Abstract:
A method for providing evidential data is disclosed. The method includes establishing one or more first secret tokens with a server; obtaining one or more data items from one or more sensors; modifying the one or more data items with at least one of the one or more first secret tokens to provide one or more modified data items; generating a respective first hash value for each of the one or more modified data items; generating a second hash value for a data set including each of the one or more data items; and transmitting the one or more data items, the one or more first hash values, and the second hash value to the server.

Description:
BACKGROUND 
     Mobile computing devices, such as mobile telephones, smartphones, tablet computers, etc., often comprise, or have access to, an array of sensors such as image sensors and sound sensors. While commonly used to record events for personal consumption, such recordings are generally unsuitable for use as evidence in proceedings in which the authenticity, accuracy and/or provenance of those recordings may require verification. 
     The rapid proliferation of mobile devices is such, however, that mobile devices are often present in circumstances in which such evidential data may be usefully obtained. It would therefore be beneficial if such mobile devices were able to obtain and provide evidential quality recordings of transactions or events. Such evidential quality recordings may have uses, for example, in legal proceedings, insurance claims, etc. 
     It is an object of the present invention to obviate or mitigate at least one of the problems of the prior art whether identified herein or elsewhere. 
     SUMMARY 
     According to a first aspect described herein, there is provided a method for providing evidential data, comprising at a mobile device: establishing one or more first secret tokens with a server; obtaining one or more data items from one or more sensors; modifying the one or more data items with at least one of the one or more first secret tokens to provide one or more modified data items; generating a respective first hash value for each of the one or more modified data items; generating a second hash value for a data set comprising each of the one or more data items; and transmitting the one or more data items, the one or more first hash values and the second hash value to the server. 
     The data set may comprise the first hash values. 
     The method may further comprise obtaining one or more transaction identifiers, each transaction identifier being suitable for identifying a property of the mobile device; and transmitting an indication of the transaction identifiers to the server. 
     The data set may comprise one or more of the transaction identifiers. 
     The one or more transaction identifiers may comprise one or more static identifiers, wherein each static identifier is suitable for identifying a static property of the mobile device. 
     Transmitting an indication of the static identifiers to the server may comprise generating a respective third hash value for each of the one or more static identifiers, wherein the indication comprises the third hash values. 
     The data set may comprise the third hash values. 
     Calculating each respective third hash value may comprise modifying each of the plurality of static identifiers with at least one of the one or more first secret tokens and calculating each of the third hash values based upon the modified static identifiers. 
     The transaction identifiers may comprise one or more variable identifiers and each variable identifier may be suitable for identifying a variable property of the mobile device. Transmitting an indication of the variable identifiers to the server may comprise transmitting the variable identifier to the server. 
     The data set may comprise the variable identifiers. 
     The method may further comprise an initialization procedure. The initialization procedure may comprise transmitting a plurality of initialization identifiers to the server. 
     The initialization identifiers may comprise one or more static identifiers and/or one or more variable identifiers. 
     Transmitting a plurality of initialization identifiers may comprise obtaining the plurality of initialization identifiers, encrypting the obtained initialization identifiers and transmitting the encrypted initialization identifiers to the server. 
     The transaction identifiers may be based upon the initialization identifiers to allow comparison at the server between values of the initialization identifiers and the transaction identifiers. 
     The one or more sensors may comprise at least one sensor from the group comprising a camera of the mobile device and a microphone of the mobile device. 
     The one or more data items may comprise one or more still images. 
     The one or more data items may comprise one or more videos. 
     The one or more data items may comprise one or more sound recordings. 
     The one or more static identifiers may comprise at least one identifier from the group comprising an identification number of a battery of the mobile device, an IMEI number of the mobile device, and a telephone number of the mobile device. 
     The one or more variable identifiers may comprise at least one identifier from the group comprising a geographical location of the mobile device, a date and time reported by the mobile device, a duration of time since the mobile device was turned on, an indication of other devices detected by the mobile device, and a file structure of the mobile device. 
