Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of application Ser. No. 13/288,381 filed on Nov. 3, 2011, entitled “TAMPER RESISTANCE EXTENSION VIA TAMPER SENSING MATERIAL HOUSING INTEGRATION”, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Physical device security is essential when a device holding secret data is to be placed in potentially unfriendly hands. To protect the secret data, the device can be configured to sense attempted physical access (e.g., tampering) to the device and can zeroize the data upon the attempted physical access. In order to easily zeroize the data, it can be stored on a memory device (e.g., a volatile random access memory (RAM)). Sensing the attempted physical access to the device can be accomplished with a tamper sensitive material disposed to detect attempted access to the memory device. When the tamper sensitive material senses an attempted access to the memory device, the memory device can be zeroized thereby rendering the secret data unobtainable. 
       SUMMARY 
       [0003]    Systems and apparatuses disclosed herein provide for a tamper resistant electronic device. The electronic device can include a circuit board, a shell, an anti-tamper material, a memory, one or more sensors, and tamper responsive electronics. The one or more sensors can be configured to sense when the shell moves away from the circuit board. The anti-tamper material can be about the first portion of the shell and disposed to protect the memory, one or more sensors, and the tamper responsive electronics. The tamper responsive electronics on the circuit board can be coupled to the anti-tamper material and the one or more sensors, and can be configured to zeroize data in the memory if tampering is sensed by the anti-tamper material or if one or more of the one or more sensors sense the shell has moved away from the circuit board. 
     
    
     
       DRAWINGS 
         [0004]    Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which: 
           [0005]      FIG. 1A  is a perspective view of an example of an electronic device including a plurality of electronic components protected from tampering by a tamper sensitive material. 
           [0006]      FIG. 1B  is a semi-exploded view of the electronic device of  FIG. 1A . 
           [0007]      FIG. 2  is a perspective view of an example printed circuit board and the tamper sensitive material from the electronic device of  FIG. 1A . 
           [0008]      FIG. 3  is a cross-sectional view of the electronic device of  FIG. 1A . 
           [0009]      FIG. 4  is a block diagram of example components for the electronic device of  FIG. 1A . 
       
    
    
       [0010]    In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments. 
       DETAILED DESCRIPTION 
       [0011]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the method presented in the drawing figures and the specification is not to be construed as limiting the order in which the individual steps may be performed. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0012]      FIGS. 1A and 1B  illustrate an example of an electronic device  100  including a plurality of electronic components protected from tampering by a tamper sensitive material. In an example, the tamper sensitive material can be integrated into a larger housing  104  for the electronic device  100 . The electronic device  100  can include a printed circuit board (PCB)  102  that is mounted to the housing  104  (e.g., a shell). The PCB  102  can include a plurality of electronic components mounted thereon and configured to implement the electronic functions of the electronic device  100 . The electronic device  100  can also include a tamper sensitive material  106  (e.g., a security shield, anti-tamper material) disposed to protect one or more of the electronic components on the PCB  102 . In an example, the tamper sensitive material  106  can be integrated into the housing  104 . 
         [0013]      FIG. 1A  is a view of the electronic device  100  showing the housing  104  in an open position. In an example, the housing  104  comprises multiple parts that are configured to be connected together and can substantially surround the PCB  102 . As shown in  FIG. 1A , a first part  104 - 1  of the housing  104  can be configured to cover a first side (e.g., a bottom) of the PCB  102  and a second part  104 - 2  of the housing  104  can be configured to cover a second side (e.g., a top) of the PCB  102 . The first part  104 - 1  can be configured to connect with the second part  104 - 2  to substantially surround the PCB  102 . To secure the PCB  102  in place, the PCB  102  can be mounted to the housing  104 , for example, by mounting the PCB  102  to the first part  104 - 1 . The housing  104  can be composed of any suitable material including plastic, metal, or other materials. 
         [0014]    In an example, the tamper sensitive material  106  can be integrated into the housing  104 , for example, into the second part  104 - 2  of the housing  104 . For example, the tamper sensitive material  106  can be integrated into the housing  104  by bonding one or more layers of the tamper sensitive material  106  to a surface of the housing  104 . The tamper sensitive material  106  can be disposed about the housing  104  such that when the housing  104  is secured around the PCB  102 , the tamper sensitive material  106  covers one or more of the electronic components on the PCB  102 . Accordingly, the tamper sensitive material  106  can be disposed to protect one or more electronic components by sensing attempted access of (e.g., tampering with) the one or more electronic components. The one or more electronic components on the PCB  102  that are protected by the tamper sensitive material  106  are referred to herein as the highly protected components  108 . In an example, the highly protected components  108  can include one or more processing devices coupled to one or more memory devices. The one or more memory devices can have data stored therein to which access can be restricted by the physical security of the electronic device  100 . The one or more memory devices can include any type of data including encryption keys, confidential information, software, or other data. 
