Method and system for privacy preserving, face based access control

Abstract

A computer-implemented method of controlling a user access barrier using biometric data is provided. The method comprises an enrolment phase, an access request phase, and an access verification phase. The enrolment phase includes the steps: obtaining biometric data comprising a facial image of a user; generating, using the biometric data, a public key and a privacy preserving data structure; storing the public key in a first data storage location accessible by an authenticator device; and storing the privacy preserving data structure in a second data storage location accessible by a mobile device. The access request phase includes the steps: retrieving on the mobile device the privacy preserving data structure from the second data storage location; obtaining subsequently acquired biometric data comprising the facial image of the user; generating a private key from the privacy preserving data structure on the mobile device using the subsequently acquired biometric data; creating a digital signature using the private key; transmitting the digital signature from the mobile device to the authenticator device. The access verification phase includes the steps: retrieving the public key from the first data storage location to the authenticator device; authenticating on the authenticator device, using the retrieved public key, whether or not the digital signature belongs to the user; and removing the user access barrier in response to authenticating that the digital signature belongs to the user.

Description

METHOD AND SYSTEM FOR PRIVACY PRESERVING, FACE BASED ACCESS CONTROL

[0001] This application claims priority from SG 10202301055W filed 15 April 2023, the contents and elements of which are herein incorporated by reference for all purposes.Field of the Invention

[0002] The present invention relates to computer-implemented methods, devices, and systems for controlling a user access barrier, particularly, although not necessarily exclusively, using biometric data.Background

[0003] Biometric access control systems identify users by their unique biological features. These systems provide an effective means of user authentication without requiring the user to recall a password or unique identifying information.

[0004] In traditional biometric access control, users enrol on the system by supplying a biometric sample such as fingerprints, facial features, voices, and iris patterns. A feature template is generated from the biometric sample and stored in a database as biometric data. Later, when the user presents another biometric sample, a new feature template is generated and compared with the previously stored template. If the respective feature templates are found to be similar, the system deems that the same person supplied each sample. In this regard, the feature templates are ‘linkable’. The ability to compare feature templates with one another is also what makes the stored data biometric in nature. However, in the context of data protection, this is an undesirable property of biometric data because it prevents privacy preservation.

[0005] It is usually possible to obtain the original biometric sample that was used to generate the biometric data stored in the system. Traditional systems necessitate storage of biometric data at a central location accessible by edge devices, allowing the edge devices to match the newly generated feature template against the feature template stored at the central location. Thus, the identities of users may become compromised to third parties without permission.

[0006] Another concern with traditional methods of biometric access control is that it is only possible to generate one feature template from a single biometric sample. This is analogous to having a password that cannot be changed, which currently limits the use of biological features as authentication tools.

[0007] Additionally, traditional biometric verification methods determine a similarity score between two templates. This similarity score makes traditional technology susceptible to ‘Hill Climbing Attacks’, which undermines the integrity of user authentication.

[0008] Traditional systems may also require users to touch part of the edge device such as a fingerprint scanner in order to supply the biometric sample. This presents a high risk of bacterial contamination ofthe edge device leading to the transmission of bacteria between users. Face-based access control systems avoid this by using a face scanning terminal device with one or more cameras to scan the face. However, this increases the cost of the terminal device, and it is inconvenient for some users to position their face at a height required for the system’s camera to scan their face.

[0009] The present invention has been devised in light of the above considerations.Summary of the Invention

[0010] Broadly, the present invention relates to systems and methods for controlling a user access barrier. In particular, biometric data comprising a facial image of a user is used to generate a public key and a privacy preserving data structure which can be used to generate a corresponding private key. The corresponding private key can only be generated from the privacy preserving data structure using subsequently acquired biometric data comprising the facial image of the user that was used to generate the privacy preserving data structure. Therefore, the privacy preserving data structure enables the user to protect the private key using their biometric data by ensuring that the corresponding private key can only be generated at run time from the user’s face. The privacy preserving data structure may store entropy which is used in conjunction with the subsequently acquired biometric data to generate the private key. The privacy preserving data structure may contain encrypted metadata relating to the user which can only be decrypted using the corresponding private key. Although an ‘incorrect’ private key may be generated using a different facial image, the incorrect private key would not be able to decrypt the encrypted metadata stored in the privacy preserving data structure.

[0011] There are multiple known ways to generate such a privacy preserving data structure having these properties. For example, some common approaches are set out in international standard ISO / IEC 30136:2018 the contents of which is incorporated herein by reference. Commercial offerings are available for practitioners in the field to utilise such privacy preserving data structures for achieving the purpose of this invention.

[0012] Accordingly, presented below are different developments of the present invention, identified as Developments A and B. Each of these has different aspects and different optional features, however these developments, aspects and optional features are combinable in any combination unless the context demands otherwise.Development A

[0013] In a first aspect of development A there is provided a computer-implemented method of controlling a user access barrier using biometric data, the method comprising an enrolment phase, an access request phase, and an access verification phase.

[0014] The enrolment phase includes:(i) obtaining biometric data comprising a facial image of a user;(ii) generating, using the biometric data, a public key and a privacy preserving data structure;(iii) storing the public key in a first data storage location accessible by an authenticator device; and(iv) storing the privacy preserving data structure in a second data storage location accessible by a mobile device.

[0015] The access request phase includes:(v) retrieving on the mobile device the privacy preserving data structure from the second data storage location;(vi) obtaining subsequently acquired biometric data comprising the facial image of the user;(vii) generating a private key from the privacy preserving data structure on the mobile device using the subsequently acquired biometric data;(viii) creating a digital signature using the private key;(ix) transmitting the digital signature from the mobile device to the authenticator device.

[0016] The access verification phase includes:(x) retrieving the public key from the first data storage location to the authenticator device;(xi) authenticating on the authenticator device, using the retrieved public key, whether or not the digital signature belongs to the user; and(xii) removing the user access barrier in response to authenticating that the digital signature belongs to the user.

[0017] By using the privacy preserving data structure, only the user is able to generate their private key- i.e. the private key corresponding to the public key. Therefore, a verifier operating the authenticator device can be certain that the digital signature transmitted to the authenticator device belongs to the user.

[0018] While the use of biometric data comprising the facial image of the user is preferred, other types of biometric data are contemplated. For example, the biometric data may comprise, in any combination, one or more of: a fingerprint scan, a palm-print scan, an iris scan, a retina scan, a voice recording, gait characteristics, and a DNA profile. As such, the biometric sensor may be a camera, a fingerprint scanner, or a microphone. Advantageously, the privacy preserving data structure does not store any biometric data so the user can store the privacy preserving data structure at a central location while maintaining exclusive control over their biometric data.

[0019] The user access barrier may form part of an access device. The access device may comprise an on-board controller comprising one or more processors. The access device may comprise an actuator electrically connected to the on-board controller for removing the user access barrier. Preferably, the authenticator device forms part of the access device, e.g. the on-board controller may form part of the authenticator device.

[0020] Alternatively, the authenticator device may control the user access barrier remotely, e.g. by a remote connection to the access device.

[0021] The user access barrier may be a physical barrier, e.g. a turnstile, a gate, or a door. The physical barrier may control user access to a secured area. For example, the physical barrier may have an activated configuration in which user access to the secured area is prevented, and a deactivated configuration in which user access to the secured area is permitted. The physical barrier may be locked in the activated configuration, thereby preventing the user from moving the physical barrier for gaining access to the secured area. The physical barrier may be unlocked in the deactivated configuration, thereby allowing the user to move the physical barrier for gaining access to the secured area. Therefore, removing the user access barrier may include unlocking the physical barrier. Additionally, or alternatively, removing the user access barrier may include moving the physical barrier from an obstructing position to a non-obstructing position for the user with respect to the secured area.

