Abstract:
Various embodiments of the present disclosure provide systems and methods for securing electronic devices, such as financial payment terminals, to protect sensitive data and prevent unauthorized access to confidential information. In embodiments, this is achieved without having to rely on the availability of backup energy sources. In certain embodiments, tampering attempts are thwarted by using a virtually perfect PUF circuit and PUF-generated secret or private key within a payment terminal that does not require a battery backup system and, thus, eliminates the cost associated with common battery-backed security systems. In certain embodiments, during regular operation, sensors constantly monitor the to-be-protected electronic device for tampering attempts and physical attack to ensure the physical integrity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to and claims the priority benefit of co-pending and commonly-assigned U.S. Provisional Patent Application No. 62/362,804, titled “Systems and Methods for a Secure Payment Terminal without Batteries,” naming as inventors Robert Michael Muchsel and Gregory Guez, and filed Jul. 15, 2016, which application is hereby incorporated herein by reference in its entirety. 
     
    
     A. TECHNICAL FIELD 
       [0002]    The present disclosure relates to secure electronic systems and, more particularly, to systems and methods for protecting sensitive data in financial payment terminals to prevent unauthorized access. 
       B. DESCRIPTION OF THE RELATED ART 
       [0003]    Financial payment terminal devices process millions of transactions every day. Due to the risk and cost associated with exposure of payment information (e.g., credit card information), payment terminals must meet rigorous security standards to be accepted by banks, issuers, and credit card companies that require that critical information be encrypted at all times, and that secret keys be deleted in the event the terminal is attacked by potential intruders. 
         [0004]    Traditionally, this means that active components in the terminal have to continuously and actively monitor for signs of intrusion, and that secret keys and other sensitive information usually stored in memory devices within a computer system are erased from volatile memory upon detecting signs of a potential attack. Wiping the decryption key and/or the encryption memory renders the attack futile, as it makes it impossible for potential intruders to decipher the encrypted information and, thus, prevents capture of secret information by adversaries. 
         [0005]    Since volatile memory has to be employed, typically, a backup battery is necessary to provide continuous power to hold the decryption key in memory, for example, in circumstances when system power becomes temporarily or permanently unavailable, such as during transport or for portable payment terminals. In addition, security monitoring systems containing protective electronic meshes and other active parts are electrically operated and designed to detect physical tampering in situations when the financial terminal is powered down or experiences an unexpected power outage. In other words, a continuously active monitoring system remains in control of the physical integrity of the device. 
         [0006]    In addition, payment terminals and other devices containing secure microcontrollers that use battery-backed security monitoring systems have an average battery lifetime of about seven years. This is appropriate in most instances as hardware security modules are generally obsolete and replaced within that time period, such that the battery lifetime exceeds the actual operating time of the device in the field. 
         [0007]    However, devices with rather long lifetimes, such as smart meters, are expected to operate in the field for 30 years or more and practically with little or no maintenance at all. Given that even the most advanced batteries have a less than 10-year lifetime, this shortcoming renders protection of these devices ineffective once their batteries require replacement and power must be interrupted for a certain period of time to perform maintenance work. Similarly, for industrial devices that are located in remote places, such as oil or gas pipelines that are designed to operate as no-maintenance devices, replacing batteries in the field is not a viable solution due to the extremely high maintenance and support costs and, more importantly, security issues associated with powering down and opening a secure device that is intended to remain unopened. 
         [0008]    Currently, no practical solutions exist to ensure around-the-clock protection for high-security and long-life devices. Once the device is shut down, it is exposed and there is no security at all. Furthermore, energy sources, such as backup batteries, can add significant cost to the system for various reasons including increased component cost, maintenance cost due to limited battery lifetime, susceptibility to environmental factors, and the cost of obtaining proper certification (e.g., for use in airplanes). 
         [0009]    Some existing approaches reduce power consumption by an order of magnitude or more, e.g., by re-engineering intrusion sensors and memory components. More advanced approaches utilize active energy harvesting methods that power the intrusion sensors and the key memory. However, even the most sophisticated approaches are not always practical as they rely on the presence of energy sources, such as temperature gradients, to ensure uninterrupted and continuous power, which may not always be available. 
