Patent Publication Number: US-2022225107-A1

Title: Spatial web of trust key initialization method for sensor platform array using directed close-field communication

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority to U.S. Provisional Application No. 63/136,012, filed on Jan. 11, 2021, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Data encryption is the process of converting data into a scrambled and unintelligible form, commonly referred to in the art as cipher data. Data of various types may be encrypted for storage as well as transmission, with an overarching goal of data encryption ultimately being one of improved security from theft or alteration. Encryption algorithms typically incorporate the use of unique passwords or keys that a recipient of the encrypted data inputs to automatically decrypt the stored or transmitted encrypted data. Common types of encryption include Data Encryption Standard (DES), Triple DES, Advanced Encryption Standard (AES), Rivest-Shamir-Adleman (RSA), and TwoFish, among others. 
     In the realm of cryptography, a “web of trust” is often used to establish secure networked communication between multiple compatible devices. In general terms, a web of trust is a decentralized trust model often used as an alternative to centralized trust models, such as Public Key Infrastructure (PKI) or another centralized cryptosystem. Unlike PKI, which relies on the use of a highly hierarchical certificate authority, the more informal web of trust provides a decentralized mechanism for determining the validity of public keys. Users of such an approach are thus able to post new identifying keys to other trusted users forming the “web” of the web of trust, with the keys of different users automatically validated during a pairing process when constructing the web. 
     SUMMARY 
     The present disclosure relates to methods and systems for initializing a spatial web of trust for a sensor platform array. The sensor platform array may be constructed from an application-suitable number of constituent mobile or stationary sensors in different embodiments, such as but not limited to an airborne, seaborne, or terrestrial drone swarm or a fixed array of sensor platforms. As used herein, the term “sensor” broadly encompasses any device capable of detecting or otherwise receiving inputs and responding thereto in a controlled manner, including autonomous control scenarios as described herein. Representative embodiments of sensors mountable on a given sensor platform include lidar or radar sensors, electrooptical, infrared, ultraviolet, or multi-spectral cameras, global positioning system (GPS) receivers, inertial sensors, temperature, moisture, and/or windspeed sensors, microphones, intelligent lighting devices, transceivers, light-emitting devices, and the like, depending on the particular application. The sensor array may be constructed of like or different types of sensors, again depending on the application. 
     An embodiment of the present method includes arranging the sensor platform array in multiple groups of sensor platforms (“sensor groups”) within a restricted workspace. In this manner, adjacent sensor platform pairs are formed from corresponding sensor platforms of each respective one of the sensor groups. This occurs within a predetermined or non-predetermined close-field range as described in detail below, with the close-field range typically being less than 1 meter (m) to about 50 m depending on the application and size of the sensor platforms in use. The method in this embodiment includes exchanging sensor-specific identification keys between the adjacent corresponding sensor platforms, with such a key exchange occurring using respective signal transceivers of the respective sensor platforms. 
     The method further includes progressively repositioning the multiple sensor groups to form unique adjacent sensor platform pairs within the predetermined or non-predetermined close-field range. In response such repositioning, the keys are progressively exchanged until each sensor platform of the array has exchanged a respective one of the keys with every other sensor platform in the array, thereby initializing the spatial web of trust. 
     Each sensor platform may be mounted on a respective mobile drone in some configurations, with the sensor platform array in such an embodiment that it constitutes a drone swarm. A drone swarm in a disclosed exemplary embodiment is an aerial drone swarm constructed of unmanned aerial vehicles (UAVs), although land-based and surface or subsurface water-based drone swarms may also be contemplated within the scope of the present disclosure. 
     The restricted workspace in the UAV swarm embodiment forms a three-dimensional airspace, such as a 10 meter (m)×10 m×10 m, or 20 m×20 m×20 m, or 100 m×100 m×100 m restricted three-dimensional airspace in non-limiting exemplary setups. Arranging the array or the sensor groups thereof may include, in such an embodiment, autonomously or semi-autonomously controlling flight operations of the UAV swarm within the three-dimensional airspace. Controlling the flight operation of the UAV swarm includes transmitting flight control instructions to the UAV swarm from a terrestrial base station over a ground-to-air communications link. 