[0022] While preferred embodiments include a physical barrier, it is contemplated that the user access barrier may be a digital barrier such as a device screen lock, app lock, or a folder lock. As such, removing the user access barrier may comprise allowing user access to secured data.

[0023] In the enrolment phase, the biometric data may be obtained using a biometric sensor on the mobile device. As such, the public key and the privacy preserving data structure may be generated by the mobile device.

[0024] Alternatively, the biometric data may be obtained using a biometric sensor of another computing device. For example, the other computing device may be a second mobile device, a desktop computer, a laptop computer, or a tablet computer. As such, the public key and the privacy preserving data structure may be generated by the other device.

[0025] Advantageously, there is no requirement for a biosensor, such as a camera, to be provided at the user access barrier because the user can instead operate the biosensor on the mobile device. This may be more convenient for the user by avoiding the user having to share a biosensor. Additionally, the operator of the user access barrier may reduce costs as they are not required to manufacture and maintain a biosensor device. Further still, the user can maintain exclusive control over their biometric data because there is no need to submit a biometric sample to the authenticator device or, in fact, any device which does not belong to the user.

[0026] The enrolment phase may include transmitting the privacy preserving data structure to the second data storage location. The second data storage location accessible by the mobile device may be a memory of the mobile device. Alternatively, the second data storage location accessible by the mobile device may comprise a central database stored on a remote server, e.g. a cloud server.

[0027] Preferably, the enrolment phase includes assigning an enrolment ID to the public key and / or the privacy preserving data structure. Conveniently, the enrolment ID allows the public key and / or the privacy preserving data structure to be uniquely identified. The enrolment ID may be stored with the public key in the first data storage location. The enrolment ID may be stored with the privacy preserving data structure in the second data storage location.

[0028] The first data storage location may comprise a public key registry. The public key registry may be a central public key registry stored on a remote server. The authenticator device may be an edge device having a network interface configured to communicate with the remote server. The network interface may comprise an on-board wired or wireless network port configured to receive public key registry data.

[0029] Retrieving the public key from the first data storage location may include downloading a list of one or more public keys from the central public key registry to a memory of the authenticator device. The on-board controller of the authenticator device may be configured to store the public key data in the memory of the authenticator device.

[0030] The memory of the authenticator device may store a local public key registry. Therefore, retrieving the public key from the first data storage location may include synchronising the local public key registry stored on the authenticator device with the central public key registry stored on the remote server. Advantageously, the authenticator device does not require constant network connectivity and the authenticator device does not require network connectivity during the access verification phase.

[0031] In some embodiments, the enrolment phase may include assigning a list of one or more permitted barrier IDs to the public key and storing the public key in the central public key registry with the corresponding list of one or more permitted barrier IDs. Accordingly, synchronising the local public key registry with the central public key registry may include transmitting a barrier ID of the user access barrier to the remote server and, subsequently, transmitting to the authenticator device at least part of the central public key registry which comprises any public key for which the transmitted barrier ID is on the list of one or more permitted barrier IDs. This limits whether or not the public key can be downloaded to the memory of the authenticator device based on the user access barrier. Advantageously, where the authenticator device forms part of the access device, this allows permissions to be set for the user to determine which user access barriers can be removed by the user.

[0032] The (e.g. central) public key registry and / or the local public key registry may be configured to store each public key using the respective enrolment ID as a reference. In the access request phase, transmitting the digital signature to the authenticator device may include transmitting the digital signature with the enrolment ID. Therefore, the access verification phase may include retrieving the public key from the first data storage location by reference to the enrolment ID. This improves the efficiency of the authentication process. Specifically, the authenticator device does not have to check the digital signature with each key in a stored list of public keys.

[0033] Where the second data storage location comprises the central database, the step of retrieving the privacy preserving data structure may include retrieving the privacy preserving data structure from the central database by reference to the enrolment ID.

[0034] Although the first data storage location comprises the central public key registry in preferred embodiments, it is also contemplated that the first data storage location may be a memory of theauthenticator device. As such, storing the public key in the first data storage location may include transmitting the public key to the authenticator device directly.

[0035] Creating the digital signature using the private key may include digitally signing a message using the private key. Authenticating whether or not the digital signature belongs to the user, therefore, may include using the retrieved public key and the message to verify whether or not the digitally signature was created using the private key. Digitally signing the message may include encrypting the message or generating a hash of the message using a hashing algorithm and encrypting the hash. Therefore, the digital signature may be an encrypted message or an encrypted hash of the message. Where the digital signature is the encrypted hash, the authenticator device may generate an identical copy of the hash using the same hashing algorithm and the same message. The authenticator device may decrypt the digital signature using the public key and compare the decrypted signature with the message or the hash. The public key will only be able to decrypt the signature if the corresponding private key was used in its encryption. Therefore, the authenticator device may verify whether or not the mobile device holds the private key based on this comparison. As such, the authenticator device may determine that the mobile device holds the private key if the decrypted signature is identical to the message or the hash.

[0036] The message may be a challenge (i.e. a random value or cryptographic nonce) generated by the authenticator device. For example, the method may include generating the challenge on the authenticator device and broadcasting the challenge to the mobile device. Therefore, creating the digital signature may include digitally signing the challenge using the private key generated on the mobile device.

[0037] The challenge may be an ephemeral challenge. Advantageously, the ephemeral challenge protects against eavesdropping by bad actors with a subsequent replay attack. For example, the authenticator device may generate a new challenge to overwrite or replace the preceding challenge and broadcast the new challenge. The preceding challenge may be permanently deleted by the authenticator device when the new challenge is generated.

[0038] The authenticator device may generate the new challenge periodically. Each new challenge may be generated at periodic intervals of not more than 60 seconds, e.g. not more than 40 seconds, e.g. not more than 20 seconds, e.g. not more than 15 seconds, e.g. not more than 10 seconds.

[0039] The authenticator device may generate the new challenge after authenticating that the digital signature belongs to the user, e.g. after removing the user access barrier, e.g. after re-activating the user access barrier.

[0040] The access device may comprise a display, e.g. a screen. As such, broadcasting the challenge may include broadcasting the challenge on the display, e.g. near the user access barrier. Receiving the challenge on the mobile device may include scanning the display using a camera on the mobile device. By broadcasting the challenge via the display, the mobile device must be positioned in a specific location in order to receive the challenge, e.g. facing the display in the vicinity of the user access barrier. Therefore, the display may be positioned such that only one user is able to receive the challenge at anyone time, and / or the user is required to approach the user access barrier in order to receive the challenge.

[0041] Generating the challenge may include encoding the challenge. As such, broadcasting the challenge on the display may include displaying the encoded challenge on the display. Receiving the challenge on the mobile device may further include decoding the challenge from the scanned encoded challenge. The encoded challenge may comprise a barcode or a QR code. The encoded challenge may incorporate additional data instructing the mobile device to retrieve the privacy preserving data structure and / or to obtain the subsequently acquired biometric data.

[0042] While in preferred embodiments the challenge is generated and broadcast by the authenticator device, it is contemplated that the message may be a predetermined message. For example, the predetermined message may correspond to the barrier ID of the user access barrier. This avoids the step of broadcasting the message (i.e. the unencrypted message) to the mobile device, allowing the authenticator device or the access device to be simplified. The user may input the barrier ID to the mobile device.

[0043] The access device may comprise a communications interface. The communications interface may include a wireless transceiver configured to communicate with the mobile device using a wireless network protocol, e.g. NFC, Wi-Fi, Bluetooth. Preferably, the communications interface is configured to receive the digital signature from the mobile device. The communications interface may be configured to broadcast the challenge to the mobile device. The communications interface may be configured to receive the public key directly from the mobile device or the other computing device. The on-board controller may be configured to operate the communications interface.

