Patent Publication Number: US-11051126-B2

Title: Systems and methods for high-assurance indoor proximity and location

Description:
BACKGROUND OF THE INVENTION 
     Technical Field 
     The disclosed embodiments relate in general to positioning systems and, more specifically, to systems and methods for high-assurance indoor proximity and location. 
     Description of the Related Art 
     A long-standing problem in the art has been fast and accurate determination of indoor location. A variety of hardware and software techniques have been created and, especially in recent years, solutions have been proposed that are both reliable and easy to deploy. Many of these technologies enable everyday devices like smartphones and tablets to determine their indoor position. In fact, technologies like APPLE®&#39;s iBEACON framework are beginning to see large adoption, deployment, and use. As a result, a technology foundation is being laid for an explosion of indoor location-enabled applications. 
     For a broad class of applications, accurate location information provides context to assist or enhance the user&#39;s experience. These include points of interest applications, mapping tools, and social presence sharing applications. While an inaccurate or manipulated location would impact the usefulness of these applications, it would not be harmful from the perspective of the service provider. However, there are many other applications in which the accuracy and trustworthiness of the location is integral to the application itself. These include room access, inventory control, and document access solutions whose decisions to permit or deny access to physical or virtual objects have a contextual dimension that includes the user&#39;s physical location. 
     There has been a significant amount of past research and development that has focused on trusted localization. However, much of this work has explored point solutions. For instance, solutions have been developed to provide anonymous but verifiable location check-ins for location-based services, context-based proofs of compresence that piggyback on existing infrastructure, and systems for creating and verifying secure proofs of (coarse) location in multi-stakeholder WIFI® or cellular environments. U.S. Pat. No. 9,491,588, incorporated herein by reference, describes a solution that affords a certain degree of location assurance using a novel protocol that encodes location and time information into a BLE (BLUETOOTH® low energy) beacon-based location framework. The protocol protects against replay attacks, but is still susceptible to attacks in which two or more users collude to produce a location proof for some user that differs from that user&#39;s physical location. 
     Therefore, as would be appreciated by persons of ordinary skill in the art, new and improved systems and methods for high-assurance indoor proximity and location are highly desirable. 
     SUMMARY OF THE INVENTION 
     The embodiments described herein are directed to methods and systems that substantially obviate one or more of the above and other problems associated with conventional localization techniques. 
     In accordance with one aspect of the inventive concepts described herein, there is provided a computer-implemented method, the method being performed in a computerized system incorporating a central processing unit, a localization signal receiver and a memory, the computer-implemented method involving: receiving at least one localization signal using the localization signal receiver; measuring a strength of the received localization signal; determining whether the computerized system is co-located with an anchor device; and if the computerized system is determined to be co-located with the anchor device, determining a location based at least on the measured strength of the received localization signal. 
     In one or more embodiments, determining whether the computerized system is co-located with the anchor device involves receiving a first message including a key from the anchor device; transmitting a second message including at least the received key back to the anchor device; and analyzing, at the anchor device, a timing of the first message in relation to a timing of the second message. 
     In one or more embodiments, the computerized system is determined to be co-located with the anchor device if a time lapsed between the first message and the second message does not exceed a predetermined threshold. 
     In one or more embodiments, the key is a randomly generated nonce. 
     In one or more embodiments, the second message is signed using a private cryptographic key associated with the computerized system and wherein the anchor device validates the second message using a public key associated with the computerized system. 
     In one or more embodiments, receiving the first message and transmitting the second message are performed via a near field communication (NFC) protocol. 
     In one or more embodiments, the second message further includes the measured strength of the received localization signal. 
     In one or more embodiments, the anchor device transmits a third message to a server, the third message including at least the second message and a location proof of the anchor device. 
     In one or more embodiments, the third message is signed using a private cryptographic key associated with the anchor device and wherein the server validates the third message using a public key associated with the anchor device. 
     In one or more embodiments, the key is unique. 
     In one or more embodiments, the received localization signal is provided by a beacon disposed in a room of a building. 
     In one or more embodiments, the anchor device is a trusted device including a trusted execution environment. 
     In one or more embodiments, determining a location based at least on the measured strength of the received localization signal is performed on a server and wherein the server is configured to transmit a location proof to the computerized system. 
     In one or more embodiments, the location proof is transmitted to the computerized system via the anchor device. 
     In one or more embodiments, the computerized system executes a user application and wherein the location proof is provided to the user application. 
     In one or more embodiments, the method further involves anchoring the anchor device. 
     In one or more embodiments, anchoring the anchor device involves receiving, at the anchor device, at least one second localization signal; measuring a strength of the received second localization signal; and determining a location of the anchor device based at least on the measured strength of the received localization signal. 
     In one or more embodiments, the determining a location of the anchor device based at least on the measured strength of the received second localization signal is performed on a server and wherein the server is configured to transmit a location proof to the anchor device. 
     In one or more embodiments, the method further involves detecting a motion of the anchor device and invalidating the location proof of the anchor device based on the detected motion. 
     In one or more embodiments, the anchor device incorporates an accelerometer and wherein the motion of the anchor device is detected using the accelerometer. 
     In one or more embodiments, the location proof of the anchor device is invalidated when the detected motion exceeds a predetermined threshold. 
     In one or more embodiments, determining whether the computerized system is co-located with an anchor device is performed periodically. 