         [0015]    If tampering is sensed by the tamper sensitive material  106 , the data within the one or more memory devices can be zeroized. In one example, the one or more memory devices holding the data can comprise volatile memory, and zeroizing the data can include removing power from the one or more memory devices, thereby removing the data from the memory. Accordingly, the highly protected components  108  can include security electronics that are coupled to the tamper sensitive material  106  and are configured to zeroize the data in the one or more memory devices based on a state of the tamper sensitive material  106 . In an example, the tamper sensitive material  106  is a passive sensor having a plurality of states, wherein each state provides a different reading for the sensor. Accordingly, the security electronics can obtain a reading to determine the state for the tamper sensitive material  106 . The tamper sensitive material  106  can be a capacitive sensor (e.g., a touch sensitive material), an impedance sensor (e.g., formed of Kapton®), an inductive sensor, or other sensing material. In some examples, multiple layers of the tamper sensitive material  106  can be used. In some examples, the tamper sensitive material  106  can include a flexible touch sensitive circuit. Accordingly, some examples of the tamper sensitive material  106  can detect simple touching of the tamper sensitive material  106 . These touch sensitive tamper materials can be used to provide aggressive security for the highly protected components  108 . 
         [0016]    In operation, the security electronics can obtain a first reading from the tamper sensitive material  106  prior to an attempted tampering. Then, the security electronics can operate in secure mode by continually obtaining readings from the tamper sensitive material  106 . If the reading from the tamper sensitive material  106  changes in a manner that indicates an attempted tampering, the security electronics can zeroize the data in the one or more memory devices coupled thereto. 
         [0017]      FIG. 1B  is a semi-exploded view of the electronic device  100  showing the housing in an open position and the tamper sensitive material  106  in an intermediate position to illustrate its position with respect to the circuit board  102 . As mentioned above, the tamper sensitive material  106  can be disposed to protect the highly protected components  108 . In an example, in order to protect the highly protected components  108  the tamper sensitive material  106  can be disposed to cover the highly protected components  108  and generally form an enclosure for the highly protected components  108  using the surface of the PCB  102 . That is, the highly protected components  108  can be mounted on a surface of the PCB  102 . The tamper sensitive material  108  can be disposed opposite the first surface of the PCB  102 , over the highly protected components  108 , and extend such that the tamper sensitive material  108  is adjacent to and detached from the first surface around a perimeter of the highly protected components  108 . Additionally, the PCB  102  can be constructed such that the attempted access to the highly protected components  108  through a second side (the reverse side from the first surface) of the PCB  102  can cause the data in the one or more memory devices to be zeroized and/or can render the highly protected components  108  inoperable. In an example, the PCB  102  has a layer of tamper sensitive material disposed therein which is coupled to the security electronics. Thus, attempted access through the tamper sensitive material in the PCB  102  can also cause the data in the one or more memory devices to be zeroized. In another example, the tamper sensitive material  108  can be disposed around both sides of the PCB  102  such that attempted access from both the first and second side of the PCB  102  can be detected by the tamper sensitive material  108 . 
         [0018]    Accordingly, physical access to the highly protected components  108  can be restricted from all directions. For example, attempted access through the second side of the PCB  102  can cause the data to be zeroized and/or can render the highly protected components  108  inoperable. Attempted access through the tamper sensitive material  108  can cause the security electronics to zeroize the data. Accordingly, the data in the one or more memory devices can be protected from unauthorized physical access. 
         [0019]    In an example, one or more sensors  110  can be mounted on the PCB  102  and can be configured to sense if the tamper sensitive material  106  is separated from the PCB  102 . In an example, the one or more sensors  110  can include a pressure sensor (e.g., a pressure sensitive switch, microswitch), wherein one or more features  112  physically associated with the tamper sensitive material  106  can be configured to contact and engage the pressure sensor when the tamper sensitive material  106  is closed over (e.g., protecting) the PCB  102 . If the tamper sensitive material  106  is separated from the PCB  102 , the pressure sensor will disengage. The disengaging of the pressure sensor can then be used to indicate that the tamper sensitive material  106  has separated from the PCB  102  and appropriate action can be taken. In another example, the one or more sensors  110  can include a light sensor (e.g., a photocell). When the tamper sensitive material  106  is closed the light sensor detects little light. If the tamper sensitive material  106  is separated from the PCB  102 , however, the light sensor can detect ambient light in the vicinity of the electronic device  100 . Thus, the light sensor can be used to indicate if the tamper sensitive material  106  is separated from the PCB  102 . In an example, both a light sensor and a pressure sensor can be used. 