     The method may further comprise establishing one or more second secret tokens with the server after transmission of the one or more data items and the first and second hash values. 
     According to a second aspect, there is provided a method for receiving evidential data comprising, at a server: establishing one or more first secret tokens with a mobile device; receiving one or more data items, one or more first hash values, and a second hash value from the mobile device; wherein each of the one or more first hash values are hash values generated based upon a respective one of the one or more data items modified with at least one of the one or more first secret tokens; wherein the second hash value is a hash value generated based upon a data set comprising each of the one or more data items. 
     The method may further comprise modifying each of the received one or more data items with at least one of the one or more first secret tokens; generating a respective first comparison hash value for each of the modified received one or more data items; comparing each respective first comparison hash value to a corresponding one of the first hash values; and providing an indication for each respective first comparison hash value that does not match a corresponding one of the first hash values. 
     Providing an indication may comprise outputting an indication to a display device, or saving an indication together with the data. 
     The method may further comprise receiving a plurality of initialization identifiers from the mobile device; receiving one or more transaction identifiers, each of the one or more transaction identifiers being suitable for identifying a property of the mobile device; and comparing at least one of the initialization identifiers with at least one of the transaction identifiers. 
     The method may further comprise transmitting a request for the transaction identifiers based upon the received initialization identifiers. 
     The initialization identifiers may comprise a first static identifier suitable for identifying a static property of the mobile device. The one or more transaction identifiers may comprise an indication of a corresponding static identifier. Comparing at least one of the initialization identifiers may comprise comparing the first static identifier with the corresponding static identifier. 
     The indication of the static identifier may comprise a third hash value based upon the corresponding static identifier. Comparing the first static identifier with the corresponding static identifier may comprise generating a fourth hash value based on the first static identifier and comparing the fourth hash value with the third hash value. 
     The third hash value may have been generated by the mobile device performing the steps of modifying the corresponding static identifier with at least one of the one or more first secret tokens and calculating each the third hash values based upon the modified corresponding static identifier. Generating the fourth hash value may comprise modifying the first static identifier with at least one of the one or more first secret tokens and calculating the fourth hash value based upon the modified first static identifier. 
     The initialization identifiers may comprise a first variable identifier suitable for indicating variable properties of the mobile device. The received transaction identifiers may comprise a corresponding variable identifier. Comparing the first variable identifier with the corresponding variable identifier may comprise determining whether a difference between the first variable identifier and the second variable identifier are within predetermined bounds. 
     The initialization identifiers may comprise at least one of a number of a battery of the mobile device, an IMEI number of the mobile device, and a telephone number of the mobile device. 
     The one or more variable identifiers may comprise at least one identifier from the group comprising a geographical location of the mobile device, a date and time reported by the mobile device, a duration of time since the mobile device was turned on, an indication of other devices detected by the mobile device, and a file structure of the mobile device. 
     The method may further comprise establishing one or more second secret tokens with the mobile device after receipt of the one or more data items and the first and second hash values. 
     According to a third aspect, there is provided an apparatus for providing evidential data, comprising a memory storing computer readable instructions configured to cause a computer to carry out a method as defined above, and a processor configured to execute the computer readable instructions. 
     It is to be understood that features described with reference to one aspect above may be combined with other aspects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  schematically illustrates an example network of components which may be used to implement an embodiment; 
         FIG. 2A  schematically illustrates an example configuration components which may be used to implement the server of  FIG. 1 ; 
         FIG. 2B  schematically illustrates an example configuration of components which may be used to implement a mobile device of  FIG. 1 ; 
         FIG. 3  is a flowchart showing initiation processing carried out by the server and the mobile device of  FIG. 1 ; 
         FIG. 4  is a flow diagram showing data generated and exchanged between the server and the mobile device while performing the processing of  FIG. 3 ; 
         FIG. 5  is a flowchart showing processing carried out by the mobile device of  FIG. 1  to transmit evidential data; 
         FIG. 6  is a flow diagram showing how the data is bundled while performing the processing of  FIG. 5 ; and 
         FIG. 7  is a flowchart showing processing carried out by the server to receive evidential data from the mobile device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a network of computer devices that can be used to implement embodiments of the present invention. A mobile device  1  connects to a server  2  via a network  3 . The network  3  may be any suitable public or private network and may be, for example, the Internet. The mobile device  1  may take any form suitable for connection to the network  2 . For example, the mobile device  1  may be a mobile telephone, a smartphone, a tablet, etc. 