     Controlling flight operations of the UAV swarm may itself includes executing a set of non-local or local instructions using a respective processor or central processing unit of each of a plurality of UAVs, which would enable autonomous control of the flight operations of the collective UAV swarm. Alternatively, controlling flight operations could entail directing the flight operations from a terrestrial or airborne base station in real-time, e.g., using a secure/encrypted or unencrypted radio and/or optical communications link. 
     Arranging the sensor groups of the array within the restricted workspace may include arranging sensor platforms of each of the multiple sensor groups around a respective annular perimeter, and thus in separate quasi-circular formations. In such an approach, arranging the multiple sensor groups includes counter-rotating the sensor groups around the respective perimeters to sequentially form the unique adjacent sensor platform pairs, as well as subdividing and counter-rotating each of the multiple sensor groups in response to detection of a duplicate adjacent sensor platform pair, i.e., a pair of the sensor platforms for which the sensor-specific identification keys were previously exchanged, and subdividing and counter-rotating each of the multiple sensor groups in response to detecting the duplicate adjacent sensor platform pair. 
     Arranging the sensor platforms around the respective perimeters of the quasi-circular formations may include, according to an alternative approach, arranging the sensor platforms on different physical turntables, e.g., rotary plates or another suitable support structure. Positioning the sensor groups in this particular embodiment thus includes counter-rotating the different turntables, for example using a corresponding drive torque from a respective electric motor. The method in such an embodiment includes detecting a completed exchange of the above-noted keys between the respective sensor platforms of the adjacent pairs, and then counter-rotating the turntables automatically via an electronic control unit using the drive torques in response to the completed exchange. 
     Also disclosed herein is a system for initializing a spatial web of trust for an autonomous unmanned aerial vehicle (UAV) swarm. The system includes a base station and the UAV swarm, with the UAV swarm being in communication with the base station over a communications link. The communications link is at least one of an air-to-air communications link or a ground-to-air communications link. Each respective UAV of the UAV swarm includes a central processing unit (CPU), a sensor suite, and memory on which is recorded instructions. Execution of the instructions by the CPU, in response to an initiation signal from the base station, causes an autonomous arranging of multiple autonomous UAV groups of autonomous UAVs of the UAV swarm within a restricted airspace. An adjacent UAV pair is thereby formed from a corresponding UAV of each respective one of the multiple UAV/sensor groups within a predetermined or non-predetermined close-field range. 
     In this embodiment, execution of the instructions causes an exchange of UAV-specific identification keys between respective UAVs of the adjacent UAV pairs using respective transceivers of the respective UAVs, the transceivers being at least one of radio transceivers or optical transceivers, along with progressive repositioning of the UAV groups, via control of a flight operation of the UAV swarm, which may occur autonomously, using the communications link with the base station, or both. Doing this forms unique adjacent UAV pairs within the predetermined or non-predetermined close-field range. In response to the repositioning, the same instructions cause progressive exchanging of the UAV-specific identification keys. This continues until each UAV of the UAV swarm has successfully exchanged a respective one of the UAV-specific identification keys with every other UAV in the UAV swarm, thereby initializing the spatial web of trust. 
     The above summary is not intended to represent every possible embodiment or every aspect of the present disclosure. Rather, the foregoing summary is intended to exemplify some of the novel aspects and features disclosed herein. The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of representative embodiments and modes for carrying out the present disclosure when taken in connection with the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a representative sensor platform array in the exemplary form an unmanned aerial vehicle swarm, the individual sensor platforms of which form a spatial web of trust that is initialized in accordance with the method described herein. 
         FIG. 2  is a flow chart describing an exemplary embodiment for implementing the present method. 
         FIGS. 3, 4, and 5  schematically depict a progressive exchange of sensor-specific identification keys in accordance with the present disclosure. 
         FIG. 6  depicts an alternative mechanical turntable-based embodiment for use with the method of  FIG. 2 . 
     
    
    
     The present disclosure is susceptible to modifications and alternative forms, with representative embodiments shown by way of example in the drawings and described in detail below. Inventive aspects of this disclosure are not limited to the disclosed embodiments. Rather, the present disclosure is intended to cover alternatives falling within the scope of the disclosure as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples, and that other embodiments can take various and alternative forms. The Figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure. 