         [0020]    In an example, the one or more sensors  110  can be included in the highly protected components  108 . Accordingly, the one or more sensors  110  can be highly protected from tampering. The one or more sensors  110  can be coupled to the security electronics to enable the security electronics to zeroize the data in the one or more memory devices if the one or more sensors  110  detect that the tamper sensitive material  106  has been separated from the PCB  102 . Thus, the one or more sensors  110  can provide additional protection for the highly protected components  108 . 
         [0021]    As shown in  FIG. 1A , the tamper sensitive material  106  can be integrated into the housing  104 . In particular, the tamper sensitive material  106  can be integrated into the second part  104 - 2  of the housing  104 . With the tamper sensitive material  106  integrated into the second part  104 - 2  of the housing  104 , the tamper sensitive material  106  will physically move with the second part  104 - 2  of the housing  104 . Accordingly, the one or more features  112  for engaging the pressure sensor of the one or more sensors  110  can be formed in the second part  104 - 2  of the housing  104 . Thus, the data in the one or more memory devices can be zeroized, if the second part  104 - 2  of the housing  104  is separated from the PCB  102 . In an example, the one or more features  112  can extend through the tamper sensitive material  106  in order to contact the one or more sensors  110 . To enable the one or more features  112  to extend through the tamper sensitive material  106 , the tamper sensitive material  106  can include one or more apertures corresponding to the one or more features  112 . The one or more features  112  can extend through the one or more apertures in the tamper sensitive material  106 . In an example, the apertures in the tamper sensitive material  106  can have a size (e.g., a diameter) that is similar to or smaller than a size of a contact area for the one or more sensors  110 . Keeping the size of the apertures of the tamper sensitive material  106  small can help to reduce the likelihood that the interior of the enclosure formed by the tamper sensitive material  106  can be accessed through the apertures. 
         [0022]    In addition to providing protection for the highly protected components  108 , the electronic device  100  can also provide tamper protection for electronic components outside the area protected by the tamper sensitive material  106 . This extended tamper protection can be provided by the security electronics detecting if the tamper sensitive material  106  has been separated from the PCB  102 . In particular, since the security electronics can detect when the second part  104 - 2  of the housing  104  and the integrated tamper sensitive material  106  are separated from the PCB  102 , the entire second part  104 - 2  can act as an extended tamper security shield. For example, the second part  104 - 2  can be formed to cover a larger area than the tamper sensitive material  106  such that the second part  104 - 2  extends to cover electronic components on the PCB  102  other than the highly protected components  108 . In an example, this larger area is at least twice as large as the area on the PCB  102  covered by the tamper sensitive material  106 . These other electronic components within the larger area and outside of the area covered by the tamper sensitive material  106  can be protected by having the security electronics take appropriate action if the second part  104 - 2  is separated from the PCB  102 . For example, the security electronics can zeroize the data in the one or more memory devices and/or can zeroize other data within the other components. In an example, the second part  104 - 2  of the housing  104  can extend to cover the entire first surface of the PCB  102 . In this way, tamper protection can be extended to the other components even through these other components are not covered by the tamper sensitive material  106 . Moreover, upon merely opening the housing  104  (e.g., separating the second part  104 - 2  from the PCB  102 ), the data in the one or more memory devices can be zeroized, thus providing increased protection for the highly protected components  108 . 
         [0023]    In some examples, one or more of the highly protected components  108  can produce a significant amount of heat. Dissipating the heat from these components can be challenging due to the tamper sensitive material enclosing the components. Accordingly, in some examples, the tamper sensitive material  106  can be configured such that heat can be dissipated from one or more of the highly protected components  108 . For example, the tamper sensitive material  106  can define an aperture  202  above one of the highly protected components  108 . A heat sink  302  can be thermally coupled to the highly protected component  108  through the aperture. The heat sink  302  can extend outward from the aperture above the tamper sensitive material  106  to dissipate heat from the highly protected component  108 . 