     The connections between the server  2 , the mobile device  1 , and the network  3  may take any appropriate form and may be wired or wireless connections. It will be appreciated that while a single mobile device  1  is illustrated in  FIG. 1 , this is merely exemplary and any number of mobile devices may connect with the server  2 . 
     The mobile device  1  is configured to provide data to the server  2  via the network  3 . In particular, the mobile device  1  is configured to provide data relating to incidents that occur in the proximity of the mobile device  1 , such as accidents, crimes, etc., for the purpose of evidence. For example, the mobile device  1  may be equipped with recording means such as one or more cameras for recording images or video, microphones for recording sounds, and receivers for recording received radio signals. It will be appreciated that the mobile device  1  may be used to obtain any form of evidential data as required. 
     The mobile device  1  may communicate with the server  2  from within a local computer application operating on the mobile device  1  (or “app”) or via a remote application provided by the server  2  and accessed from the mobile device  1  through, for example, a web browser. Future references to a computer application with which the mobile device  1  may communicate with the server  2  may therefore be either a local computer application or a remote application. 
     Upon obtaining evidential data, the mobile device  1  transmits the evidential data to the server  2  via the network  3 . In particular, the mobile device  1  transmits the evidential data along with further data to allow the server  2  and/or third parties (such as police or judicial authorities) to determine that the evidential data originates from the mobile device  1  and has not been modified, or otherwise tampered, with subsequent to its creation and/or transmission to the server  2 . 
     The server  2  is connected to a public data store  4  and a private data store  5 . The private data store  5  may be isolated from the network  3  to prevent access to files stored thereon by, for example, the mobile device  1 , and any other device. A firewall  6  may be connected between the private data store  5  and the server  2 . 
     The mobile device  1  may operate in the vicinity of one or more location indication devices. As used herein, the term location indication device means any device which may be used to provide indications of the current geographical location of the mobile device  1  or indications of geographical locations through which the mobile device  1  has passed. For example, the mobile device  1  may pass in and out of range of one or more wireless access points or base stations  7 ,  8  (such as WiFi access points and/or WiMAX base stations, for example), one or more global positioning satellites (GPS)  9 , and one or more cellular network antennas  10 . 
       FIG. 2A  shows an exemplary schematic illustration of components which can be used to provide the mobile device  1  in accordance with some embodiments of the present invention. It can be seen that the mobile device  1  comprises a CPU  1   a  which is configured to read and execute instructions stored in a random access memory (RAM)  1   b  which, in this example, takes the form of volatile memory  1   b . It will be appreciated that non-volatile RAM may equally be used in such an embodiment. The RAM  1   b  stores instructions for execution by the CPU  1   a  and data used by those instructions. For example, the instructions loaded into the RAM  1   b  may provide one or more computer programs that are operable to obtain evidential data and to transmit that evidential data to the server  2 . 
     The mobile device  1  further comprises non-volatile storage  1   c , which may take any suitable form, such as, for example, a hard disk drive (HDD) or solid state drive (SSD). Computer readable instructions for facilitating the capture, storage and transmission of evidential data to the server  2  may be stored in the non-volatile storage  1   c.    