[0044] The mobile device and / or the other computing device may comprise a communications interface. The communications interface(s) may be configured to transmit and / or receive enrolment data. The enrolment data may comprise one or more of: the public key, the privacy preserving data structure; the enrolment ID; and the list of one or more permitted barrier IDs. The communications interface(s) may include a network interface configured to transmit enrolment data to a remote server, e.g. cloud storage.

[0045] The access verification phase may include providing feedback to the user indicating whether or not user access is granted. For example, the feedback may indicate the status of the user access barrier. When the user access barrier is removed, the feedback may include an indication to the user that the user access barrier has been removed. The access verification phase may include providing feedback to the user indicating that the user access barrier has not been removed when the authenticator device is unable to authenticate that the digital signature belongs to the user. Where the access device includes the display, the feedback may be provided on the display.

[0046] The method may include re-activating the user access barrier after a predetermined time duration has elapsed since removing the user access barrier. Alternatively, or additionally, the method may include re-activating the user access barrier in response to a user input. Re-activating the user access barrier may include locking the physical barrier. Additionally, or alternatively, re-activating the useraccess barrier may include moving the physical barrier from the non-obstructing position to the obstructing position.

[0047] The method may include generating one or more additional public keys using the biometric data, each public key being associated with a string, e.g. a barrier ID. For example, each public key may be associated with a different string. Alternatively, or additionally, the method may include generating a plurality of public keys associated with the same string.

[0048] The method may include generating at least one additional private key from the privacy preserving data structure using subsequently acquired biometric data comprising the facial image of the user. Each private key may be generated for a corresponding public key using a string associated with the corresponding public key. A private key may be generated for a plurality of corresponding public keys using a string associated with the plurality of corresponding public keys. By generating multiple key-pairs from the same privacy preserving data structure, each key-pair may be used to control a different user access barrier. Specifically, the user may distribute different public keys to different authenticator devices for authenticating the user. As such, the user may generate a corresponding private key from the privacy preserving data structure as required for a particular authenticator device. Advantageously, generating new key-pairs using the biometric data of the user improves security.

[0049] In a second aspect of the development A there is provided a system for controlling a user access barrier using biometric data, the system comprising: a key-pair generating device having a communications interface and a first biometric sensor; a mobile device having a second biometric sensor; an authenticator device; and a user access barrier controlled by the authenticator device.

[0050] The key-pair generating device is configured to: obtain biometric data comprising a facial image of a user via the biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure; transmit the public key via the communications interface to a first data storage location accessible by the authenticator device; and store the privacy preserving data structure in a second data storage location accessible by the mobile device.

[0051] The mobile device is configured to: retrieve the privacy preserving data structure from the second data storage location to the mobile device; obtain subsequently acquired biometric data comprising the facial image of the user via the second biometric sensor; generate the private key from the privacy preserving data structure using subsequently acquired biometric data comprising the facial image of the user; create a digital signature using the private key; and transmit the digital signature to the authenticator device.

[0052] The authenticator device is configured to: retrieve the public key from the first data storage location; authenticate, using the retrieved public key, whether or not the digital signature belongs to the user; and remove the user access barrier in response to authenticating that the digital signature belongs to the user.

[0053] In a third aspect of the development A there is provided a key-pair generating device comprising: a biometric sensor, a communications interface, one or more processors, and a memory containingmachine executable instructions which, when executed on the one or more processors, cause the one or more processors to: obtain biometric data comprising a facial image of a user via the biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure from which a private key can be generated; transmit the public key via the communications interface to a first data storage location for access by an authenticator device; and store the privacy preserving data structure in a second data storage location for access by a mobile device.

[0054] In a fourth aspect of development A there is provided a mobile device comprising: a biometric sensor, a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: retrieve a privacy preserving data structure generated using biometric data comprising a facial image of a user; obtain subsequently acquired biometric data comprising the facial image of the user via the biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; create a digital signature using the private key; and transmit the digital signature to an authenticator device via the communications interface.

[0055] In a fifth aspect of development A there is provided an authenticator device for controlling a user access barrier, the authenticator device comprising: a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: retrieve a public key, wherein the public key has a corresponding private key generated using biometric data comprising a facial image of a user; receive a digital signature from a mobile device via the communications interface, the digital signature created using the private key; authenticate, using the retrieved public key, whether or not the digital signature belongs to the user; and remove the user access barrier in response to authenticating that the digital signature belongs to the user.

[0056] The system according to the second aspect may be derived by combining the key-pair generating device of the third aspect, the mobile device of the fourth aspect, and the authenticator device of the fifth aspect.

[0057] In some embodiments, the key-pair generating device is the mobile device. As such, the first biometric sensor may be the second biometric sensor. In other words, the same biometric sensor may be used to obtain the biometric data and the subsequently acquired biometric data.

[0058] The system of the second aspect, the key-pair generating device of the third aspect, the mobile device of the fourth aspect, and the authenticator device of the fifth aspect may be configured to perform any one, or any combination insofar as they are compatible, of the optional features set out with reference to the first aspect.

[0059] Further aspects of development A provide: a computer program comprising code which, when run on a computer, causes the computer to perform the steps of at least one of: the enrolment phase, the access request phase, and the access verification phase of the method of the first aspect; and a computer readable medium storing a computer program comprising code which, when run on a computer, causes the computer to perform the steps of at least one of: the enrolment phase, the access request phase, and the access verification phase of the method of the first aspect.Development B

[0060] In a first aspect of development B there is provided a computer-implemented method of controlling a user access barrier using biometric data, the method comprising: obtaining biometric data comprising a facial image of a user; generating, using the biometric data, a public key and a privacy preserving data structure; encrypting, using the public key, an access code for removing the user access barrier; storing the encrypted access code in a first data storage location accessible by a mobile device and storing the privacy preserving data structure in a second data storage location accessible by the mobile device; retrieving to the mobile device the encrypted access code from the first data storage location and the privacy preserving data structure from the second data storage location; generating a private key from the privacy preserving data structure on the mobile device using biometric data comprising a subsequently acquired facial image of the user; decrypting the encrypted access code on the mobile device using the private key; and removing the user access barrier using the decrypted access code.

[0061] By encrypting the access code using the public key, the access code can be protected to prevent other users being able to remove the user access barrier. Even if the encrypted access code is obtained by another user, the user access barrier cannot be removed by the other user without the private key. This is because the access code must be decrypted first using the private key. Further still, by using the privacy preserving data structure to protect the private key, only the user is able to generate the private key. This provides an additional layer of security for protecting the access code. Even if another user obtains possession of the privacy preserving data structure and the encrypted access code, the access code cannot be decrypted by the other user because the private key must be generated first by the user.

[0062] The user access barrier may be a physical barrier. The user access barrier may form part of an access device such, as a smart lock. As such the access code may be a lock secret. For example, the smart lock may be part of an access system of a hotel room or smart building, e.g. comprising a plurality of smart locks. Advantageously, the smart lock is not required to have any network connectivity in order to manage user accessibility. This avoids the cost of deploying network connected locks.

[0063] The access device may comprise an on-board controller comprising one or more processors. The access device may comprise an actuator electrically connected to the on-board controller for removing the user access barrier.

[0064] The biometric data may be obtained using a biometric sensor on the mobile device. Therefore, the public key and the privacy preserving data structure may be generated by the mobile device.