         [0024]      FIG. 2  is a top view of the PCB  102  and the tamper sensitive material  106 . As shown, the aperture  202  corresponds to a first component  204  of the highly protected components  108 . In an example, the first component  204  is a chip that generates a significant amount of heat (e.g., a processing unit). The aperture  202  can have a size that is approximately the size of an adjacent surface of the chip. In particular, the aperture  202  can be sized large enough such that sufficient contact can be made with the surface of the chip  204  to enable thermal conduction. The aperture  202 , however, can be sized small enough such that access to the interior of the enclosure formed by the tamper sensitive material  106  is difficult or impossible through the aperture  202 . Along with having a size the corresponds with the size of the aperture  202 , the tamper sensitive material  106  can be disposed such that the aperture  202  is close to the surface of the first component  204 . This can further limit the ability to access the interior of the enclosure formed by the tamper sensitive material  106 . In an example, the aperture  202  can be within a range of 0 to 5 millimeters from the surface of the first component  204 . The tamper sensitive material  106  can also include one or more apertures  206  that enable features  112  to extend through and contact sensors  110 . In an example, the one or more apertures  206  are sized corresponding to the one or more features  112 . 
         [0025]      FIG. 3  is a cross-sectional view of the electronic device  100 . As shown, the heat sink  302  can extend through the aperture  202  to thermally couple with the first component  204 . Heat flowing into the heat sink  302  from the first component  204  can be dissipated outside of the enclosure via fins of the heat sink  302 . In an example, a thermal interface material  304  can be disposed between the heat sink  302  and the first component  204  to aid in heat transfer. The heat sink  302  can be formed of any suitable material including copper, aluminum, graphene, or other material. 
         [0026]      FIG. 4  is a block diagram of example electronic components for the electronic device  100 . As mentioned above, the electronic device  100  can include highly protected components  108  that are protected by the tamper sensitive material  106  and less protected components  402  that are protected by the housing  104 , but not by the tamper sensitive material  106 . In an example, the highly protected components  108  can include a cryptographic processor  404  coupled to one or more memory devices  406 . As mentioned above, the one or more memory devices  406  can have data such as a cryptographic key stored therein. The cryptographic key can be provided to the cryptographic processor  404  and used to encrypt and decrypt data. In an example, the one or more memory devices  406  can include static random access memory (SRAM). The highly protected components  108  can also include a battery  408  coupled to the SRAM. The battery  408  can maintain the data within the SRAM when external power (e.g., line power) is not applied to the electronic device  100  and/or when the electronic device  100  is powered off. Accordingly, the data (e.g., the cryptographic key) within the SRAM can be maintained without needing to be repeatedly externally loaded into the electronic device  100 . Moreover, holding the data in SRAM can enable the data to be effectively zeroized. That is, the data in the SRAM can be zeroized by removing power to the SRAM. Accordingly, upon detection of tampering with the electronic device  100 , power can be removed from the SRAM thus zeroizing the data in the SRAM. Moreover, freezing of the electronic device  100  in an attempt to access the data will also result in power loss to the SRAM, thereby zeroizing the data therein. In some examples, the SRAM can include temperature sensors that automatically zeroize the data upon detecting a temperature reading out of band. 
         [0027]    The highly protected components  108  can also include security electronics  410  coupled to control connection of the battery  408  to the one or more memory devices  406 . The security electronics  410  can be configured to cut off power to the one or more memory devices  406  upon detection of tampering with the electronic device  100 . The security electronics  410  can be coupled to the tamper sensitive material  106  in order to detect tampering. In an example, a Wheatstone bridge can be coupled to the tamper sensitive material  106  to sense a change in state in the tamper sensitive material  106 . The security electronics  410  can also be coupled to the one or more sensors  110  in order to zeroize the data in the one or more memory devices  406  if the one or more sensors  110  detect separation of the tamper sensitive material  106  from the PCB  102 . Accordingly, the highly protected components  108  can be configured to implement secret cryptographic functions which are protected from physical access. Thus, the electronic device  100  can be provided to a potentially unfriendly individual and still provide secure cryptographic functions. 
         [0028]    In an example, the electronic device  410  can be configured to be coupled to a mass storage device  412 . The mass storage device  412  can hold encrypted data. The electronic device  410  can be configured to send data between the cryptographic processor  404  and the mass storage device  412 . Data from the mass storage device  412  can be decrypted by the cryptographic processor  404  and can be provided to the less protected components  402 . Additionally data to be stored on the mass storage device  412  can be provided by the less protected components  402 , encrypted by the cryptographic processor  404 , and stored on the mass storage device  412 . Accordingly, the data stored on the mass storage device  412  can be protected from unauthorized access. 
         [0029]    In an example, the less protected electronics  402  can include electronic components to perform other less secretive functions of the electronic device. For example, the less protected electronics  402  can include a general purpose processor (e.g., a CPU, microprocessor) coupled to a memory device having instructions thereon for implementing the functions of the electronic device. 
         [0030]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

Technology Category: 4