         [0010]    What is needed are systems and methods that provide a high level of uninterrupted security that prevents unauthorized access to sensitive data without the cost associated with common battery-backed security systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    References will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments. 
           [0012]      FIG. 1  is a general illustration of a conventional process for generating and using a secret key in a battery-backed up financial payment terminal. 
           [0013]      FIG. 2  is a flowchart of an illustrative process for generating and using a secret key in a secure system that does not require a battery backup, according to various embodiments of the present disclosure. 
           [0014]      FIG. 3  depicts a block diagram of a PUF-based security system that does not require a battery backup, in accordance with embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. Furthermore, one skilled in the art will recognize that embodiments of the present invention, described below, may be implemented in a variety of ways, such as a process, an apparatus, a system, a device, or a method on a tangible computer-readable medium. 
         [0016]    Components, or modules, shown in diagrams are illustrative of exemplary embodiments of the invention and are meant to avoid obscuring the invention. It shall also be understood that throughout this discussion that components may be described as separate functional units, which may comprise sub-units, but those skilled in the art will recognize that various components, or portions thereof, may be divided into separate components or may be integrated together, including integrated within a single system or component. It should be noted that functions or operations discussed herein may be implemented as components. Components may be implemented in software, hardware, or a combination thereof. 
         [0017]    Furthermore, connections between components or systems within the figures are not intended to be limited to direct connections. Rather, data between these components may be modified, re-formatted, or otherwise changed by intermediary components. Also, additional or fewer connections may be used. It shall also be noted that the terms “coupled,” “connected,” or “communicatively coupled” shall be understood to include direct connections, indirect connections through one or more intermediary devices, and wireless connections. 
         [0018]    Reference in the specification to “one embodiment,” “preferred embodiment,” “an embodiment,” or “embodiments” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention and may be in more than one embodiment. Also, the appearances of the above-noted phrases in various places in the specification are not necessarily all referring to the same embodiment or embodiments. 
         [0019]    The use of certain terms in various places in the specification is for illustration and should not be construed as limiting. A service, function, or resource is not limited to a single service, function, or resource; usage of these terms may refer to a grouping of related services, functions, or resources, which may be distributed or aggregated. Furthermore, the use of memory, database, information base, data store, tables, hardware, and the like may be used herein to refer to system component or components into which information may be entered or otherwise recorded. 
         [0020]    In this document the terms “key,” “secret key,” and “secret” are used interchangeably as are the terms “mesh, mesh envelope, and mesh circuit.” The term “secure device” includes secure microcontrollers, secure storage devices, and other secure elements recognized by one of skilled in the art. 
         [0021]    It shall be noted that: (1) certain steps may optionally be performed; (2) steps may not be limited to the specific order set forth herein; (3) certain steps may be performed in different orders; and (4) certain steps may be done concurrently. 
         [0022]    Furthermore, while embodiments described herein are described in the context of financial payment terminals, one skilled in the art shall recognize that the teachings of the present disclosure are not limited to payment terminals and may equally be applied to protect other forms of secure information, e.g., in the military, access control, IP protection, health, and medical fields, that may take advantage of the principles herein and be securely implemented without resorting to backup batteries. 
         [0023]      FIG. 1  is a general illustration of a conventional process for generating and using a secret key in a battery-backed up financial payment terminal. Process  100  for generating and using a secret key in a battery-backed payment terminal starts at step  102 , generally, as soon as a battery is attached to the payment terminal to start the life cycle. The event of the payment terminal being energized for the first time is known as its “first birthday.” 
         [0024]    At step  104 , sensors, such as motion sensors that are embedded in the payment terminal, are activated. 
         [0025]    At step  106 , a secret key is generated and the system enters into background mode  108  in which a backup battery activates the sensors of system  100  without activating, at the same time, system components that are intended to process financial transactions. 
         [0026]    In background mode  108 , the sensors are typically queried at a relatively reduced frequency mainly to conserve battery power. 
         [0027]    Once, at step  110 , main power is applied to the payment terminal, the system enters into active mode  112 , and both sensors and system components become fully functional. 
         [0028]    In embodiments, the system returns to background mode  108  in response to a loss of main power, but does not perform any power-hungry operations until main power is restored, at step  110 . 