     In accordance with another aspect of the inventive concepts described herein, there is provided a non-transitory computer-readable medium embodying a set of computer-executable instructions, which, when executed in connection with a computerized system incorporating a central processing unit, a localization signal receiver, a display and a memory, cause the computerized system to perform a method involving: receiving at least one localization signal using the localization signal receiver; measuring a strength of the received localization signal; determining whether the computerized system is co-located with an anchor device; and if the computerized system is determined to be co-located with the anchor device, determining a location based at least on the measured strength of the received localization signal. 
     In accordance with yet another aspect of the inventive concepts described herein, there is provided a computerized system incorporating a central processing unit, a localization signal receiver and a memory, the memory storing a set of computer-readable instructions causing the computerized system to perform a method involving: receiving at least one localization signal using the localization signal receiver; measuring a strength of the received localization signal; determining whether the computerized system is co-located with an anchor device; and if the computerized system is determined to be co-located with the anchor device, determining a location based at least on the measured strength of the received localization signal. 
     Additional aspects related to the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Aspects of the invention may be realized and attained by means of the elements and combinations of various elements and aspects particularly pointed out in the following detailed description and the appended claims. 
     It is to be understood that both the foregoing and the following descriptions are exemplary and explanatory only and are not intended to limit the claimed invention or application thereof in any manner whatsoever. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the inventive concepts. Specifically: 
         FIG. 1  illustrates an exemplary logical diagram of an embodiment of a high assurance localization system described herein. 
         FIG. 2  illustrates an exemplary embodiment of a secure beacon. 
         FIG. 3  illustrates an exemplary control flow for establishing a location proof between the anchor device and the secure server. 
         FIG. 4  illustrates an exemplary overall control flow for establishing a high assurance location proof. 
         FIG. 5  illustrates an exemplary control flow for (optional) BLE proximity checking with client device. 
         FIG. 6  illustrates an exemplary embodiment of a computerized mobile system that could be used as the client device or anchor device in connection with the localization system illustrated in  FIG. 1 . 
         FIG. 7  illustrates an exemplary embodiment of a computerized server system, which could be used, for example, as the central server of the localization system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference will be made to the accompanying drawing(s), in which identical functional elements are designated with like numerals. The aforementioned accompanying drawings show by way of illustration, and not by way of limitation, specific embodiments and implementations consistent with principles of the present invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other implementations may be utilized and that structural changes and/or substitutions of various elements may be made without departing from the scope and spirit of present invention. The following detailed description is, therefore, not to be construed in a limited sense. Additionally, the various embodiments of the invention as described may be implemented in the form of a software running on a general purpose computer, in the form of a specialized hardware, or combination of software and hardware. 
     The below description focuses on providing a technology framework for creating secure, location-based applications. To address the above and other problems associated with the conventional technology, one or more embodiments described herein implement a system and method for performing high assurance proofs of proximity and location that requires significantly less infrastructure burden compared to previously proposed methods. In one or more embodiments, to achieve the aforesaid goal of performing high assurance proofs of proximity and location, there is provided a set of protocols and a specialized hardware device that leverage secure localization technologies with new cryptographic techniques to assert a device, or set of devices, are at, and stay at, a specific indoor location. In various embodiments, this technology can be used to support several secure location applications, such as secure document access. 
     In one or more embodiments, there is provided a technology solution that can allow users to access secure information on commodity computation devices (e.g., tablets and smartphones) without a heavy infrastructure burden. In various embodiments, the described technology consists of a collection of software services that run on end-user devices, services on network accessible servers (e.g., cloud), and a specialized device that provides high-assurance location services atop a tamper resistant, trusted computation platform. 
     To illustrate the need for the described technology, consider the simple case of location-based document access. For instance, specifying that an electronic document is only viewable when the viewing device is in a specific physical space (e.g., a particular conference room in an office building.) This application must leverage underlying location technologies that have the accuracy and precision to localize the device in the appropriate room, and must be trustworthy in that determination. For commodity, off-the-shelf devices this assertion is difficult to provide. The device itself is not a trusted computation platform, nor are the sensors and/or network used to capture and transmit information used to perform a location determination. 
     The embodiments described herein provide greater assurances on the location estimation and the computational infrastructure that is used to sense, compute, and replay this estimation. While there are infrastructure-heavy solutions to high-assurance device localization (e.g., as described in the previous invention), the described techniques provide a lightweight and flexible solution to this problem that is capable of supporting a wide range of high assurance applications. 
     High Assurance Localization System Architecture 
       FIG. 1  illustrates an exemplary logical, diagram of an embodiment of a high assurance localization system  100  described herein. In one exemplary embodiment, the high assurance localization system  100  incorporates several components, including: a deployment of multiple cloud connected beacons  101 , a cloud beacon agent (CBA)  105 , a central server  104 , a location classification engine (LCE)  112 , executing on the central server  104 , and a client device  102 . The client device  102  runs both client location services  103  and client anchor services  106 . Finally, the high assurance localization system  100  incorporates a specialized device, called an anchor device  107 . The anchor device  107  executes location services  108 , anchor services  109  and environmental services  110 . Each of the above components of the high assurance localization system  100  will be described in detail below. In one or more embodiments, the client device  102  may additionally execute a client application  111 . 
     Cloud-Connected Secure Beacons  101   
     In one or more embodiments of the high assurance localization system described herein location estimates are determined through the collection of signal strength measurements from a plurality of fixed beaconing devices  101 , shown in  FIG. 1 . While measurements from a variety of radios can be used, an embodiment of the described system  100  relies on BLUETOOTH® Low Energy devices, well known to persons of ordinary skill in the art, to maintain compatibility across a wide-range of existing devices. It should be noted, however, that other types of beaconing devices  101  may be used to facilitate location estimation and, therefore, the described system is not limited to any specific type or types of beaconing devices. 