     Certain terminology may be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “above” and “below” refer to directions in the drawings to which reference is made. Terms such as “front,” “back,” “fore,” “aft,” “left,” “right,” “rear,” and “side” describe the orientation and/or location of portions of the components or elements within a consistent but arbitrary frame of reference, which is made clear by reference to the text and the associated drawings describing the components or elements under discussion. Moreover, terms such as “first,” “second,” “third,” and so on may be used to describe separate components. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. 
     Referring to the drawings, wherein like reference numbers refer to the same or like components in the several Figures, a representative sensor platform array  10  is shown schematically in  FIG. 1 , with the sensor platform array  10  having a plurality of sensor platforms  12 . Collectively, the sensor platform array  10  acts as a spatial web of trust within the scope of the present disclosure, with the individual sensor platforms  12  operating autonomously in the performance of a particular mission task. 
     As used herein and in the art, particularly with respect to networked cryptography, a web of trust is often used as a decentralized trust model in lieu of a more centralized public key infrastructure, better known as PKI. In general, each member of a web of trust must first be made aware of every other member&#39;s corresponding identification key. Communication between any two members in a given sender-recipient pairing thus involves encryption by the sensor of the particular data with the recipient&#39;s unique identification key. The recipient alone is thus configured to decrypt the transmitted encrypted data. For communication to occur reliably and seamlessly in a web of trust framework, therefore, each member of the web of trust must be made aware of the corresponding identification keys of every other member. To this end, the present disclosure provides directed-field solutions to the challenge of populating the web of trust via the orchestrated exchange of such identification keys. 
     While the individual sensor platforms  12  are depicted in  FIG. 1  as unmanned aerial vehicles (UAVs) or other pilotless aerial drones, and thus the sensor platform array  10  is embodied as a representative drone/UAV swarm as set forth herein, those skilled in the art will appreciate that other types of sensor platform arrays  10  and constituent sensor platforms  12  may be envisioned within the scope of the present disclosure. For instance, the individual sensor platforms  12  need not be mobile, but rather could be configured as any number of stationary platforms for use with sensors  40  such as cameras, microphones, thermal sensors, intelligent lighting devices, weather sensors, transponders, lidar sensors, radar sensors, and the like, depending on the particular application. 
     Likewise, various other mobile applications may be readily envisioned in which the sensor platforms  12  are deployed on tracked or wheeled terrestrial surface vehicles, propeller or jet-powered surface or subsurface watercraft, or in operating environments other than the representative airborne application of  FIG. 1 . Solely for illustrative consistency, however, the sensor platform array  10  and sensor platforms  12  will be described hereinafter as a UAV swarm  10  and UAVs  12 , respectively, without limitation. 
     As appreciated in the art, missions ranging in scope from package delivery to the monitoring of traffic, search and rescue operations, atmospheric weather patterns, or difficult to access locations and/or remote infrastructure entails a broad range of data collection capabilities. Reliable collection, distribution, and consumption of collected data thus requires carefully coordinated data collection from multiple points-of-origin over an associated communication network. In some cases, backhaul capabilities are used to distribute collected data to a remotely located end user, often using satellite or ground-based relays to facilitate the backhaul capability. Such backhaul capabilities may be lost or rendered temporarily unavailable due to a host of possibly manmade and natural factors. The use of a UAV swarm such as the depicted UAV swarm  10  of  FIG. 1  may be used to advantage in such backhaul-deprived environments, as well as in operating environments in which such capabilities remain intact. 
     In the non-limiting aerial scenario illustrated in  FIG. 1 , the UAV swarm  10  is deployed from an aircraft  16 , such as from a payload bay door (not shown). For instance, the aircraft  16  could fly to a predetermined or non-predetermined rendezvous location at a predetermined or non-predetermined mission-suitable altitude. Once arriving on station, the aircraft  16  could deploy the UAV swarm  10 , at which point each UAV  12  autonomously engages in a collectively-coordinated mission. In such a use scenario, the UAVs  12  could each collect sensor-specific data and relay the collected data back to the orbiting aircraft  16 , or each UAV  12  could perform an individually assigned mission task in close cooperation with the other UAVs  12  in the collective UAV swarm  10 . 
