel. Then, the PUF reader  203  moves in the opposite direction at least a distance equal to the helical channel pitch since the actuator moving the PUF reader  203  will be designed to travel at least that distance. 
       FIG. 12  shows an alternate PUF reader  1203  that may measure along two measurement paths  1028 ,  1228  simultaneously. The PUF reader  1203  has two magnetic field sensors  1222 ,  1223  located on opposite sides of a locating pin  1226 . 
       FIG. 13  shows an alternate embodiment of a helical PUF  1302 . A helical channel  1350  wraps around a shaft having magnetized particles. The helical channel  1350  terminates in a stop  1366  at the left end and a second stop  1368  at the right end  1368 . In operation, the PUF reader  203  may be moved laterally along the helical PUF  1302  from left to right until the locating pin  226  hits stop  1368 . The controller  102  may detect this event by monitoring drive current to a motor that moves the PUF reader  203 . When this event is detected, the controller  102  knows the PUF reader  203  is at a home position relative to the PUF  1302 . Knowing this helps the controller  102  to align data measured along a measurement path with data stored in the toner cartridge non-volatile memory. A second home position may be at stop  1366 . 
       FIG. 14  shows an alternate PUF reader  1472  that measures a magnetic field adjacent to the side surface  1030 . The PUF reader  1472  has a magnetic field sensor  1470  that measures the intensity of the magnetic field normal to the side surface  1030  and parallel to the side surface. The PUF reader  1472  touches the side surface  1030  with a pair of spacers  1474 ,  1476 . In operation, the PUF reader  1472  is moved parallel to the axis of rotation to measure a section of the length of the helical channel  1050 . 
       FIG. 15  shows an alternate embodiment of a supply item for an imaging device e.g. toner cartridge  1500 . The toner cartridge  1500  has a body  1505  for holding toner. A helical PUF  1502  is configured to slide laterally along a drive shaft  1580  located on an axis of rotation  1518  of the helical PUF  1502 . The drive shaft  1580  may be turned by a drive gear  1584  that is coupled to a motor located in the imaging device  100 . The helical PUF  1502  is rotatably mounted to the body  1505  by bearings  1512 ,  1515 . The drive shaft  1580  has a flat area  1582  which gives the drive shaft  1580  a “D” shaped cross section i.e. the drive shaft  1580  is a D-shaft. The helical PUF  1502  has a “D” shaped hole around the axis of rotation  1518  that is larger than the cross section of the drive shaft  1580 . Thus, the helical PUF  1502  will rotate when the drive shaft  1580  is rotated and the helical PUF  1502  is free to slide laterally along the drive shaft  1580  parallel to the axis of rotation. 
     The helical PUF  1502  has a helical flight  1510  and a helical channel  1550 . The helical flight  1510  contains magnetized particles that generate a magnetic field adjacent to the helical flight  1510 . A PUF reader  1503 , located in the imaging device  100 , has a locating pin  1526  and a magnetic field sensor  1522 . The PUF reader  1503  is fixedly mounted to the imaging device  100 . In operation, rotation of the drive shaft  1580  causes a side surface of the helical flight  1510  to contact the locating pin  1526 , which causes the helical PUF  1502  to slide laterally along the drive shaft  1580 . The magnetic field sensor  1522  reads the intensity of the magnetic field along a section of the length of the helical flight, and the controller  102  compares the measured field to an array of numbers stored in a non-volatile memory  1501  mounted to the body  1505 . Alternatively, the magnetic field sensor may be located in the helical channel  1550  and measure along a side surface. This embodiment simplifies mounting the PUF reader  1503  since the PUF reader  1503  does not require a mechanism to translate laterally along the helical PUF  1502 . 
     Preferably, the locating pin  1526  is positioned offset from the axis of rotation  1518  to provide a torque on the helical PUF  1502  relative to the drive shaft  1580 . This torque increases the friction between the helical PUF  1502  and the drive shaft  1580  to insure continuous contact between the locating pin  1526  and the helical flight  1510 . 
       FIG. 16  shows an example embodiment of a method of manufacturing a supply item for an imaging device according to one embodiment. Method  1600  creates a supply item that is difficult to counterfeit. 
     At block  1610 , a body is obtained. The body may be, for example, suitable to hold toner for an imaging device. At block  1612 , a helical auger is obtained. The helical auger has a spiral flight having magnetized particles generating a magnetic field above the flight having a varying intensity. At block  1614 , a non-volatile memory device is obtained. At block  1616 , the non-volatile memory device is attached to the body. At block  1618 , the helical auger is rotatably attached to the body. 
     At block  1620 , an array of measurements are created by measuring the intensity of the magnetic field along a section of the spiral flight. At block  1622 , a digital signature is generated from the array of measurements. At block  1624 , the array of measurements is stored in the non-volatile memory device, and the digital signature is stored in the non-volatile memory device. These blocks may be performed in alternate orders. 
     The foregoing description illustrates various aspects and examples of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.