[0065] Alternatively, the biometric data may be obtained using a biometric sensor of another computing device. For example, the other computing device may be a second mobile device, a desktop computer, a laptop computer, or a tablet computer. As such, the public key and the privacy preserving data structure may be generated by the other device.

[0066] Advantageously, there is no requirement for a biosensor, such as a camera, to be provided at the user access barrier because the user can instead operate the biosensor on the mobile device. This may be more convenient for the user by avoiding the user having to share a biosensor. Additionally, the operator of the user access barrier may reduce costs as they are not required to manufacture and maintain a biosensor device. Further still, the user can maintain exclusive control over their biometric data because there is no need to submit a biometric sample to any device which does not belong to the user.

[0067] The method may include transmitting the encrypted access code to the first data storage location. Preferably, the first data storage location accessible by the mobile device comprises a central database.

[0068] The method may include assigning an enrolment ID to the encrypted access code. Conveniently, the enrolment ID allows the encrypted access code to be uniquely identified. The enrolment ID may be stored with the encrypted access code in the first data storage location.

[0069] The central database may be configured to store each encrypted access code using the respective enrolment ID as a reference. Therefore, the method may include retrieving the encrypted access code from the central database by reference to the enrolment ID, thereby improving efficiency. The central database may be stored on a remote server or in the memory of another computing device.

[0070] Alternatively, the first data storage location may be a memory of the mobile device.

[0071] The access code may be hidden from the user at all times. The mobile device may be prevented from downloading the access code, e.g. the encrypted access code and / or the decrypted access code, to a mobile device storage. For example, the encrypted access code and / or the decrypted access code may only be stored in a random-access memory (RAM) of the mobile device. As such, copies of theencrypted access code and / or the decrypted access code may be deleted, e.g. when the mobile application is not in use.

[0072] Preferably, the second data storage location is a memory of the mobile device.

[0073] Alternatively, the second data storage location accessible by the mobile device may comprise a central registry for storing the privacy preserving data structure, e.g. on a remote server. The method may include transmitting the privacy preserving data structure to the second data storage location.

[0074] The method may include generating a second public key and a second privacy preserving data structure from which a second private key can be generated, using newly acquired biometric data comprising the facial image of the user, and encrypting the access code using the second public key. The method may further include replacing the encrypted access code encrypted by the first public key with the encrypted access code encrypted by the second public key in the first data storage location. The method may include replacing the privacy preserving data structure with the second privacy preserving data structure in the second data storage location. The enrolment ID or a newly generated enrolment ID may be assigned to the encrypted access code encrypted by the second public key.

[0075] The newly acquired biometric data may be obtained using the biometric sensor on the mobile device. Therefore, the second public key and the second privacy preserving data structure may be generated by the mobile device. Alternatively, the newly acquired biometric data may be obtained using a biometric sensor of another computing device.

[0076] The method may include generating one or more additional public keys using the biometric data, each public key being associated with a string, e.g. a barrier ID or a lock ID. For example, each public key may be associated with a different string. Alternatively, or additionally, the method may include generating a plurality of public keys associated with the same string. The method may further include generating at least one additional private key from the privacy preserving data structure using subsequently acquired biometric data comprising the facial image of the user. Each private key may be generated for a corresponding public key using a string associated with the corresponding public key. A private key may be generated for a plurality of corresponding public keys using a string associated with the plurality of corresponding public keys. By generating multiple key-pairs from the same privacy preserving data structure, each key-pair can be used to protect a different access code, e.g. corresponding to a different user access barrier. Furthermore, generating new key-pairs with the user’s face improves security in the event that a private key is compromised.

[0077] The access device may comprise a first communications interface configured to receive the access code from the mobile device. The mobile device may comprise a second communications interface configured to transmit the access code to the access device.

[0078] The first and / or second communications interface(s) may be a wireless transceiver configured to communicate with the mobile / access device using a wireless network protocol, e.g. NFC, Wi-Fi, Bluetooth.

[0079] In a second aspect of development B, there is provided a system for controlling a user access barrier using biometric data, the system comprising: a key-pair generating device having a first biometric sensor; a mobile device having a second biometric sensor; and a user access barrier, wherein the key-pair generating device is configured to: obtain biometric data comprising a facial image of a user via the first biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure; encrypt, using the public key, an access code for removing the user access barrier; store the encrypted access code in a first data storage location accessible by the mobile device; and store the privacy preserving data structure in a second data storage location accessible by the mobile device, wherein the mobile device is configured to: retrieve the encrypted access code from the first data storage location; retrieve the privacy preserving data structure from the second data storage location; obtain subsequently acquired biometric data comprising the facial image of the user via the second biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; and decrypt the encrypted access code using the private key.

[0080] In a third aspect of development B, there is provided a key-pair generating device comprising: a biometric sensor, a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: obtain biometric data comprising a facial image of a user via the biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure in which a private key is encrypted; encrypt, using the public key, an access code for removing a user access barrier; store the encrypted access code in a first data storage location accessible by a mobile device; and store the privacy preserving data structure in a second data storage location accessible by the mobile device.

[0081] In a fourth aspect of development B, there is provided a mobile device for controlling a user access barrier, the mobile device comprising a biometric sensor, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to:retrieve a privacy preserving data structure generated using biometric data comprising a facial image of a user; retrieve an encrypted access code encrypted using the public key; obtain subsequently acquired biometric data comprising the facial image of the user via the biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; decrypt the encrypted access code using the private key.

[0082] The system according to the second aspect may be derived by combining the key-pair generating device of the third aspect and the mobile device of the fourth aspect.

[0083] In some embodiments, the key-pair generating device is the mobile device. The first biometric sensor may be the second biometric sensor. In other words, the same biometric sensor may be used to obtain the biometric data and the subsequently acquired biometric data.

[0084] In a fifth aspect of development B, there is provided a computer-implemented method of protecting a lock secret for unlocking a smart lock, the method comprising: generating a public key and a private key; encrypting the lock secret using the public key; storing the encrypted lock secret in a first data storage location accessible by a mobile device and storing the private key in a second data storage location accessible by the mobile device; retrieving to the mobile device the encrypted lock secret from the first data storage location and the private key from the second data storage location; decrypting the encrypted lock secret using the private key on the mobile device; and unlocking the smart lock using the decrypted lock secret.

[0085] By encrypting the lock secret using the public key, the lock secret can be protected to prevent other users being able to unlock the smart lock. Even if the encrypted lock secret is obtained by another user, the smart lock cannot be unlocked by the other user without the private key. This is because the lock secret must be decrypted first using the private key. Advantageously, the smart lock is not required to have any network connectivity in order to manage user accessibility.

[0086] In the fifth aspect, the method may include: obtaining biometric data comprising a facial image of a user and generating, using the biometric data, the public key and a privacy preserving data structure; and generating the private key from the privacy preserving data structure using subsequently acquired biometric data comprising the facial image of the user.

[0087] The system of the second aspect, the key-pair generating device of the third aspect, the mobile device of the fourth aspect, and the computer-implemented method of the fifth aspect may be configured to perform any one, or any combination insofar as they are compatible, of the optional features set out with reference to the first aspect.