       FIG. 2  illustrates an exemplary embodiment of a secure beacon  101  that is comprised of two hardware components—a BLUETOOTH® Low Energy (BLE) radio  201  and a WIFI® enabled system on a chip (SoC)  202 . In one or more embodiments, the SoC  202  communicates securely with a cloud based runtime engine (the Cloud Beacon agent (CBA)  105  ( FIG. 1 )) that allows its software and functionality to be updated at regular intervals. The SoC  202  device also controls the state of the BLUETOOTH® radio  201  through an ICT bus connection. In one exemplary embodiment, the beacon device  101  is powered by four AA 1.5V batteries that are power regulated to 3V output. Under normal use, this should power the beacon for at least a year. 
     In one or more embodiments of the localization system  100  described herein, the cloud beacon  101  operates in two modes: beacon mode and update mode. In the beacon mode, the system on a chip  202  is placed into sleep state and the BLUETOOTH® radio  201  is programmed to wake regularly (for example every 2000 ms) to transmit an iBEACON® compatible advertisement. In one embodiment, this advertisement contains three main segments: a UUID that associates the device to specific services or capabilities, major ID, and minor ID. The UUID is used to identify the beacon  101  as a beacon of the localization system  100 . The major ID is used to uniquely identify each beacon  101 . This ID is used by the location classification engine  103  along with the received signal strength of the beacon  101  to determine a device&#39;s location. In one embodiment, the classification engine  103  uses the major IDs of the beacons to classify the room-level location of the device. 
     Finally, the minor ID is used to provide cryptographic material used by the location authority, described in further detail below. The main function of the connected beacon is to be able to set and control the minor ID value to correctly transmit the cryptographic key used by the location authority. The classification engine  112  uses the minor IDs of the beacons to ensure the freshness of the advertisements to guard against replay or spoofing attacks. 
     In one or more embodiments, in the update mode, which occurs at fixed, but configurable intervals, the WIFI system on a chip (SoC)  202  connects to the CBA  105  to download new beaconing assignments. These include Minor ID based on a new cryptographic key, or new UUID/Major assignments to invalidate and reconfigure the overall location infrastructure. In this state, all the parameters of the iBEACON® advertisement can be updated. When the beacon  101  is deployed, this operation normally configures a new minor ID which is a new unique key provided by the location authority. 
     Location Classification Engine (LCE) 
     In one embodiment, the LCE provides a landmark-based location classification, well known in the art. In another embodiment, the LCE implements location estimation techniques that provide coordinate based location (X,Y,e) (either by using heuristics based on distance rather than location context, or through the projection of a coordinate location onto a map ontology to determine a landmark location). 
     In one or more embodiments, the location classification techniques utilized by the described system, are based on the ensemble learning method of boosting described, for example, in Freund, Y., Schapire, R.: A decision-theoretic generalization of on-line learning and an application to boosting. Journal of Computer and System Sciences 55(1), 119-139 (1997) and 11. Hastie, T., Tibshirani, R., Friedman, J., The Elements of Statistical Learning, Springer, New York, 2001. In contrast to more common matching methods such as described in Bolliger, P. Redpin—adaptive, zero-configuration indoor localization through user collaboration. In Proceedings of the ACM international workshop on Mobile entity localization and tracking in GPS-less environments, (MELT 2008), pp. 55-60, boosting provides similar classification accuracy without requiring the storage of a search data structure that grows with the training set size. Further, boosting performs most of the computation in offline training, allowing for classification runtime performance to be orders of magnitude faster compared to matching approaches, see for example Biehl, J. T., Cooper, M., Filby, G., Kratz, S. LoCo: A Ready-to-Deploy Framework for Efficient Room Localization using Wi-Fi. In Proceedings of the ACM Conference on Ubiquitous Computing (Ubicomp 2014). 
     In one or more embodiments, the location classification engines  103  and/or  108  seek to provide location relative to a discrete spatial quantization, or more generally rooms (e.g., personal office) or locations of interest (e.g., near a landmark in a large space). In one or more embodiments, for each discrete location, a binary classifier is constructed that outputs a score representing the probability that the RSSI scan vector S was observed in that room/location:
 
 F   room ( S )=Σ m α m   h   m ( S )
 
     In one or more embodiments, each per-room classifier combines “weak learners”, h m  according to the scalar weights α m . The weak learners are decision stumps that compare a scalar feature to a threshold θ m : 
     
       
         
           
             
               
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     In training, the thresholds θ m  are tuned to minimize error. The feature vector is defined to consist of elements X m  and is computed from each RSSI vector S below. 
     In one or more embodiments, given the observed RSSI vectors, the set of unique pairwise differences (margins) between the vectors&#39; elements is computed. For an environment with B total beacons, the resulting margin feature vectors have size 0.5·B·(B·1). Intuitively, these features express coarse order information for the pairs of beacons. The RSSI vector S∈   B  is transformed into a margin feature vector with elements:
 
 X   m   =S ( a   m )− S ( b   m ),
 
     for a m , b m  ∈ { 1 , . . . , B}. Missing RSSI values for specific beacons in the training set are set to a nominal value, R min  to indicate they were not visible to the mobile client  102 . Thus, the fact that specific beacons  101  are not visible at specific locations is incorporated into the features. 