     The mobile device  1  further comprises an I/O interface  1   d  to which are connected peripheral devices used in connection with the mobile device  1 . More particularly, a display  1   e  is configured so as to display output from the mobile device  1 . The display  1   e  may be a touchscreen display, allowing a user to provide input to the mobile device  1   e . Other input devices are also connected to the I/O interface  1   d . Such input devices include a camera  1   f  and a microphone  1   g , thereby allowing a user of the mobile device  1  to obtain images (including video and still) and sound. It will be appreciated that other input devices may equally be provided. For example, dedicated biometric scanning means, such as fingerprint scanners, may be provided. 
     A network interface  1   h  allows the mobile device  1  to be connected to appropriate computer networks, such as the network  3 , so as to receive and transmit data from and to other computing devices such as the server  2 . The network interface  1   h  may also allow connection with, or detection of signals from, location indication devices such as the location indication devices  7  to  10 . 
     The CPU  1   a , volatile memory  1   b , RAM  1   c , I/O interface  1   d , and network interface  1   h , are connected together by a bus  1   i.    
     It will be appreciated that the arrangement of components illustrated in  FIG. 2A  is merely exemplary, and that the mobile device  1  may comprise additional or fewer components than those illustrated in  FIG. 2A . 
       FIG. 2B  shows a schematic illustration of components which can be used to provide the server  2  in accordance with some embodiments of the present invention. It can be seen that, at a schematic level, the server  2  may be implemented similarly to the mobile device  1 . In particular, the server  2  may comprise a CPU  2   a  which is configured to read and execute instructions stored in a random access memory (RAM)  2   b . The RAM  2   b  stores instructions for execution by the CPU  2   a  and data used by those instructions. For example, the instructions loaded into the RAM  2   b  may provide one or more computer programs that are operable to facilitate receipt of evidential data from the mobile device  1  and for confirming that the received evidential data is suitable for use as evidence. 
     The server  2  further comprises non-volatile storage  2   c , which may take any suitable form, such as, for example, a hard disk drive (HDD) or solid state drive (SSD). The non-volatile storage  2  may comprise the data stores  4 ,  5 . Alternatively, the data stores  4 ,  5  may be connected to the server  2  via a storage network (not shown). 
     The server  2  further comprises an I/O interface  2   d  to which are connected peripheral devices used in connection with the server  2 . More particularly, a display  2   e  is configured so as to display output from the server  2 . The display  2   e  may be a touchscreen display, allowing a user to provide input to the server  2 . Other input devices may also connected to the I/O interface  2   d , such as a keyboard  2   f . It will be appreciated that other input devices may equally be provided. 
     A network interface  2   h  allows the server  2  to be connected to appropriate computer networks, such as the network  3 , so as to receive and transmit data from and to other computing devices such as the mobile device  1 . 
     The CPU  2   a , volatile memory  2   b , RAM  2   c , I/O interface  2   d , and network interface  2   h , are connected together by a bus  2   i.    
     It will be appreciated that the arrangement of components illustrated in  FIG. 2B  is merely exemplary, and that the server  2  may comprise additional or fewer components than those illustrated in  FIG. 2B . Indeed, the server  2  may comprise a plurality of computers, similar to, or arranged differently from, the mobile device  1 . For example, the server  2  may comprise a plurality of computers respectively adapted to provide, inter alia, a web server, an application server, a gateway server, and a database server, etc., to provide suitable applications to the mobile device  1  over the network  3 . That is, it is to be understood that, like the mobile device  1 , the server  2  may be implemented using any appropriate configuration as will be readily appreciated by those skilled in the art. 
       FIG. 3  is a flowchart illustrating an initialization process that is carried out by the mobile device  1  and the server  2  before transactions for transmission of evidential data between the mobile device  1  to the server  2 .  FIG. 4  schematically illustrates data that is generated and exchanged by the mobile device  1  and the server  2  during the processing of  FIG. 3 . It is assumed that in advance of the processing of  FIG. 3 , a user of the mobile device  1  has registered as a customer or user of a service which receives evidential data. For example, the user of the mobile device  1  may obtain an insurance product, such as vehicle insurance, from an entity that operates the server  2  or on whose behalf the server  2  is operated. In this example, the user  1  may use embodiments described herein to provide evidential data relating to accidents, damage, etc. of a vehicle that is insured. 