[0088] Further aspects of development B provide: a computer program comprising code which, when run on a computer, causes the computer to perform the method of the first aspect or fifth aspect; and a computer readable medium storing a computer program comprising code which, when run on a computer, causes the computer to perform the method of the first aspect or fifth aspect.Brief Description of the Figures

[0089] Embodiments of the invention will now be discussed by way of example with reference to the accompanying figures in which:Figure 1 shows a schematic representation of a user access control system according to development A.Figure 2 shows a schematic representation of a mobile device according to development A.Figure 3 shows a schematic representation of an access device according to development A.Figure 4 shows an external front view of the access device of Figure 3.Figure 5 shows a flow chart of the steps of a method of controlling a user access barrier using biometric data according to development A.Figure 6 shows a flow chart of the steps of an enrolment phase of the method of Figure 5.Figure 7 shows a flow chart of the steps of an access request phase of the method of Figure 5.Figure 8 shows a flow chart of the steps of an access verification phase of the method of Figure 5.Figure 9 shows a flow chart of the steps of a synchronisation process in the method of Figure 5.Figure 10 shows a flow chart of the steps involving an enrolment ID in the method of Figure 5.Figure 11 shows a flow chart of the steps of a challenge-response protocol in the method of Figure 5.Figure 12 shows a schematic representation of a user access control system according to development B.Figure 13 shows a schematic representation of a mobile device according to development B.Figure 14 shows a schematic of an access device according to development B.Figure 15 shows a flow chart of the initial steps of a method of controlling a user access barrier using biometric data according to development B.Figure 16 shows a flow chart of the subsequent steps in the method of Figure 15.Figure 17 shows a flow chart of the steps involving an enrolment ID in the method of Figures 15 and 16.Figure 18 shows a flow chart of additional steps in the method of Figures 15 and 16 which are performed to reissue a private-public key pair.Detailed Description of the Embodiments

[0090] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0091] Figure 1 shows a schematic representation of a user access control system 100 including a mobile device 120 operated by a user, an access device 140 and a remote server 160 connected to one another over a network.

[0092] Figure 2 shows a schematic representation of the mobile device 120, which is typically a smartphone belonging to the user. As such, the mobile device 120 has a biometric sensor 122 which can be used to obtain a facial image of the user. A built-in camera, such as a front-facing camera, can be used as the biometric sensor 122. The mobile device 120 also has a communications interface 124 including a network interface which is configured to transmit enrolment data to the remote server 160, as discussed in detail below. The mobile device 120 also has a processor 126 for running software stored in a memory 128 of the mobile device 120. The software may be installed as a mobile app.

[0093] Figure 3 shows a schematic representation of the access device 140, while Figure 4 shows an external front view of the access device 140. As shown in Fig. 4, the access device 140 includes a physical user access barrier 142 provided by a turnstile. The user access barrier 142 is locked by default to prevent the user from gaining access to a secured area unless the barrier 142 is removed (e.g. it is unlocked or otherwise actuated to allow the user access).

[0094] The access device 140 includes a communications interface 144 which is a wireless transceiver for communicating with the mobile device 120. For example, the communications interface 124 of the mobile device 120 may use an NFC protocol to transmit authentication data to the access device 140.

[0095] The access device 140 also has a display 146 for displaying QR codes 147 which the user is able to scan with the mobile device 120 (i.e. using a smartphone camera) as part of an authentication process (although as noted above this may be omitted where the challenge is issued via the communications interface). Accordingly, the access device 140 includes an authenticator device 148 which is configured to verify authentication data from the user. The authenticator device 148 includes a network interface 150 which communicates with the remote server 160 to access a central public key registry, a processor 152 and a memory 154 which stores a local public key registry 156.

[0096] A method of controlling the user access barrier 142 will now be described in relation to the interactions between the mobile device 120, the access device 140 and the remote server 160.

[0097] Figure 5 shows a flow chart illustrating the main steps of the method, consisting of an enrolment phase (step S1), an access request phase (step S2), and an access verification phase (step S3).

[0098] In this embodiment, the mobile device 120 is also a key-pair generating device. Accordingly, as set out in Figure 6, the enrolment phase includes a first step S11 of obtaining the biometric datacomprising the facial image of the user via the biometric sensor 122 on the mobile device 120. The user may be prompted by the mobile app to photograph their face using the built-in phone camera. Next, in step S12, the mobile device 120 uses the biometric data to generate a public key and a privacy preserving data structure from which a private key can be generated later using other (subsequently) acquired biometric data. The public key is then stored in a first data storage location in step S13. Importantly, the first data storage location is accessible by the authenticator device 148. In step S14, the privacy preserving data structure is stored in a second data storage location accessible by the mobile device 120. In this embodiment, the second data storage location is the memory 128 of the mobile device 120. Step S14 may be performed before, during, or after, step S13.

[0099] Figure 7 shows a flow chart of the steps of the access request phase of the method. This phase corresponds to the user attempting to gain access through the turnstile by removing the barrier 142. Accordingly, the user needs to provide authentication data proving that they are permitted to gain access.

[0100] The access request phase begins in step S21 by the mobile app retrieving the privacy preserving data structure from the memory 128 of the mobile device 120. However, it is only possible to generate a private key which corresponds to the public key using the same biometric data which was used to generate the privacy preserving data structure and the public key in the first place. Therefore, in step S22, subsequently acquired biometric data comprising the facial image of the user is obtained via the biometric sensor 122 on the mobile device 120. The mobile app may prompt the user to take another photograph of their face to acquire the facial image. The private key is then generated from the privacy preserving data structure in step S23.

[0101] With the generated private key now available, the mobile device 120 creates a digital signature using the private key in step S24. Subsequently in step S25, the mobile device 120 transmits the digital signature to the access device 140 as authentication data to be processed by the authenticator device 148.

[0102] Having received the digital signature of the user from the mobile device 120, the authenticator device 148 performs the steps shown in Figure 8 corresponding to the access verification phase. In step S31 , the authenticator device 148 retrieves the user’s public key from the first data storage location. Further details of how the public key is retrieved are described below with reference to Figure 10.

[0103] The public key can be used to verify whether or not the digital signature was created using the corresponding private key. Therefore, in step S32, the authenticator device 148 authenticates the digital signature using the public key. This proves to the authenticator device 148 that the mobile device 120 has access to the private key of the private-public key pair created by the user. However, the identity of the user can be authenticated by the system 100 as a whole, since only the user is able to generate the private key from the privacy preserving data structure on the mobile device 120 using their biometric data.

[0104] In some embodiments, additional private keys may be generated from the privacy preserving data structure using a string, such as a barrier ID, which is associated with the corresponding public key. Therefore, different key-pairs can be used for controlling access to different barriers.

[0105] In a final step S33 of the access verification phase, the authenticator device 148 removes the barrier 142 in response to authenticating that the digital signature belongs to the user.

[0106] In this embodiment, the first data storage location is a central public key registry on the remote sever 160. Therefore, the mobile device 120 transmits the public key to the remote server 160 via the communications interface 124. Figure 9 shows a flow chart of the steps of a synchronisation process by which the local public key registry 156 stored in the memory 154 of the authenticator device 148 is updated by downloading at least part of the central public key registry stored on the remote sever 160.

[0107] The synchronisation process follows a number of preliminary steps in the enrolment phase. In step S131 , a list of permitted barrier IDs are assigned to the public key. The permitted barrier IDs identify user access barriers, including barriers operated by other access devices (not shown), which are permitted to access the public key. The list may be set by the user or by the mobile app based on certain user permissions. In step S132, the list of permitted barrier IDs is transmitted to the remote server 160 and stored with the public key in the central public key registry.

[0108] The local public key registry may be synchronised with the central public key registry at any time, provided that the authenticator device 148 has a suitable network connection to the remote server 160. In this embodiment, the subsequent synchronisation process steps are considered to be part of step S31 , which involves retrieving the public key from the first data storage location in the access verification phase. In step S311 , the authenticator device 148 transmits a barrier ID identifying the user access barrier 142 to the remote server 160. The remote server 160 determines which public keys in the central public key registry have been assigned a permitted barrier ID corresponding to the transmitted barrier ID (step S312). It is possible that none of the public keys which have yet to be downloaded from the central public key registry to the authenticator device 148 will be accessible by the authenticator device 148. This is more likely to be the case if the local public key registry is recently updated, i.e. synchronisation process has only been performed recently.