         [0029]    If, while the system is an active mode  112  a security breach is detected, then, at step  114 , the encryption key and/or other secrets are permanently erased from the memory device within the terminal, or the memory device is irreversibly destroyed, and the system is shut down, at step  120 . Similarly, if, while the system is in background mode  108  and either a security breach or a loss of battery power is detected, the process deletes the key and/or other secrets, at step  114 , and shuts down the terminal, at step  120 . 
         [0030]    In short, system  100  cycles between background mode  108  and active mode  112  where the terminal actively performs tasks, unless a security breach or loss of battery power is detected, in which cases the terminal shuts down. 
         [0031]    In practice, this process is implemented in a financial terminal that uses, for example, three power sources: 1) a USB power source, 2) a relatively large lithium battery, and 3) a coin cell. The terminal generally operates on USB power as its main source of power. Once USB power becomes temporary or permanently unavailable, the terminal switches to the lithium battery or, as a last resort, to the coin cell to continue to power the protective sensors to keep the secrets alive in volatile memory until the voltage in the coin cell falls to a level that no longer can support the protective sensors, or until the system is manually restored. 
         [0032]    System  100  depends on the backup battery to power active monitoring and protection circuits. Furthermore, system  100  depends on the use of volatile memory, so that secrets can be erased quickly in the event of an intrusion attempt. Without the backup battery, the secrets would be exposed to the sophisticated attacker, who may access system  100 , perform circuit modifications without being detected, such that after the device is powered back up, there will be no trace indicating that the device has been invaded and manipulated. 
         [0033]    Therefore, it would be desirable to have systems and methods that provide a high level of security even in scenarios of a power outage without having to rely on common battery-backed security systems. 
         [0034]      FIG. 2  is a flowchart of an illustrative process for generating and using a secret key in a secure system that does not require a battery backup, according to various embodiments of the present disclosure. Process  200  for generating and using a secret key starts at step  202  when main power is applied to a system, such as a financial payment terminal. 
         [0035]    At step  204 , protective sensors that continuously monitor the system in regular operation are energized to prevent physical access to a secret key, e.g., an encryption key, that is generated, at step  206 , e.g., by using a PUF circuit or any other circuit that by design provides non-discoverable, unique, and random values that may be used as a keying source. 
         [0036]    Examples of systems and methods for suitable PUF circuits may be found in co-pending and commonly-owned U.S. Pat. App. No. 62/240,991, filed on Oct. 13, 2015, entitled “SYSTEMS AND METHODS FOR STABLE PHYSICALLY UNCLONABLE FUNCTIONS,” and listing Sung Ung Kwak as inventor (Docket No. 20057-1981P) and patent application. Ser. No. 14/480,129, filed on Sep. 8, 2014, entitled “SYSTEMS AND METHODS FOR STABLE PHYSICALLY UNCLONABLE FUNCTIONS,” and listing Pirooz Parvarandeh and Sung Ung Kwak as inventors (Docket No. 20057-1842), which patent documents are incorporated by reference herein in their entirety and for all purposes. 
         [0037]    At step  208 , the system enters into a state at which both sensors and system components are activated. The system performs regular tasks of encryption, authentication, and the like. In embodiments, PUF-generated secret key or a derivation thereof is used, for example, to obtain information for a setup process or to decrypt encrypted information that is stored in non-volatile memory (e.g., flash memory). In this active mode  208 , a shield (e.g., an active mesh) may be used to protect data that is being transferred and available for processing in unencrypted format. 
         [0038]    In embodiments, a second key is derived from a PUF-generated key that serves as a master key that may be used to encrypt the second key that may then be stored in non-volatile memory and, thereby, aid in minimizing the use and exposure of the master key itself. 
         [0039]    Once a security breach, a loss of power, or the presence of a predetermined event is detected, the system may delete the key and/or secrets or the entire system may be shut down. In embodiments, the PUF circuit is physically destroyed (e.g., by applying heat), for example, after a number of attempts to compromise system security have been detected. 
         [0040]    In embodiments, once the system is shut down at step  212 , the PUF-generated number is no longer available and, as a result, there is no key present that could be discovered, stolen, and used to access protected information. 
         [0041]    Upon restoring main power, at step  202 , process  200  may resume, at step  204 , with energizing the sensors and using the PUF circuit to re-generate, at step  206 , the secret key to its original value. 