     To function as a cohesive unit in such a use scenario, the UAV swarm  10  is first constituted as an exclusive spatial web of trust in accordance with the present disclosure. Accordingly, each UAV  12  is pre-populated with unique sensor-specific identification keys of each of the other member UAVs  12  in the UAV swarm  10 . The present approach offers a particular solution to the problem of accurate and efficient key initialization in the context of establishing the web of trust. The present method  50 , an embodiment of which is described below with reference to  FIG. 2 , is useful not only within the context of the exemplary UAV swarm  10  shown in  FIG. 1 , but also for mobile or stationary sensor platform arrays of other types, as noted above. 
     In the non-limiting embodiment of  FIG. 1 , the UAV swarm  10  is shown positioned within a restricted workspace  18 . As used herein, the term “restricted workspace” may entail a three-dimensional application-suitable airspace in which the UAVs  12  are isolated or set a sufficient distance apart from other signal-emitting devices, and thus are protected from electromagnetic interference or signal interception during the course of executing the present method  50 . The size of the restricted workspace  18  varies with that of the individual UAVs  12 , with the depicted size not necessarily shown to scale. 
     By way of example and not limitation, the restricted workspace  18  for the illustrated airborne-deployed UAV swarm  10  in which each member UAV  12  has a wingspan of about 1 meter (m) may be on the order of 10 m×10 m×10 m to 20 m×20 m×20 m. The actual size of the restricted workspace  18  is highly scalable to other sizes and types of UAVs  12 , e.g., fixed-wing drones or gliders, or rotary configurations other than the non-limiting quadcopter embodiment shown in  FIG. 1 . An altitude of the restricted workspace  18  likewise depends on the mission/application, with variations being possible depending on whether the UAVs  12  are deployed at altitude in proximity to the restricted workspace  18  from the aircraft  16  while the aircraft  16  is in flight, or instead launched from a surface  20 , e.g., a ground surface as depicted in  FIG. 1 , with water surface-based launches likewise possible within the scope of the disclosure. 
     An optional base station  22  may be used to transmit mission or flight operations instructions  24  over an encrypted or unencrypted communications link via a directional or omni-directional antenna  26  to one or more of the UAVs  12  when executing the present method  50 . Such signal transmission is represented by double-headed arrow AA in  FIG. 1 . The base station  22  could be a stationary or mobile facility located on the ground surface  20 , with such a base station  22  referred to as a terrestrial base station  22  in such an embodiment, or the base station  22  could be an airborne base station  22  present aboard/integrated with the aircraft  16  in different embodiments. Fully-autonomous embodiments may also be envisioned in which each UAV  12  is programmed in software and equipped in hardware to execute corresponding instructions for implementing the present method  50 . That is, the UAVs  12  while in flight could individually and cooperatively execute the method  50  so as to move in a well-choreographed manner within the restricted workspace  18 , as set forth in detail below with reference to  FIGS. 3-5 , when exchanging sensor-specific identification keys in the course of initializing the above-noted web of trust. 
     To that end, each UAV  12  of the collective UAV swarm  10  shown schematically in  FIG. 1  may include a corresponding local controller  30  for a representative UAV pair  12 P, i.e., two adjacent aerial UAVs  12  within the above-noted close-field range. Two-way wireless authentication between the local controllers  30  of the UAV pair  12 P is represented by double-headed arrow BB. Each local controller  30  is equipped with application-specific amounts of volatile and non-volatile memory (MEM)  32  and a central processing unit (CPU)  34 , as well as other associated hardware and software. Exemplary hardware includes input/output (I/O) circuitry  36  and an electro-optical signal transceiver (Tx/Rx)  38 , as well as a digital clock or timer, signal buffer circuitry, etc., any or all of which may be embodied as an Application Specific Integrated Circuit (ASIC) or a System-on-a-Chip (SoC) to provide the programmed functionality. Each local controller  30  includes an onboard sensor suite 40, e.g., a discrete sensor or a multitude of sensors, with various embodiments of the sensors  40  described above and understood by those skill in the art. As part of the method  50 , each local controller  30  is in close-field communication with a counterpart UAV  12  to form the UAV pair  12 P when a pair of the UAVs  12  are positioned within a close-field range of each other. 