[0109] In step 313, the remote server 160 transmits any accessible public keys to the authenticator device 148, which receives the accessible public keys via the network interface 150. The network interface 150 includes a network port to configured to receive the public key registry data. As a result of the synchronisation, the local public key registry will contain the public key generated in the enrolment phase provided that the barrier ID of the barrier 142 was assigned to the public key as a permitted barrier ID.

[0110] Figure 10 shows a flow chart of the steps involving an enrolment ID in the method of Figure 5. As part of step S13, an enrolment ID is assigned to the public key (step S131 ’) and transmitted to the remote server 160 to be stored with the public key in the central public key registry (step S132’). Steps S131 and S132 may be combined with steps S131 ’ and S132’, respectively, or they can be performed separately. The enrolment ID allows the public key to be uniquely identified. A copy of the enrolment ID is stored in the memory 128 of the mobile device 120. Therefore, when the digital signature is transmitted to the authenticator device 148 in step S25, the enrolment ID is also transmitted to the authenticator device 148 (step S251). As part of retrieving the public key from the first data storage location in step S31 , theauthenticator device 148 retrieves the public key by reference to the enrolment ID (step S314). In other words, the authenticator device 148 uses the enrolment ID as a shortcut to retrieve the public key from the local public key registry.

[0111] In this embodiment, the digital signature is created as part of a challenge-response protocol for authenticating the user. Figure 11 shows a flow chart of the steps of the challenge-response protocol. In step S241 , the authenticator device 148 generates a challenge which is intended for the user to sign on the mobile device 120 using their private key. The challenge is a cryptographic nonce which is a randomly generated number used just once to ensure that the cryptographic communication sequence between the authenticator device 148 and the mobile device 120 is unique. In step S242, the challenge is encoded in a QR code 147 which is broadcast to the user in step S243 by displaying the QR code 147 on the display 146 of the access device 140.

[0112] In step S244, the QR code 147 is scanned by the mobile device 120. When the QR code 147 has been scanned, the mobile app may prompt the user to follow additional steps. However, the following steps may be performed by the mobile device 120 automatically in response to scanning the QR code. In step S245, the mobile device 120 decodes the challenge from the QR code 147. The challenge is then signed using the generated private key to create the digital signature in step S246. In step S32 in Figure 8, the challenge is used with the public key to verify the digital signature.

[0113] It will be apparent that steps S241 to S245 in Figure 11 may be performed before, during, or after steps S21 to S23 in Figure 7. In fact, scanning the QR code 147 in step S244 may prompt the mobile device 120 to retrieve the privacy preserving data structure from the memory 128 in step S21 .

[0114] Figure 12 shows a schematic representation of a user access control system 200 according to a different embodiment. The system 200 includes a mobile device 220 operated by a user, an access device 240 and a remote server 260. Unlike the access device 140 in the system 100, the access device 240 does not require network connectivity.

[0115] Figure 13 shows a schematic representation of the mobile device 220, which is typically a smartphone belonging to the user. As such, the mobile device 220 has a biometric sensor 222 which can be used to obtain a facial image of the user. A built-in camera, such as a front-facing camera, can be used as the biometric sensor 222. The mobile device 220 also has a communications interface 224 including a network interface which is configured to transmit enrolment data to the remote server 260, as discussed in detail below. The mobile device 220 also has a processor 226 for running software stored in a memory 228 of the mobile device 220. The software may be installed as a mobile app.

[0116] Figure 14 shows a schematic representation of the access device 240. In this embodiment, the access device 240 is a smart lock having a physical user access barrier 242. The barrier 242 is locked by default to prevent the user from gaining access to a secured area, i.e. a locked room, unless the barrier 242 is removed (i.e. unlocked). The access device 240 includes a communications interface 244 which is a wireless transceiver for communicating with the mobile device 220. The communications interface 224 of the mobile device 220 may use an NFC protocol to transmit an access code to the access device 240for removing the barrier 242. The access device includes a processor 252 which controls the communications interface 244 and the barrier 242, and a memory 254 which stores the access code.

[0117] A method of controlling the user access barrier 242 will now be described in relation to the interactions between the mobile device 220, the access device 240 and the remote server 260. The initial steps S1 ’ to S5’ of the method are shown in the flow chart in Figure 15. These initial steps involve using biometric data to protect the access code. Figure 16 shows a flow chart of the subsequent steps in the method whereby the protected access code is used to remove the barrier 242.

[0118] In this embodiment, the mobile device 220 is also a key-pair generating device. Accordingly, as set out in Figure 15, the method includes a first step ST of obtaining the biometric data comprising the facial image of the user via the biometric sensor 222 on the mobile device 220. The user may be prompted by the mobile app to photograph their face using the built-in phone camera. Next, in step S2’, the mobile device 220 uses the biometric data to generate a public key and a privacy preserving data structure from which a private key can be generated later using other (subsequently) acquired biometric data.

[0119] In step S3’ the public key is used to encrypt the access code. Therefore, the access code can only be decrypted using the private key, which is itself ephemeral and can only be generated using the privacy preserving data structure and subsequently obtained biometric data of the user. The encrypted access code is stored in a first data storage location in step S4’ and the privacy preserving data structure is stored in a second data storage location in step S5’. Importantly, the first and second data storage locations are accessible by the mobile device 220. In this embodiment, the second data storage location is the memory 228 of the mobile device 220. The public key may be stored with the privacy preserving data structure. However, as the public key is not required again in the method it may be deleted from the mobile device.

[0120] Turning to Figure 16, the method continues in step S6’ by the mobile app retrieving the encrypted access code on the mobile device 220 from the first data storage location. The encrypted access code does not need to be retrieved until the user intends to remove the user access barrier 242. The mobile app retrieves the privacy preserving data structure from the memory 228 of the mobile device 220 in step S7’. Step S7’ may be performed before, during, or after step S6’.

[0121] It is only possible to generate the private key from the privacy preserving data structure using biometric data from the same user whose original biometric data was used to generate the privacy preserving data structure and the public key in the first place. Therefore, in step S8’, subsequently acquired biometric data comprising the facial image of the user is obtained via the biometric sensor 222 on the mobile device 220. The mobile app may prompt the user to take another photograph of their face to acquire the facial image. The private key is then generated from the privacy preserving data structure in step S9’.

[0122] With the generated private key now available, the mobile device 220 decrypts the encrypted access code using the private key in step S1 O’. Subsequently in step S1 , the barrier 242 is removed bythe access device 240 in response to receiving the access code from the mobile device via the communications interface 244 using the NFC protocol.

[0123] In some embodiments, additional private keys may be generated from the privacy preserving data structure using a string, such as a smart lock ID, which is associated with the corresponding public key. Therefore, different key-pairs can be used for controlling access to different smart locks.

[0124] In this embodiment, the first data storage location is a central database on the remote sever 260. Therefore, the mobile device 220 transmits the encrypted access code to the remote server 260 via the communications interface 224. Figure 17 shows a flow chart of the steps involving an enrolment ID in the method of Figures 15 and 16. As part of step S4’, an enrolment ID is assigned to the public key (step S41 ’) and transmitted to the remote server 260 to be stored with the encrypted access code in the central database (step S42’). A copy of the enrolment ID is stored in the memory 228 of the mobile device 220. The enrolment ID allows the encrypted access code to be uniquely identified. Therefore, as part of retrieving the encrypted access code in step S6’, the mobile device 220 retrieves the encrypted access code by reference to the enrolment ID (step S61 ’). In other words, the mobile device 220 uses the enrolment ID as a shortcut to retrieve the encrypted access code corresponding to the access device 240 from the central database.