     In one or more embodiments, the margin features computed from the training scans form the input to classifier training. Each scalar margin feature corresponds to a weak learner (h m ) available for inclusion in any per-room classifier F room (S). The training procedure identifies a location-specific set of weak learners that best discriminates that location from all others. The weak learners and their relative weights (α m  in the equation above) for each per-location classifier are learned in a greedy iterative procedure that optimizes error using a per-sample weighting over the training data, as described, for example in Hastie, T., Tibshirani, R., Friedman, J., The Elements of Statistical Learning, Springer, New York, 2001. 
     In one or more embodiments, for location determination, a one versus all formulation is used. The estimated room is simply the maximum scoring room among the set of per-room classifiers when applied to a test scan S test :
 
room*( S   test )=argMax room   F   room ( S   test )
 
     In one or more embodiments, only the required set of RSSI differences that were selected in classifier training are computed. These differences are compared to the thresholds (θ m ) and then combined linearly. 
     Central Server and Cloud Beacon Agent 
     In one or more embodiments, the central server  104  performs basic coordination activities between beacons  101 , cloud beacon agent(s)  105 , client device(s)  102 , and anchor device(s)  107 . In one or more embodiments, an important role of the central server  104  is to generate and maintain a set of cryptographic keys. These keys are used as part of the proof of location security protocol, discussed in details below. In one exemplary embodiment, at a prescribed interval, a new 16-bit cryptographic key is produced by the central server  104  for each beacon  101 . The aforesaid cryptographic keys are distributed by the central server  104  to the cloud beacon agent  105 , which in turn, creates a new advertisement profile for each beacon  101  that encodes the 16-bit cryptographic key in the advertisement&#39;s Minor ID field. These new advertisement profiles are then pushed to individual beacons  101  when they wake for update. The central server  104  maintains a list of current and recent keys that have been distributed to the beacons  101 . The central server  104  also serves as the location proof authority. When a client provides a scan record to the central server  104 , it can perform localization using the LCE as well as compare the Minor ID embedded cryptographic keys. In one or more embodiments, a third-party API is also provided by the central server  104 . With a unique API access key, external web applications can make REST-style requests for a location of the user device  102 . 
     In one or more embodiments, the basic method of high assurance location estimation is performed as follows: scan data is first collected by a client device  102  and/or anchor device  107  and passed to the central server  104 . The scan includes received signal strength (RSSI) measurements from beacons  101  with corresponding hardware IDs, which include per-beacon cryptographic keys previously distributed to the beacons  101  by the cloud beacon agent  105 . This scan data is sent to the central server  104  using encryption with a per-client cryptographic key, which is also available to the central server  104 . The central server  104  determines the location of the user device  102  based on the received information and returns a location ticket (proof) with the corresponding location information in both cases. The described scheme requires no modification to the beacon hardware, nor any additional client side processing. 
     Client Device Services 
     In one or more embodiments, in addition to the end-user application  111 , the client device  102  executes two additional services  106  and  103 . In one embodiment, the end-user application  111  may be a secure document viewer, which is configured to allow or deny access to a document based on user device&#39;s location. In another embodiment, the end-user application  111  may be a secure entry control application configured to open door locks based on user device&#39;s location. 
     In one embodiment, the client location service  103  is responsible for system-level location estimation activities. The client location service  103  periodically captures nearby location advertisements that include the UUID, Major ID, and Minor ID along with a measurement of the received signal strength (RSSI). Once a set of scan records is collected, the client location service  103  provides this information to the location classification engine (LCE). In various embodiments, the LCE can perform classification locally on the client device  102  or send the scan information to a server-based instance of the LCE  109 . 
     In one or more embodiments, the client anchor service  106  handles interaction with the anchor device  107 . Primarily, this communication is designed to enable a high-assurance location proof. In one embodiment, this involves the client device  102  initiating a connection with the anchor device  107  using a near field communication channel (for instance NFC for most devices). Over this channel, the anchor device  107  issues a challenge to the client device  102  that must be responded to within a predetermined time window (protocol of this exchange discussed below). In some embodiments, continuous ranging (using BLE) with a cryptographic minor payload (as discussed above) is used in combination with the location services  103  to provide a higher degree of assurance that the client device  102  stays within a close proximity to the anchor device  107 . 
     Anchor Device and Services 
     In one or more embodiments, the anchor device  107  is a specialized portable computation device. In one exemplary embodiment, it is comprised of an ARM-based computer, such as Raspberry Pi or DragonBoard, well known in the art and available commercially, WIFI®, BLE, NFC communication hardware, simple I/O (LED lights and LED display), and environmental sensors (accelerometer). As discussed in detail below, the anchor device  107  provides many different functions, which are implemented across three primary services. Similar to the client device  102 , a location service  108  of the anchor device  107  is responsible for monitoring the location of the anchor device  107 . As such, the location service  108  of the anchor device  107  collects the BLE scan information, estimates the location of the anchor device  107  (if done locally), and transmits that information (including the cryptographic minor values) to the central server  104 . The anchor services  109  provide local communication services over the BLE protocol for communicating directly with other anchor devices  107 , and, in some embodiments, monitoring the proximity of those other anchor devices  107  relative to itself. The corresponding protocol will be described in detail below. Finally, in one or more embodiments, the environmental services  110  use the environmental sensors on the anchor device  107  to monitor and determine when the anchor device  107  has been moved. For instance, in some use cases, detecting such motion (“breaking the anchor”) results in the location assurance provided by the anchor device  107  to be revoked. 