     Turning now to  FIG. 2 , a representative embodiment is shown for implementing the present method  50  when initializing a spatial web of trust with a suitable sensor array. In keeping with the non-limiting UAV swarm  10  of  FIG. 1 , the method  50  assumes availability of a suitably equipped population of UAVs  12 , each of which is equipped with flight control logic and avionics (not shown), the sensor(s)  40  of  FIG. 1 , and other requisite hardware for performing an assigned mission task. Additionally, the memory  32  of  FIG. 1  is populated with instructions for executing the method  50 , and in particular for enabling the UAV  12  to position itself in accordance with a predetermined or non-predetermined flight plan when maneuvering in free space within the restricted workspace  18 . 
     Commencing with logic block B 52 , the method  50  in the depicted embodiment entails staging or purposefully arranging the UAVs  12  within the restricted workspace  18  shown in  FIG. 1 . In a non-limiting exemplary application, for instance, logic block B 52  includes deploying the UAV swarm  10  from the aircraft  16 , launching the UAVs  12  from the ground surface  20 , or otherwise moving the UAVs  12  into the restricted workspace  18 . As described below and as shown as an optional restricted workspace  118  in  FIG. 6 , the restricted workspace need not be an airborne workspace within the scope of the disclosure, i.e., mobile embodiments of the UAVs  12  need not be flown when performing logic block B 52 . The method  50  proceeds to logic block B 54  when the UAVs  12  have been arranged in the restricted workspace  18 . 
     Logic block B 54  includes dividing the UAVs  12  into multiple UAV groups G 1  and G 2  (see  FIG. 3 ), with the UAV groups being one possible type of sensor group within the scope of the disclosure. Such a division is performed regardless of whether the total number of UAVs  12  in the UAV swarm  10  is odd or even. For an odd number, however, the groups G 1  and G 2  will have a different relative number of UAVs  12 , e.g., five and four in a representative nine-UAV population. For simplicity, an even number of aerial UAVs  12  is shown in  FIGS. 3-5  as eight UAVs  12 , respectively labeled (1), (2), . . . , (8) for clarity. 
     Logic block B 54  of  FIG. 2  may entail arranging the UAV swarm  10  or other sensor platform array in the multiple sensor groups, e.g., UAV groups G 1  and G 2  in a simplified embodiment, within the restricted workspace  18  or  118 , such that multiple adjacent sensor UAV pairs  12 P are formed within a predetermined or non-predetermined close-field range from adjacent corresponding UAVs  12  of each respective one of the multiple UAV groups G 1  and G 2 . In a particular embodiment, positioning the UAV groups G 1  and G 2  of the UAV swarm  10  within the restricted workspace  18  of  FIG. 1  includes arranging UAVs  12  of each of the UAV groups G 1  and G 2  around a respective perimeter of separate quasi-circular formations, as best shown in  FIGS. 3-5 . 
     Additionally, execution of block B 54  includes, in some embodiments, controlling flight operations of the UAV swarm  10  within the restricted workspace  18 , in this instance a three-dimensional airspace at an application-suitable altitude above the ground surface  20  shown in  FIG. 1 . Such positioning occurs within a directed close-field range. As used herein, the term “close-field” refers to an application-specific linear distance in which the transceivers  38  of the UAVs  12  are able to directionally or omni-directionally exchange their respective unique identifying keys in encrypted or unencrypted form when the UAVs  12  are moved or flown into a close-field proximity of one another. 
     The actual distance of such close-field proximity will be proportionate to the size of the UAVs  12  and the particular frequencies and transmission ranges over which the UAVs  12  communicate. Near-field communication (NFC) ranges of about 35 cm or less could conceivably be used in some embodiments, such as those shown in  FIG. 6  in which flight operations are not required. NFC ranges may be particularly useful when using miniaturized UAVs  12  or other diminutive stationary or mobile sensors. Other embodiments may be conceived in which the close-field range is greater than typical NFC ranges, e.g., BLUETOOTH. For example, the close-field range contemplated herein may be on the order of about 1-10 m or 1-50 m in non-limiting exemplary embodiments, or another flight-safe standoff distance that is close enough for performing the method  50  without adversely affecting flight dynamics and safety, while ensuring signal transmission security and integrity. 