[0125] The mobile device 220 is prevented from downloading the encrypted access code and / or the decrypted access code to a storage of the mobile device 220 in order to keep the access code hidden the access code from the user. Any copies of the encrypted access code and / or the decrypted access code stored in the memory 228 (e.g. RAM) of the mobile device may be deleted when the mobile app is not in use.

[0126] Figure 18 shows a flow chart of additional steps in the method which are performed to reissue a private-public key pair to the user. In step S7’ the mobile device 220 obtains the newly acquired biometric data comprising the facial image of the user via the biometric sensor 222 on the mobile device 220. As before, the user may be prompted by the mobile app to photograph their face again using the built-in phone camera. Next, in step S8’, the mobile device 220 uses the newly acquired biometric data to generate a second public key and a second privacy preserving data structure from which a second private key can be generated.

[0127] In step S9’ the second public key is used to encrypt the access code. This encrypted access code can only be decrypted using the second private key - not the original private key. The second private key is itself protected by the second privacy preserving data structure. The new encrypted access code is stored in the first data storage location in step S10’ to overwrite the original encrypted access code. Accordingly, the original encrypted access code is deleted from the central database. Similarly, in step S11 ’ the second privacy preserving data structure is stored in the second data storage location. In so doing, the second privacy preserving data structure overwrites the original privacy preserving data structure. This process allows the access rights of the previous user to be revoked.

[0128] The systems and methods of the above embodiments may be implemented in a computer system (in particular in computer hardware or in computer software) in addition to the structural components and user interactions described.

[0129] The term “computer system” includes the hardware, software and data storage devices for embodying a system or carrying out a method according to the above described embodiments. For example, a computer system may comprise a central processing unit (CPU), input means, output means and data storage. The computer system may have a monitor to provide a visual output display. The data storage may comprise RAM, disk drives or other computer readable media. The computer system may include a plurality of computing devices connected by a network and able to communicate with each other over that network.

[0130] The methods of the above embodiments may be provided as computer programs or as computer program products or computer readable media carrying a computer program which is arranged, when run on a computer, to perform the method(s) described above.

[0131] The term “computer readable media” includes, without limitation, any non-transitory medium or media which can be read and accessed directly by a computer or computer system. The media can include, but are not limited to, magnetic storage media such as floppy discs, hard disc storage media and magnetic tape; optical storage media such as optical discs or CD-ROMs; electrical storage media such as memory, including RAM, ROM and flash memory; and hybrids and combinations of the above such as magnetic / optical storage media.

[0132] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0133] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0134] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0135] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0136] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and“including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0137] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:1 . A computer-implemented method of controlling a user access barrier using biometric data, the method comprising an enrolment phase; an access request phase; and an access verification phase, wherein the enrolment phase includes:(i) obtaining biometric data comprising a facial image of a user;(ii) generating, using the biometric data, a public key and a privacy preserving data structure;(iii) storing the public key in a first data storage location accessible by an authenticator device; and(iv) storing the privacy preserving data structure in a second data storage location accessible by a mobile device, wherein the access request phase includes:(v) retrieving on the mobile device the privacy preserving data structure from the second data storage location;(vi) obtaining subsequently acquired biometric data comprising the facial image of the user;(vii) generating a private key from the privacy preserving data structure on the mobile device using the subsequently acquired biometric data;(viii) creating a digital signature using the private key;(ix) transmitting the digital signature from the mobile device to the authenticator device; wherein the access verification phase includes:(x) retrieving the public key from the first data storage location to the authenticator device;(xi) authenticating on the authenticator device, using the retrieved public key, whether or not the digital signature belongs to the user; and(xii) removing the user access barrier in response to authenticating that the digital signature belongs to the user.

2. The computer-implemented method of claim 1 , wherein the biometric data is obtained using a biometric sensor on the mobile device and the privacy preserving data structure and the public key are generated by the mobile device.

3. The computer-implemented method of claim 2, wherein the second data storage location is a memory of the mobile device.

4. The computer-implemented method of any preceding claim, wherein the first data storage location is a public key registry.

5. The computer-implemented method according to claim 4, wherein the enrolment phase includes assigning an enrolment ID to the public key and storing the enrolment ID with the public key in the public key registry, wherein the access request phase includes transmitting the digital signature with theenrolment ID, wherein the access verification phase includes retrieving the public key from the public key registry by reference to the enrolment ID.

6. The computer-implemented method of claim 4 or claim 5, wherein the public key registry is a central public key registry stored on a remote server and retrieving the public key from the first data storage location includes: synchronising a local public key registry stored on the external device with the central public key registry.

7. The computer-implemented method of claim 6, wherein the method further includes transmitting the public key and the enrolment ID to the remote server with a corresponding list of one or more permitted barrier IDs, wherein synchronising the local public key registry with the central public key registry includes transmitting a barrier ID of the user access barrier to the remote server and, subsequently, transmitting to the authenticator device at least part of the central public key registry comprising any public key and enrolment ID for which the external device ID is a permitted external device ID.

8. The computer-implemented method according to any preceding claim wherein the user access barrier and the authenticator device form part of an access device.

9. The computer-implemented method of claim 8, wherein the method includes generating a challenge on the authenticator device and, broadcasting the challenge to the mobile device, wherein creating the digital signature includes digitally signing the challenge using the private key.

10. The computer-implemented method according to claim 9, wherein the access device comprises a display and broadcasting the challenge to the mobile device includes broadcasting the challenge on the display.

11. The computer-implemented method according to claim 10, wherein the mobile device receives the challenge by scanning the display using a camera on the mobile device.

12. The computer-implemented method according to claim 11 , wherein generating the challenge includes encoding the challenge in a QR code, and broadcasting the challenge on a display includes displaying the QR code on the display, wherein the mobile device decodes the challenge from a scan of the QR code.

13. The computer-implemented method according to any one of claims 9 to 12, wherein the authenticator device generates a new challenge periodically to replace a preceding challenge.

14. The computer-implemented method according to any one of the preceding claims, wherein the user access barrier is a physical barrier.

15. A system for controlling a user access barrier using biometric data, the system comprising: a key-pair generating device having a communications interface and a first biometric sensor; a mobile device having a second biometric sensor; an authenticator device; and a user access barrier controlled by the authenticator device, wherein the key-pair generating device is configured to: obtain biometric data comprising a facial image of a user via the biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure; transmit the public key via the communications interface to a first data storage location accessible by the authenticator device; and store the privacy preserving data structure in a second data storage location accessible by the mobile device, wherein the mobile device is configured to: retrieve the privacy preserving data structure from the second data storage location to the mobile device; obtain subsequently acquired biometric data comprising the facial image of the user via the second biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; create a digital signature using the private key; and transmit the digital signature to the authenticator device, wherein the authenticator device is configured to: retrieve the public key from the first data storage location; authenticate, using the retrieved public key, whether or not the digital signature belongs to the user; and remove the user access barrier in response to authenticating that the digital signature belongs to the user.

16. The system of claim 15, wherein the key-pair generating device is the mobile device.

17. The system according to claim 15 or claim 16, wherein the second data storage location is a memory of the mobile device.

18. The system according to any one of claims 15 to 17, wherein the first data storage location is a public key registry.

19. The system according to claim 18, wherein the key-pair generating device is configured to assign an enrolment ID to the public key and transmit the enrolment ID with the public key to the public key registry, wherein the mobile device is configured to transmit the digital signature with the enrolment ID to the authenticator device, wherein the authenticator device is configured to retrieve the public key from the public key registry by reference to the enrolment ID.