     Trusted Device Management 
     In one or more embodiments, to increase the trustworthiness of the anchor device  107 , existing security features present on the types of ARM-based platforms described above, which are used in implementing the anchor device  107 , are leveraged. Specifically, in one embodiment, the anchor device  107  uses a trusted execution environment (TEE) enabled by ARM TrustZone. In an alternative embodiment, the anchor device  107  uses an appropriate firmware, which is available on the DragonBoard. In yet another embodiment, the anchor device  107  uses a discrete TPM, available on Raspberry Pi, to ensure platform integrity and secure storage of cryptographic keys. These technologies allow for the secure generation, storage, and use of cryptographic keys needed by the anchor device  107 , thereby preventing the exfiltration of cryptographic material from the anchor device  107 . They further enable the use of trusted boot, which provides a cryptographic mechanism for ensuring the integrity of code running on the platform. In the case of the anchor device  107 , this would enable assurances that only an unmodified software image of the anchor device  107  could be loaded into the memory of the anchor device  107  to help limit the effects of tampering attacks carried out against the anchor device  107 . 
     Protocols 
       FIG. 1  discussed above further illustrates the communication paths between all components of the high assurance localization system  100  described herein. Specifically, in this figure, the used protocols are indicated by lines, including communication methods used, which are represented by different line types. As noted in the legend of  FIG. 1 , four different communication protocols are used: BLUETOOTH® low energy (BLE), inter-process communication on an individual device (IPC), Near field communication (NFC), and Transport layer security (TLS) over WIFI®. Now, the interaction of these system components with one another will be described in detail. 
     Anchoring the anchor device  107  involves interactions between the anchor device  107 , and a secure indoor localization service implemented by the central server  104 . In one embodiment, to bind the anchor device  107  to a physical location, the user simply places the anchor device  107  on a flat surface and presses an anchor button on the device. 
       FIG. 3  illustrates an exemplary control flow  300  for establishing a location proof between the anchor device  107  and the secure server  104 . First, at step  301 , the anchor device  107  determines its physical location by gathering an RSSI scan dataset from the BLE beacon infrastructure managed by the central server  104 . This scan dataset is then digitally signed by the anchor device  107  and passed to the central server  104  over a WIFI®, secured using the TLS protocol, see step  302 . The central server  104  verifies the digital signature on the RSSI scan dataset, checks that the rotating cryptographic codes broadcast by the BLE beacon infrastructure are current, classifies the anchor device&#39;s  107  location, and generates a digitally signed location proof containing a timestamp, the RSSI scan dataset used, the classified location, and the ID of the anchor device  107 , see step  303 . The resulting proof is then returned to the anchor device  107  over the existing TLS tunnel, see step  304 . At this point, a small LED readout on the side of the device will display the location encoded in the location proof. To accept this location, the user presses the anchor button again, thereby locking the anchor device  107  to this physical location. 
     At this point, the anchor device  107  is ready to participate in the construction of high-assurance proofs of location. The anchor device  107  also begins an environmental monitoring process in the background that leverages the attached accelerometer to determine whether the anchor device  107  has been moved. If the environmental monitoring procedure detects a motion of the anchor device  107 , the anchor device  107  un-anchors itself and invalidates its current location proof. In this state, it cannot assist in the creation of high-assurance location proof until the anchor device  107  is again anchored. In one or more embodiments, the anchor device  107  stores appropriate motion threshold(s) for determining if the current location proof should be invalidated, in the event the detected motion parameters(s) exceed such stored threshold(s). 
     The initial construction of the high-assurance proofs of location will now be described.  FIG. 4  illustrates an exemplary overall control flow  400  for establishing a high assurance location proof. In one or more embodiments, to create a high-assurance proof of authorization, the mobile device  102  may first leverage its location services framework to gather an RSSI scan dataset from the BLE beacons  101 , see step  401 . This device  102  is then placed upon an anchored anchor device  107  to enable NFC communication between the aforesaid two devices. The anchor services module  109  within the anchor device  107  generates a random number (n) (server nonce) and transfers it to the anchor services module  106  of the mobile device  102  via NFC, see step  402 . The mobile device  102  then creates a digitally-signed message containing a unique identifier for the device (IDD), the RSSI scan dataset (R), and the server nonce (n). This message is then returned to the anchor device  107  via NFC, see step  403 . 
     To complete the high assurance proof construction process, the anchor device  107  first performs timing check at step  404 , to verify that the time lapsed from the sending of the random number (n) in step  402  to the receiving of the aforesaid digitally-signed message in step  403  does not exceed a predetermined threshold to prevent spoofing. In addition, the nonce (n) received from the mobile device  102  in the aforesaid digitally-signed message may be verified. If the timing check is successful, the anchor device  107  subsequently digitally signs a message containing its unique identifies (IDA), the location proof that it obtained during the anchoring process (pfA), and the digitally-signed message generated by the client device  102  ([IDD, R, n]KD-1). This message is then transferred to the central server  104  via TLS, see step  405 . Prior to generating a location proof for the mobile device  102 , the central server  104  verifies that pfA is still valid, verifies that the mobile device  102  and anchor device  107  digital signatures are correct, classifies the device location from the RSSI dataset, and ensures that this classified location matches the location in pfA, se step  406 . In addition, the nonce (n) received from the mobile device  102  in the aforesaid digitally-signed message may be verified. If all of these checks succeed, the central server  104  issues a location proof for the mobile device  102  (pfD) that is returned to the anchor device  107  via TLS, see step  407 , and subsequently forwarded by the anchor device  407  to the mobile device  102  over NFC. 