     The application-specific close-range communication protocol used in the course of executing the method  50  may be used in conjunction with different transmission hardware constructions. Directed communications are used to ensure receipt of the exchanged encrypted identification keys only by the UAVs  12  forming a given UAV pair  12 P. Thus, the transceivers  38  of  FIG. 1  may be provided with an application-suitable antenna geometry, and tuned to provide the required secure transmission range. Techniques such as beam forming may also be used to this end, albeit at the expense of added complexity. 
     As shown in  FIG. 3 , the UAV swarm  10  may include eight UAVs  12 , nominally labeled (1), (2), (3), (4), (5), (6), (7), and (8) for clarity. Thus, block B 54  of  FIG. 2  could entail dividing the UAV swarm  10  into two groups of four UAVs  12  in this illustrative embodiment, and then situating each UAV group G 1  and G 2  adjacent to the other, such that each UAV  12  of group G 1  is positioned immediately adjacent to another UAV  12  from group G 2 . Such positioning is shown schematically in  FIG. 3  with UAVs  12  numbered (1), (2), (3), and (4) positioned in one quasi-circular arrangement, and with UAVs  12  numbered (5), (6), (7), and (8) being similarly positioned. UAV groups G 1 =(1, 2, 3, 4) and G 2 =(5, 6, 7, 8) are thus roughly concentrically arranged as shown. Such positioning thus ensures an initial pairing arrangement of the UAVs  12  in pairs (4, 8), (3, 7), (2, 6), and (5, 1). Alternatively, groups G 1  and G 2  may be of any size and are not required to be of equal or close to equal sizes, and are not required to have an equitable initial pairing arrangement. Alternatively, more groups than the illustrated groups G 1  and G 2  may be defined and positioned adjacent to each other in similar manners. 
     Attendant actions needed for dividing the UAVs  12  into groups G 1  and G 2  of  FIG. 3  will depend on the construction of the UAVs  12  and the size and location of the restricted workspace  18 , as will be appreciated by those skilled in the art. For example, in the non-limiting airborne application of  FIG. 1 , the UAVs  12  may fly autonomously to the designated restricted workspace  18 , or the UAVs  12  may be directed via an analogous air traffic controller, e.g., the base station  22  on the ground surface  20  or aboard the orbiting aircraft  16  of  FIG. 1 . 
     Alternatively as shown in  FIG. 6 , the UAVs  12  may be situated on turntables  42  and  142 , whether mechanical or quasi-mechanical. For instance, the turntables  42  and  142  may be configured as large moveable plates or platforms having respective rotational positions controlled by a corresponding electric motor (M 1 )  43  and (M 2 )  143 . That is, the UAVs  12 , rather than being flown as in  FIG. 1 , may instead be placed in the above-noted quasi-circular pattern around the perimeters of the turntables  42  and  142 . An electronic control unit (ECU)  44  having associated memory (M) and a processor (P), analogous to the memory  32  and CPU  34  of  FIG. 1 , may then execute instructions embodying the method  50  to control positioning and data exchange between the aerial UAVs  12 . For example, the ECU  44  may output torque commands (arrows T 1  and T 2 ) to the respective electric motors  43  and  143  in response to motor control signals (arrows CC M1  and CC M2 ) to cause a corresponding rotation of the turntables  42  and  142  within another restricted workspace  118 . Block B 54  of  FIG. 2  proceeds to block B 56  after the two UAV groups G 1  and G 2  of  FIG. 3  have been formed in an application-suitable manner. 