20. The system according of claim 18 or claim 19, wherein the public key registry is a central public key registry stored on a remote server and the authenticator device is configured to synchronise a local public key registry stored on the authenticator device with the central public key registry.

21. The system of claim 20, wherein the key-pair generating device is configured to transmit storing the public key and the enrolment ID to the remote server with a corresponding list of one or more permitted barrier IDs, wherein the authenticator device is configured to synchronise the local public key registry with the central public key registry by transmitting a barrier ID of the user access barrier to the remote server which is configured to transmit to the authenticator device at least part of the central public key registry comprising any public key and enrolment ID for which the external device ID is a permitted external device ID.

22. The system according to any one of claims 15 to 21 wherein the user access barrier and the authenticator device form part of an access device.

23. The system of claim 22, wherein the authenticator device is configured to generate a challenge and broadcast the challenge to the mobile device, wherein the mobile device is configured to digitally sign the challenge using the private key to create the digital signature.

24. The system of claim 23, wherein the access device comprises a display which is configured to broadcast the challenge to the mobile device.

25. The system of claim 24, wherein the mobile device is configured to scan the display using a camera on the mobile device.

26. The system of claim 25, wherein the authenticator device is configured to encode the challenge in a QR code and the display is configured to display the QR code, wherein the mobile device is configured to decode the challenge from a scan of the QR code.

27. The system according to any one of claims 23 to 26, wherein the authenticator device is configured to generate a new challenge periodically to replace a preceding challenge.

28. The computer-implemented method according to any one of the preceding claims, wherein the user access barrier is a physical barrier.

29. A key-pair generating device comprising: a biometric sensor, a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: obtain biometric data comprising a facial image of a user via the biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure from which a private key can be generated; transmit the public key via the communications interface to a first data storage location for access by an authenticator device; and store the privacy preserving data structure in a second data storage location for access by a mobile device.

30. A mobile device comprising: a biometric sensor, a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: retrieve a privacy preserving data structure generated using biometric data comprising a facial image of a user; obtain subsequently acquired biometric data comprising the facial image of the user via the biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; create a digital signature using the private key; and transmit the digital signature to an authenticator device via the communications interface.

31. An authenticator device for controlling a user access barrier, the authenticator device comprising: a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: retrieve a public key, wherein the public key has a corresponding private key generated using biometric data comprising a facial image of a user; receive a digital signature from a mobile device via the communications interface, the digital signature created using the private key; authenticate, using the retrieved public key, whether or not the digital signature belongs to the user; and remove the user access barrier in response to authenticating that the digital signature belongs to the user.

32. A computer-implemented method of controlling a user access barrier using biometric data, the method comprising: obtaining biometric data comprising a facial image of a user;generating, using the biometric data, a public key and a privacy preserving data structure; encrypting, using the public key, an access code for removing the user access barrier; storing the encrypted access code in a first data storage location accessible by a mobile device and storing the privacy preserving data structure in a second data storage location accessible by the mobile device; retrieving to the mobile device the encrypted access code from the first data storage location and the privacy preserving data structure from the second data storage location; generating a private key from the privacy preserving data structure on the mobile device using biometric data comprising a subsequently acquired facial image of the user; decrypting the encrypted access code on the mobile device using the private key; and removing the user access barrier using the decrypted access code.

33. The computer-implemented method of claim 32, the method further including: obtaining newly acquired biometric data comprising the facial image of the user; generating a second public key and a second privacy preserving data structure from which a second private key can be generated, using the newly acquired biometric data, encrypting the access code using the second public key, replacing the encrypted access code encrypted by the first public key with the encrypted access code encrypted by the second public key in the first data storage location, and replacing the privacy preserving data structure with the second privacy preserving data structure in the second data storage location.

34. The computer-implemented method of claim 32 or claim 33, wherein the biometric data is obtained using a biometric sensor on the mobile device and the privacy preserving data structure and the public key are generated by the mobile device.

35. The computer-implemented method according to any one of claims 32 to 34, wherein the second data storage location is a memory of the mobile device.

36. The computer-implemented method according to any one of claims 32 to 35, wherein the first data storage location is a central database.

37. The computer-implemented method according to claim 36, wherein the method includes: assigning an enrolment ID to the encrypted access code and transmitting the enrolment ID with the encrypted access code to the central database, and retrieving the encrypted access code from the central database by reference to the enrolment ID.

38. The computer-implemented method according to any one of claims 32 to 37, wherein the user access barrier is a physical barrier.

39. The computer-implemented method according to any one of claims 32 to 38, wherein the user access barrier forms part of an access device, wherein removing the user access barrier using the decrypted access code includes transmitting the decrypted access code to the access device.

40. A system for controlling a user access barrier using biometric data, the system comprising: a key-pair generating device having a first biometric sensor; a mobile device having a second biometric sensor; and a user access barrier, wherein the key-pair generating device is configured to: obtain biometric data comprising a facial image of a user via the first biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure; encrypt, using the public key, an access code for removing the user access barrier; store the encrypted access code in a first data storage location accessible by the mobile device; and store the privacy preserving data structure in a second data storage location accessible by the mobile device, wherein the mobile device is configured to: retrieve the encrypted access code from the first data storage location; retrieve the privacy preserving data structure from the second data storage location; obtain subsequently acquired biometric data comprising the facial image of the user via the second biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; and decrypt the encrypted access code using the private key.

41. The system of claim 40, wherein the key-pair generating device is the mobile device and the first biometric sensor is the second biometric sensor.

42. The system of claim 40 or claim 41 , wherein the second data storage location is a memory of the mobile device.

43. The system of any one of claims 40 to 42, wherein the first data storage location is a central database.

44. The system according to claim 43, wherein the key-pair generating device is configured to assign an enrolment ID to the encrypted access code and transmit the enrolment ID with the encrypted access code to the central database, and the mobile device is configured to retrieve the encrypted access code from the central database by reference to the enrolment ID.

45. The system according to any one of claims 40 to 44, wherein the user access barrier is a physical barrier.

46. The system according to any one of claims 40 to 45, wherein the user access barrier forms part of an access device, wherein the mobile device is configured to transmit the decrypted access code to the access device to remove the user access barrier.

47. A computer-implemented method of protecting a lock secret for unlocking a smart lock, the method comprising: generating a public key and a private key; encrypting the lock secret using the public key; storing the encrypted lock secret in a first data storage location accessible by a mobile device and storing the private key in a second data storage location accessible by the mobile device; retrieving to the mobile device the encrypted lock secret from the first data storage location and the private key from the second data storage location; decrypting the encrypted lock secret using the private key on the mobile device; and unlocking the smart lock using the decrypted lock secret.

48. A key-pair generating device comprising: a biometric sensor, a communications interface, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: obtain biometric data comprising a facial image of a user via the biometric sensor; generate, using the biometric data, a public key and a privacy preserving data structure from which a private key can be generated; encrypt, using the public key, an access code for removing a user access barrier; store the encrypted access code in a first data storage location accessible by a mobile device; and store the privacy preserving data structure in a second data storage location accessible by the mobile device.

49. A mobile device for controlling a user access barrier, the mobile device comprising a biometric sensor, one or more processors, and a memory containing machine executable instructions which, when executed on the one or more processors, cause the one or more processors to: retrieve a privacy preserving data structure generated using biometric data comprising a facial image of a user; retrieve an encrypted access code encrypted using the public key; obtain subsequently acquired biometric data comprising the facial image of the user via the biometric sensor; generate a private key from the privacy preserving data structure using the subsequently acquired biometric data; decrypt the encrypted access code using the private key.RECTIFIED SHEET (RULE 91) ISA / EP

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