     As would be appreciated by persons of ordinary skill in the art, the near-field nature of NFC ensures that the mobile device  102  is co-resident with the anchor device  107  when constructing its proof of authorization. To mitigate the threat of attacks in which multiple parties collude to produce a location proof for an off-site attacker, the anchor device  107  enforces tight timing constraints on the first message exchange in  FIG. 4 , see step  404 . Forwarding the nonce n to a colluding party via WIFI® or BLE and waiting for a response containing a signature would violate these timing constraints, causing the anchor device  107  to halt the protocol upon detecting unreasonable delays. Furthermore, the signatures of the client device  102  and the anchor device  107  on the third message of the protocol allow the central server  104  to ensure that the client device  102  and the anchor device  107  are actively cooperating in the construction of this proof. Specifically, the second message (which is signed by the client device  102 ) is embedded in the third message (which is signed by the anchor device  107 ), linking these messages to a single execution of the protocol. Finally, the cryptographic codes in the scan dataset, the anchor device  107  nonce n, and the timestamp on pfA allow for a check on the freshness of the process itself, preventing replay-style attacks. 
     In one or more embodiments, optionally, location proofs created with the assistance of the anchor device  107 , can be subjected to continuous monitoring in one of two ways. First, location-enabled applications running on the client device  102  or in other cloud services can register callbacks (via TLS) with the central server  104  to be notified when the mobile device  102  diverges from the location specified in its high-assurance proof, pfD. 
     Second, the anchor device  107  itself can play an active role in monitoring the location of nearby mobile devices  102 .  FIG. 5  illustrates an exemplary control flow  500  for (optional) BLE proximity checking with client device  102 . As shown in  FIG. 5 , BLE channel can be used to poll mobile devices  102  using a low-power signal to ensure that they remain within close proximity to the anchor device  107  (of which the hardware is controlled, trusted, and specifically configured). To ensure specific transmit power, a separate daughter BLE board could be used with firmware and/or physical antenna limitations to transmit at a low power (e.g., −20 dBm, with a receiving distance of approximately 1 meter would be limited to −115 dBm signal). At a configurable time interval, the anchor device  107  will use BLE to send a message identifying a particular device and providing it with a random challenge, see step  501  in  FIG. 5 . The mobile device  102  will then respond via BLE with a digital signature over that challenge, acknowledging that it was within close enough proximity to receive the challenge, see step  502 . Failure to respond to these challenges will trigger the anchor device  107  to contact the central server  104  to revoke the non-answering mobile device&#39;s  102  high assurance location proof. Similarly, if the accelerometer attached to the anchor device  107  detects that the anchor device  107  is being moved, it can be configured to revoke all high-assurance location proofs that were issued since it was anchored. 
     In one or more embodiments, a digitally-signed response  502  to the random challenge issued by the anchor device  107  ensures that some mobile device  102  was close enough to the anchor device  107  to hear the range-limited BLE transmission. Similar to the NFC protocol described above, restrictions on round-trip time for receiving this response mitigate the chance that a rogue mobile device  102  could forward the challenge to an out-of-range party to generate the signature. 
     In one or more embodiments, the high-assurance proofs of location may be further assisted using periodic or event-based triggers. In situations where environmental monitoring is not enough, applications  111  can request that user devices  102  refresh their high-assurance location proofs explicitly in either a periodic or event-driven manner. When an application  111  determines that a proof needs to be refreshed, it can request a new high-assurance proof from the location services module  103  of the mobile device  102 . This will raise an alert on the mobile device  102 , asking the user to engage the anchor device  107  in the protocol described in  FIG. 4 . In one or more embodiments, successful completion of this protocol will produce an updated high-assurance location proof, which will be returned to the location services  103  on the mobile device  102  and made available for consumption by the requesting application  111 . 
     Exemplary Use Cases and Applications 
     The description below provides several examples of how the described system  100  would be used by end-users in support of specific scenarios of uses. Each of the scenarios described begins with the anchoring of the anchor device  107  to a physical location, which is performed as follows. Specifically, to bind the anchor device  107  to a physical location, the user simply places the anchor device  107  on a flat surface and presses an anchor button on the anchor device  107 . First, the device determines its physical location as described above. In one embodiment, a small LED readout on the side of the anchor device  107  will subsequently display the location determined by the localization service  108 . To accept this location, the user presses the anchor button again, thereby locking the anchor device  107  to this physical location. At this point, the anchor device  107  is ready to participate in the construction of high-assurance proofs of location. 
     Scenario 1: Initial Localization Only. Many times, it may be the case that a high-assurance location proof is only requested at the start of a location-aware computing session (e.g., to enable access to sensitive resources), and lower-assurance proofs of location can be used for the purpose of continuous location tracking, revoking access if the device is found to drift from the location of the high-assurance proof. In this situation, it may be the case that administrative personnel bring in the anchor device  107  to start a work session, the device is anchored, and users leverage the device to bootstrap high-assurance location proofs. At this point, the administrative personnel can leave with the anchor device  107 , and users can continue their work until they leave the location. 
     Scenario 2: Ongoing Monitoring. The anchor device  107  can also play a more active role in the monitoring of user location after the initial high-assurance proof is created by closely monitoring its environment. Should any device move more than a few meters from the anchor device  107 , their high-assurance proof can be revoked by a cooperative action taken by the anchor device  107  and the central server  104 . Further, if the anchor device  107 , itself, determines that it is being moved, it can revoke all of the high-assurance proofs that it has helped create since the time that it was last anchored. 