     Block B 56  of the method  50  shown in  FIG. 2  includes exchanging sensor-specific identification keys between respective UAVs  12  of adjacent UAV pairs  12 P. This action occurs using the transceivers  38  of the respective UAVs  12  (see  FIG. 2 ) and associated communications protocols. After an exchange of sensor-specific identification keys by the UAV pairs  12 P, e.g., UAV pairs (4, 8) and (2, 6) in the initial position of  FIG. 3 , the quasi-circular arrangements are counter-rotated. Such movement is represented in  FIG. 4  by arrows CW and CCW, with aerial UAVs or drones  12  labeled (5, 6, 7, 8) rotating counter-clockwise (arrow CCW) and UAVs/drones  12  labeled (1, 2, 3, 4) rotating clockwise (arrow CW) in the depicted embodiment. As appreciated, the relative direction of rotation is immaterial, provided that the two UAV groups G 1  and G 2  rotate in opposite directions. Counter-rotating the mechanical turntables  42  and  142  in the alternative  FIG. 6  embodiment could occur automatically via the ECU  44  in response to the successful exchange. 
     Block B 56  of  FIG. 2  proceeds to block B 58 , with blocks B 56  and B 58  of the method  50  continuing in a sequential iteration until it is determined at block B 58  that a duplicate UAV pair  12 P is attempting or will attempt to pair. As used herein, a duplicate UAV pair  12 P is a UAV pair  12 P having previously exchanged the above-noted UAV-specific identification keys. Thus, method  50  includes progressively repositioning the UAV groups G 1  and G 2  to form unique adjacent UAV pairs  12 P within the predetermined or non-predetermined close-field range noted above. 
     For example, the illustrated example of  FIG. 4  starts out with UAV pairs (1, 5), (2, 6), (3, 7), and (4, 8). The UAV groups G 1  and G 2  then counter-rotate once, as indicated by arrow C, to form new UAV pairs (1, 8), (2, 5), (3, 6), and (4, 7). Autonomous counter-rotation of the UAV groups G 1  and G 2  occurs around the respective perimeters of the above-noted quasi-circular arrangements in order to sequentially form the unique adjacent sensor platform pairs. 
     Following this control action, another counter-rotation (arrow D) occurs to form new UAV pairs (1, 7), (2, 8), (3, 5), and (4, 6). In the same manner, the next counter-rotation (arrow E) results in new UAV pairs (1, 6), (2, 7), (3, 8), and (4, 5). So far in the described counter-rotation sequence, the counter-rotations of arrows C, D, and E produce only new/previously unrecorded pairings. However, were another counter-rotation to be attempted, the resulting relative positions would be the same as the initial set, i.e., UAV pairs (1, 5), (2, 6), (3, 7), and (4, 8). The method  50  thus includes detecting, as a duplicate adjacent UAV pair  12 P at block B 58 , an adjacent sensor pair for which the sensor-specific identification keys were previously exchanged. The method  50  then proceeds to block B 60 . 
     Blocks B 60  and B 62  respectively include subdividing the UAV groups G 1  and G 2  into UAV sub-groups G 1 A, G 1 B and G 2 A, G 2 B, respectively, and thereafter repeating the above-described key exchange and counter-rotating of the new sub-groups. As a simplified example,  FIG. 5  commences with the ending spatial arrangement of  FIG. 4 , i.e., with UAV pairs (1, 6), (2, 7), (3, 8), and (4, 5). At block B 60 , since duplicate UAV pairs would be detected with the next counter-rotation, the method  50  subdivides UAV group G 1  and G 2 , i.e., UAVs/drones  12  labeled (1, 2, 3, 4) and (5, 6, 7, 8). 
     For example, subdividing the UAVs  12  (1, 2, 3, 4) results in two new subgroups, i.e., UAVs  12  labeled (1) and (2) forming sub-group G 1 A and UAVs  12  labeled (3) and (4) forming sub-group G 1 B, as indicated by arrow F. Likewise, subdividing UAVs  12  labeled (5, 6, 7, 8) results in two new sub-groups G 2 A and G 2 B, i.e., UAVs/drones  12  labeled as (5, 6) and UAVs/drones  12  labeled as (7, 8), with this subdivision indicated by arrow G. As shown, the result is new pairings of UAVs/drones (1, 4), (2, 3), (5, 8), and (6, 7). Another counter-rotation of each subgroup results in pairings (2, 4) and (1, 3), as indicated by arrow H, as well as pairings (6, 8), and (5, 7) as indicated by arrow I. The method  50  then proceeds to block B 64 . 