         [0042]    Aspects of the present patent document are directed to information handling systems. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, calculate, determine, classify, process, transmit, receive, retrieve, originate, route, switch, store, display, communicate, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer (e.g., desktop or laptop), tablet computer, mobile device (e.g., personal digital assistant (PDA) or smart phone), server (e.g., blade server or rack server), a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, touchscreen and/or a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components. 
         [0043]      FIG. 3  depicts a block diagram of a PUF-based security system  300  that does not require a battery backup, in accordance with embodiments of the present disclosure. System  300  comprises processing unit  302 , crypto engine  312 , system memory  304 , peripheral interfaces  308 , Physically Unclonable Function (PUF)  310 ; and shield  320 , which may be an active mesh designed to detect physical intrusion attempts into any of the devices within system  300  that may comprise sensitive data. 
         [0044]    It will be understood that the functionalities shown for system  300  may operate to support various embodiments of any information handling system that may be differently configured and include different components as those shown in  FIG. 3 . In embodiments, system  300  is embedded in a point-of-sale-terminal that may create, store, encrypt, authenticate, and transmit sensitive data, such as confidential payment-related banking information and encryption keys. As illustrated in  FIG. 3 , processing unit  302  provides computing resources and may be implemented with any secure microcontroller known in the art. It may comprise a graphics processor and/or a floating point coprocessor for mathematical computations. 
         [0045]    System  300  includes Physically Unclonable Function (PUF)  310  circuit that is integrated with system  300 . In general, a PUF takes advantage of minute but measurable manufacturing variations in physical semiconductor devices. These characteristic variations include variations in gate oxide thickness, concentrations of doping materials, and tolerances in geometrical dimensions that result from less than perfect semiconductor manufacturing processes that the semiconductor device (e.g., a MOSFET) undergoes. In various applications, the variations are used to produce sequences of random, but relatively repeatable data that may then be used to identify a device or perform other authentication functions. The repeatability of a random, device-unique number generated by existing PUFs is about 80%, which is sufficiently high for authentication applications as such level of accuracy suffices to generate a relatively unique response from the PUF circuit in that it becomes very unlikely that another PUF circuit is capable of correctly generating the same amount of bits due to the fact that a very small change at the input of a PUF circuit generates a very large change at the output. For example, changing the single bit of the circuit results in about a 50% variation in the output signal, i.e., the PUF becomes unreliable. 
         [0046]    Further, the circuit response significantly and unpredictably changes when physical conditions (e.g., electrical conduction properties) of the PUF circuit even slightly change, e.g., after physical impact, or when the system containing the PUF circuit is probed or altered, which typically causes irreversible damage to the physical structure. 
         [0047]    Embodiments of the present disclosure employ PUF circuit  310  that generates a random, device-unique, but highly repeatable value (e.g., 1 ppb error rate), for example, via by using Repeatable Tightly Coupled Unique Identification Elements as disclosed, for example, in above-mentioned U.S. Patent Application No. 62/240,991. Unlike in existing designs, this highly repeatable value may be a number that can be used to reliably and repeatably generate a cryptographic key. 
         [0048]    In embodiments, the key or secret is stored in a volatile memory device (not shown in  FIG. 3 ) that may be internal or external or external to any of the components shown in  FIG. 3 . The volatile memory holds the key that, upon system  300  detecting a power outage, is automatically deleted as the volatile memory need not be supported by a battery backup system or another source of alternative energy in the event mains power is interrupted. As a result of there being no key present, unlike prior art designs, no protection and no battery is needed. 
         [0049]    In embodiments, cryptographic engine  312  may implement any strong cryptographic algorithm recognized by one of skill in the art, e.g., symmetric algorithms, such as Advanced Encryption Standard, or public key cryptography, such as RSA or Elliptic Curve Cryptography. It is understood that cryptographic engine  312  may process a secret together with other data or software to provide functional protection. 
         [0050]    In embodiments, rather than relying on software, cryptographic engine  312  is implemented as a hardware engine that performs cryptographic operations, such as data encryption, data decryption and integrity checks. The hardware engine may facilitate increased reaction to fault attacks and enhanced performance for data encryption or decryption. 