     Scenario 3: Periodic or Event-based Triggers. There may be times at which an application requires the user to refresh their high-assurance location proof by placing their mobile device  102  on the anchor device  107 , and re-running the localization protocol. In various embodiments, this can be enabled via coordination between applications  111  running on the mobile device  102  and the anchor device  107 , through a cloud services API, and these triggers may be set periodically (e.g., once per hour) or in an event-driven manner (e.g., upon sensitive resource request). 
     Scenario 4: Digital Notary. The central server  104 , and by extension the anchor device  107 , provides a mechanism though which trusted location- and time-stamps can be created as described above. To this end, in various embodiments, the anchor device  107  can be used to coordinate the creation of bindings between multiple users&#39; mobile devices  102 , a physical location, a time, and some item of content, such as a document. This, effectively, can provide a high-assurance digital notary that can be used by a variety of applications. 
     Computing Platforms 
       FIG. 6  illustrates an exemplary embodiment of a computerized mobile system  600  that could be used as the mobile client device  102  in connection with the localization system  100  illustrated in  FIG. 1 . In one or more embodiments, the computerized mobile system  600  may be implemented within a form factor of a mobile computing device, such as a smartphone, a personal digital assistant (PDA), a tablet computer, or a smart watch, all of which are widely available commercially and are well known to persons of skill in the art. 
     The computerized system  600  may include a data bus  604  or other interconnect or communication mechanism for communicating information across and among various hardware components of the mobile computerized system  600 , and a central processing unit (CPU or simply processor)  601  coupled with the data bus  604  for processing information and performing other computational and control tasks. Computerized system  600  also includes a memory  612 , such as a random access memory (RAM) or other dynamic storage device, coupled to the data bus  604  for storing various information as well as instructions to be executed by the processor  601 . The memory  612  may also include persistent storage devices, such as a magnetic disk, optical disk, solid-state flash memory device or other non-volatile solid-state storage devices. 
     In one or more embodiments, the memory  612  may also be used for storing temporary variables or other intermediate information during execution of instructions by the processor  601 . Optionally, computerized system  600  may further include a read only memory (ROM or EPROM)  602  or other static storage device coupled to the data bus  604  for storing static information and instructions for the processor  601 , such as firmware necessary for the operation of the computerized system  600 , basic input-output system (BIOS), as well as various configuration parameters of the computerized system  600 . 
     In one or more embodiments, the computerized system  600  may incorporate a display device  609 , which may be also coupled to the data bus  604 , for displaying various information to a user of the computerized system  600 . In an alternative embodiment, the display device  609  may be associated with a graphics controller and/or graphics processor (not shown). The display device  609  may be implemented as a liquid crystal display (LCD), manufactured, for example, using a thin-film transistor (TFT) technology or an organic light emitting diode (OLED) technology, both of which are well known to persons of ordinary skill in the art. In various embodiments, the display device  609  may be incorporated into the same general enclosure with the remaining components of the computerized system  600 . In an alternative embodiment, the display device  609  may be positioned outside of such enclosure. 
     In one or more embodiments, the computerized system  600  may further incorporate an near field communication (NFC) interface  625  connected to the data bus  604  and configured to communicate with one or more NFC devices in the building as described above. 
     In one or more embodiments, the computerized system  600  may incorporate one or more input devices, such as a touchscreen interface  610  for receiving tactile commands, a camera  611  for acquiring still images and video of various objects, such as user&#39;s faces or room surroundings, as well as a keyboard  606 , which all may be coupled to the aforesaid data bus  604  for communicating information, including, without limitation, images and video, as well as user command selections to the processor  601 . In an alternative embodiment, input devices may include a system for tracking eye movements of the user (not shown), which may be used to indicate to the computerized system  600  the command selection by the user. 
     In one or more embodiments, the computerized system  600  may additionally include a location signal receiver  603  configured to perform scan for beacons  101  and supply scan data described above to the processor  601  via the data bus  604 . 
     In one or more embodiments, the computerized system  600  may additionally include a communication interface, such as a network interface  605  coupled to the data bus  604 . The network interface  605  may be configured to establish a connection between the computerized system  600  and the Internet  624  using at least one of WIFI interface  607  and the cellular network (GSM or CDMA) adaptor  608 . The network interface  605  may be configured to provide a two-way data communication between the computerized system  600  and the Internet  624 . The WIFI interface  607  may operate in compliance with 802.11a, 802.11b, 802.11g and/or 802.11n protocols as well as BLUETOOTH® protocol well known to persons of ordinary skill in the art. In an exemplary implementation, the WIFI interface  607  and the cellular network (GSM or CDMA) adaptor  608  send and receive electrical or electromagnetic signals that carry digital data streams representing various types of information. For example, the aforesaid networking components may be used to establish a network data connection between the computerized system  600  and other components of the localization system  100 , such as the central server  104  and third party services/applications  108 . 
     In one or more embodiments, the Internet  624  typically provides data communication through one or more sub-networks to other network resources. Thus, the computerized system  600  is capable of accessing a variety of network resources located anywhere on the Internet  624 , such as web servers, other content servers as well as other network data storage resources. In one or more embodiments, the computerized system  600  is configured send and receive messages, media and other data, including application program code, through a variety of network(s) including Internet  624  by means of the network interface  605 . In the Internet example, when the computerized system  600  acts as a network client, it may request code or data for an application program executing on the computerized system  600 . Similarly, it may send various data or computer code to other network resources. 