     Prior to the processing of  FIG. 3 , the entity with whom the user is registered may provide suitable login details for use of the application. Alternatively, the user may establish login details through a registration process conducted through the application, as will be readily appreciated by the skilled person. 
     At step S 1 , the user of the mobile device  1  enters their login details into a suitable interface provided by the application. At step S 2 , the server  2  receives the user&#39;s login details and validates that the login details belong to a registered account. Following validation of the login details, from step S 1 , processing at the mobile device  1  passes to step S 3 , while processing at the server  2  passes to step S 4 . At steps S 3  and S 4  the mobile device  1  and the server  2  exchange public keys for use with asymmetric cryptography. With reference to  FIG. 4 , the mobile device  1  transmits its public key  15  to the server  2 , while the server  2  transmits its public key  16  to the mobile device  1 . In  FIG. 4 , the server  2  is shown as receiving the public key  15  and the mobile device is shown as receiving the public key  16 . It will be appreciated that this is merely schematic, and that the server  2  will maintain a copy of the public key  15  while the mobile device  1  will maintain a copy of the public key  16 . The mobile device  1  further stores a private key  17  (corresponding to its public key  15 ), while the server  2  stores a private key  18  (corresponding to its public key  16 ). 
     The keys  15 ,  16 ,  17 ,  18  may be generated prior to the processing of  FIG. 3  or may be generated as part of the processing of steps S 3  and S 4 . The public and private keys may be generated using any appropriate means as will be readily apparent to the skilled person. As an example only, the public and private keys may be generated using the RSA algorithm. 
     Upon receipt of the public key  15  from the mobile device  1 , processing at the server  2  passes to step S 5  at which the server  2  generates a unique, randomly generated token  21 . The token  21  is encrypted using the public key  15  received from the mobile device  1  to generate an encrypted token  22  which can only be decrypted using the private key  17  of the mobile device  1 . The token  21  (or data to be sent in combination with the token  21 ) may additionally be signed (not shown in  FIG. 4 ) by the server  2  using the private key  18 . For example, the token  21 , or a hash of the token  21 , may additionally be encrypted using the private key  18  such that the token  21  can only be decrypted by the mobile device  1  using the public key  16  received from the server  2 . In this way, the mobile device  1  can have greater certainty that the token  21  was received from the server  2 , and not a third party. 
     The encrypted token  22  is transmitted to the mobile device  1  and received by the mobile device  1  at step S 7 . The mobile device  1  decrypts the encrypted token  22  using its private key  17  to obtain the token  21 . 
     After the processing of steps S 3  to S 7 , the mobile device  1  and the server  2  each possess information, in the form of the token  21 , known only to each other. It will be appreciated, however, that the processing of steps S 3  to S 7  are merely exemplary, and that in practice any suitable means may be used for the mobile device  1  and the server  2  to securely exchange a suitable token. In other embodiments, for example, a plurality of secret tokens may be exchanged. 
     Processing passes from step S 7  to step S 8  at which the mobile device  1  generates or obtains a plurality of initialization identification data items  25 . Suitable identification data items include, for example, an International Mobile Station Equipment Identity (IMEI) number of the mobile device  1  (or similar identifiers, such as ESN, MEID, etc.), an International Mobile Subscriber Identity (IMSI) number, Service Set Identifier (SSID) history data (i.e., which SSIDs the mobile device  1  has come into contact with), GPS data, an indication of a current local mobile cell, current date and time data, a recorded uptime of the mobile device  1 , a last reboot time of the mobile device  1 , a bit-rate between the mobile device  1  and the server  2 , a file directory structure of the mobile device  1 , etc. That is, it will be appreciated that the identification data may comprise any suitable identification data which can be used by the server  2  to ascertain the authenticity of a device claiming to be the mobile device  1  in future transactions. 