         [0051]    In embodiments, a PUF-generated key is loaded into and stored in cryptographic engine  312 . Upon detection of a security breach, e.g., a tamper attempt, the key is instantly erased from volatile memory. The presented embodiments advantageously also eliminate the need to store keys in non-volatile memory and, thus, renders system  300  immune to reverse engineering and other advanced methods by sophisticated attackers not further discussed herein. 
         [0052]    System  300  may include system memory  304 , which may be random-access memory (RAM) and read-only memory (ROM). It is noted that any part of system  300  may be implemented in an integrated circuit. Any number of controllers and peripheral devices  306  may be provided, as shown in  FIG. 3 . 
         [0053]    Peripheral interfaces  308  represent interfaces to various input device(s), such as a keyboard, mouse, or stylus. System  300  may also include a storage controller for interfacing with one or more storage devices each of which includes a storage medium such as magnetic tape or disk, or an optical medium that might be used to record programs of instructions for operating systems, utilities and applications which may include embodiments of programs that implement various aspects of the present invention. Storage device(s) may also be used to store processed data or data to be processed in accordance with the invention. System  300  may also include a display controller for providing an interface to a display device, which may be a cathode ray tube (CRT), a thin film transistor (TFT) display, or other type of display. The computing system  300  may also include a printer controller for communicating with a printer. A communications controller may interface with one or more communication devices, which enables system  300  to connect to remote devices through any of a variety of networks including the Internet, an Ethernet cloud, an FCoE/DCB cloud, a local area network (LAN), a wide area network (WAN), a storage area network (SAN) or through any suitable electromagnetic carrier signals including infrared signals. 
         [0054]    In the illustrated system, all major system components may connect to a bus  360 , which may represent more than one physical bus. However, various system components may or may not be in physical proximity to one another. For example, input data and/or output data may be remotely transmitted from one physical location to another. In addition, programs that implement various aspects of this invention may be accessed from a remote location (e.g., a server) over a network. Such data and/or programs may be conveyed through any of a variety of machine-readable medium including, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media; and hardware devices that are specially configured to store or to store and execute program code, such as application specific integrated circuits (ASICs), programmable logic devices (PLDs), flash memory devices, and ROM and RAM devices. 
         [0055]    Embodiments of the present invention may be encoded upon one or more non-transitory computer-readable media with instructions for one or more processors or processing units to cause steps to be performed. It shall be noted that the one or more non-transitory computer-readable media shall include volatile and non-volatile memory. It shall be noted that alternative implementations are possible, including a hardware implementation or a software/hardware implementation. Hardware-implemented functions may be realized using ASIC(s), programmable arrays, digital signal processing circuitry, or the like. Accordingly, the “means” terms in any claims are intended to cover both software and hardware implementations. Similarly, the term “computer-readable medium or media” as used herein includes software and/or hardware having a program of instructions embodied thereon, or a combination thereof. With these implementation alternatives in mind, it is to be understood that the figures and accompanying description provide the functional information one skilled in the art would require to write program code (i.e., software) and/or to fabricate circuits (i.e., hardware) to perform the processing required. 
         [0056]    It shall be noted that embodiments of the present invention may further relate to computer products with a non-transitory, tangible computer-readable medium that have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind known or available to those having skill in the relevant arts. Examples of tangible computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media; and hardware devices that are specially configured to store or to store and execute program code, such as application specific integrated circuits (ASICs), programmable logic devices (PLDs), flash memory devices, and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Embodiments of the present invention may be implemented in whole or in part as machine-executable instructions that may be in program modules that are executed by a processing device. Examples of program modules include libraries, programs, routines, objects, components, and data structures. In distributed computing environments, program modules may be physically located in settings that are local, remote, or both. 
         [0057]    One skilled in the art will recognize no computing system or programming language is critical to the practice of the present invention. One skilled in the art will also recognize that a number of the elements described above may be physically and/or functionally separated into sub-modules or combined together. 
         [0058]    It shall be noted that elements of the claims, below, may be arranged differently including having multiple dependencies, configurations, and combinations. For example, in embodiments, the subject matter of various claims may be combined with other claims. 
         [0059]    It will be appreciated to those skilled in the art that the preceding examples and embodiment are exemplary and not limiting to the scope of the present invention. It is intended that all permutations, enhancements, equivalents, combinations, and improvements thereto that are apparent to those skilled in the art upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present invention.