     In one or more embodiments, the computerized system  600  uses the network interface  605  to send request(s), via the Internet  624 , such as HTTP requests, to the central server  104  and receive various information, including, without limitation, the aforesaid location information and the timestamp, therefrom. 
     In one or more embodiments, the functionality described herein is implemented by computerized system  600  in response to processor  601  executing one or more sequences of one or more instructions contained in the memory  612 . Such instructions may be read into the memory  612  from another computer-readable medium. Execution of the sequences of instructions contained in the memory  612  causes the processor  601  to perform the various process steps described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiments of the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software. 
     The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor  601  for execution. The computer-readable medium is just one example of a machine-readable medium, which may carry instructions for implementing any of the methods and/or techniques described herein. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. 
     Common forms of non-transitory computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punchcards, papertape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EPROM, a flash drive, a memory card, any other memory chip or cartridge, or any other medium from which a computer can read. Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor  601  for execution. For example, the instructions may initially be carried on a magnetic disk from a remote computer. Alternatively, a remote computer can load the instructions into its dynamic memory and send the instructions over the Internet  624 . Specifically, the computer instructions may be downloaded into the memory  612  of the computerized system  600  from the foresaid remote computer via the Internet  624  using a variety of network data communication protocols well known in the art. 
     In one or more embodiments, the memory  612  of the computerized system  600  may store any of the following software programs, applications or modules: 
     1. Operating system (OS)  613 , which may be a mobile operating system for implementing basic system services and managing various hardware components of the computerized system  600 . Exemplary embodiments of the operating system  613  are well known to persons of skill in the art, and may include any now known or later developed mobile operating systems. 
     2. Mobile applications  614  may include, for example, a set of software applications executed by the processor  601  of the computerized system  600 , which cause the computerized mobile system  600  to perform certain predetermined functions, such as receive the beacon signals as described above. In one or more embodiments, the mobile applications  614  may include, for example, the location services  103 , anchor services  615  (which could be either anchor services  109  or  106 ), environmental monitor  110  as well as one or more client applications  111 , see  FIG. 1 . 
     3. Data storage  616  may be used, for example, for storing the bacon scan data  617  as well as location data  618  of the computerized mobile system  600 . 
       FIG. 7  illustrates an exemplary embodiment of a computerized server system  700  which could be used, for example, as the central server  104  of the localization system  100  shown in  FIG. 1 . It should be noted that other components of the localization system  100 , including, without limitation, the cloud beacon agent  105 , may be also deployed based on the computerized server system  700 . 
     In one or more embodiments, the computerized server system  700  may incorporate a data bus  704 , which may be substantially similar and may perform substantially similar functions as the data bus  704  of the computerized system  600  illustrated in  FIG. 9 . In various embodiments, the data bus  704  may use the same or different interconnect and/or communication protocol as the data bus  604 . The one or more processors (CPUs)  701 , the network adaptor  705 , the EPROM/Firmware storage  702 , the display device  709  and the keyboard  706  of the computerized server system  700  may be likewise substantially similar to the respective processor  601 , the network interface  605 , the EPROM/Firmware storage  602 , the display device  609  and the keyboard  606  of the computerized system  600 , except that the former components are deployed in a server platform configuration. In various implementations, the one or more processor  701  may have substantially increased processing power as compared with the processor  601 . 
     In addition to the input device  706  (keyboard), the computerized server system  700  may additionally include a cursor control device  710 , such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor  701  and for controlling cursor movement on the display device  709 . This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. 
     The LAN/ISDN adaptor  707  of the computerized server system  700  may be implemented, for example, using an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line, which is interfaced with the Internet  624  using Internet service provider&#39;s hardware (not shown). As another example, the LAN/ISDN adaptor  707  may be a local area network interface card (LAN NIC) to provide a data communication connection to a compatible LAN and the Internet  624 . To store various media files, the computerized server system  700  may be provided with document storage  708 , for storing various content to be displayed to the user by means of a storage controller  703 . The camera  711  may be used to acquire images and/or video of various objects. 
     In one or more embodiments, the memory  712  of the computerized server system  700  may store any of the following software programs, applications, modules and/or data: 
     1. A server operating system (OS)  713 , which may be an operating system for implementing basic system services and managing various hardware components of the computerized server system  700 . Exemplary embodiments of the server operating system  713  are all well known to persons of skill in the art, and may include any now known or later developed operating systems. 
     2. A network communication module  714  may incorporate, for example, one or more network protocol stacks which are used to establish a networking connection between the computerized server system  700  and the various network entities of the Internet  624 , such as the computerized mobile system  600 , using the network adaptor  705  working in conjunction with the LAN/ISDN adaptor  707 . 
     3. Server applications  715  may include, for example, a set of software applications executed by one or more processors  701  of the computerized server system  700 , which cause the computerized server system  700  to perform certain predetermined functions or tasks. In one or more embodiments, the server applications  715  may include the location classification engine  109 . 
     4. Data storage  719  may be used, for example, for storing the location data  720 , described above, which may be stored in a form of database tables. 
     Finally, it should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein. The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. For example, the described software may be implemented in a wide variety of programming or scripting languages, such as Assembler, C/C++, Objective-C, perl, shell, PHP, Java, as well as any now known or later developed programming or scripting language. 
     Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination in various localization systems and methods. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.