     At block B 64 , the method  50  includes determining whether the next counter-rotation would result in a duplicate UAV pair  12 P. This may entail detecting the duplicate UAV pair  12 P or other adjacent sensor platform pair in other embodiments, with the duplicate UAV pair  12 P/adjacent sensor platform pair being one for which the sensor-specific identification keys were previously exchanged. The method  50  repeats block B 62  when a duplicate UAV pair  12 P would not result. Otherwise, the method  50  proceeds to block B 66 . 
     Block B 66  entails exchanging unique identifying keys of the final UAV pairs  12 P, the identify of which corresponds to the UAVs  12  situated in the inner and outer quasi-circular arrangements. In the example of  FIG. 5 , for instance, as the radially innermost UAVs  12  are numbered (3) and (4) and the outermost UAVs  12  are numbered (1) and (2), block B 66  includes pairing the UAVs (3, 4) and (1, 2), as respectively indicated by arrow J and arrow K. The same process is performed for the inner grouping of UAVs  12 , i.e., (7, 8), and the outer grouping (5, 6) in order to pair the UAVs (7, 8) and (5, 6) and exchange the above-noted encrypted identification keys, as indicated by arrows L and M, respectively. Thus, in response the repositioning conducted in blocks B 56 -B 62 , the method  50  includes progressively exchanging the sensor-specific identification keys until each UAV  12  of the UAV swarm  10  has exchanged a respective sensor-specific identification key with every other UAV  12  in the UAV swarm  10 , thereby initializing the above-noted web of trust. 
     As will be appreciated by those skilled in the art in view of the foregoing disclosure, aspects of the present method  50  described above include controlling flight operations of the aerial drone or UAV swarm  10  of  FIG. 1  in real-time by executing a set of instructions embodying the method  50 . This occurs using a respective CPU  34  of each one of the UAVs  12 , with such hardware depicted schematically in  FIG. 2 . In this manner, the method  50  may include autonomously controlling a flight operation of the UAV swarm  10 , such that the UAV swarm  10  functions as a collective unit. 
     Controlling a flight operation of the UAV swarm  10  in any of the preceding logic blocks of method  50  may include directing the flight operation of the UAV swarm  10  from the base station  22  of  FIG. 1  in real-time, e.g., using a secure encrypted or unencrypted radio communication link or a secure optical communication link, with the need for encryption in a given instance being dependent upon the operating environment and application. Once the method  50  is complete, operational control of the UAV swarm  10  may be in accordance with other algorithms not described herein, possibly with in-the-loop direction from the aircraft  16 , the base station  22 , or both. 
     As will be appreciated, the UAV swarm  10  once initialized in accordance with the present method  50  may be used to autonomously perform a myriad of possible mission tasks. Beyond “trusted wingman” type missions in which the UAVs  12  of the UAV swarm  10  fly in close coordination with the aircraft  16 , with each UAV  12  performing its own designated subtasks within the scope of a broader mission, the UAV swarm initialized as a web of trust as set forth herein may be used to support a wide range of beneficial missions. 
     By way of example and not limitation, representative mission tasks include package delivery operations in which the UAVs  12  of the UAV swarm  10  collectively fly down to a location on the ground surface  20  of  FIG. 1  to deliver packages or mail to different addresses, then return to the aircraft  16  or land on the ground surface  20  at a designated landing site. Alternatively, the UAV swarm  10  could collectively perform an aerial light display, with the constituent UAVs  12  each equipped with lights and configured to fly as part of an ensemble during such a performance. These and other missions require secure encrypted communications in real-time between the various UAVs  12  constituting the UAV swarm  10  of  FIG. 1 , which in turn requires verification of every individual platform-specific identification key in the UAV swarm. The secure exchange of such keys when initializing the web of trust is thus enabled via execution of the method  50  as set forth herein. 
     While some of the best modes and other embodiments have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims. Those skilled in the art will recognize that modifications may be made to the disclosed embodiments without departing from the scope of the present disclosure. Moreover, the present concepts expressly include combinations and sub-combinations of the described elements and features. The detailed description and the drawings are supportive and descriptive of the present teachings, with the scope of the present teachings defined solely by the claims.