     The identification data may comprise both “static” identifiers and “variable” identifiers. Static identifiers may be identifiers which are not expected to change over time or which are expected to change only infrequently. For example, battery identification numbers, IMEI numbers, file structure data, etc. may be expected to vary infrequently. Variable identifiers may be those identifiers which are expected to change over time. For example, time and data identifiers, location identifiers, SSID history data, etc. may be expected to vary between an initialization and a first transaction, and between respective transactions. 
     As is described below in more detail with reference to  FIGS. 5 and 6 , identifiers may be transmitted to the server  2  from the mobile device  1  during each transaction (i.e., transactions to transmit evidential data). Because static identifiers are not expected to vary frequently, it may not be necessary to re-transmit (after initial transmission during the processing of  FIG. 3 ) each static identifier. Rather, as discussed below, in some embodiments, only a hash value based on each static identifier is transmitted. 
     The particular set of identification data items  25  obtained or generated by the mobile device  1  may be selected randomly by the mobile device  1  or by a user of the mobile device  1 . Alternatively, the set of identification data items may be selected by the server  2  and sent as a request to the mobile device  1 . Alternatively, the set of identification data items may be agreed between the server  2  and the mobile device  1  in a handshake operation in which it is determined which data items can be provided. For example, it will be appreciated that different devices (e.g., tablets and mobile telephones) may have different features which limit or facilitate the generation of one or more identification data items. 
     Having generated the identification data items  25 , processing passes from step S 8  to step S 9  at which the identification data items  25  are encrypted to provide encrypted identification data items  26 . In the example embodiment shown in  FIG. 4 , the identification data items  25  are each encrypted using the public key  16  of the server  2 . It is to be appreciated, however, that the identification data items may be encrypted using any appropriate encryption scheme, or transmitted in any appropriately secure manner. For example, the pre-shared token may be used as a symmetric encryption key, and the identification data items may be encrypted using the pre-shared token. In other embodiments, the identification data items  25  may not be encrypted before transmission to the server  2 . 
     The encrypted identification data items  26  are transmitted from the mobile device  1  to the server  2 . At step S 10 , the server  2  receives the encrypted identification data items  26  and, together with the private key  18 , the server  2  decrypts the encrypted identification data items  26  to obtain the data items  25 . 
     With reference to  FIGS. 5 and 6 , there is now described processing performed at the mobile device  1  for obtaining and transmitting evidential data to the server  2 . 
     At step S 15 , the mobile device  1  obtains data  35  which is to be used for the purpose of evidence. The data  35  may comprise a plurality of data items. For example, the data  35  may comprise one or more still images obtained using the camera  1   f  of the mobile device  1 , one or more videos captured using the camera  1   f , one or more sound records obtained with the microphone  1   g , etc. Where the data  35  comprises one or more video recordings, one or more of the video recordings may be separated into respective frames. 
     Processing passes to step S 16  at which a first data item from the data  35  is selected. At step S 17 , the data item is combined with the token  21  in order to generate a modified data item  36 . The token  21  may be combined with the data item in any appropriate way, such as, for example, prepending, appending, or distributing the token throughout the data item according to a predetermined scheme known to both the mobile device  1  and the server  2 . Processing passes from step S 17  to step S 18  at which a hash value  37  is generated based upon the modified data item  36 . The hash value  37  maybe generated using any appropriate hashing algorithm. As examples only, the widely used SHA1 or SHA2 hashing algorithm, or the newer SHA3 algorithm, may be used. 
     Processing passes from step S 18  to step S 19  at which it is determined whether there are any further data items in the data  35 . If it is determined that there are further data items, processing passes from step S 19  to step S 20  at which the next data item is selected. Processing passes from step S 20  to step S 17 . Processing therefore loops between steps S 17  to S 20  until each of the data items in the data  35  has been processed so as to generate a plurality of respective modified data items  36  and a corresponding plurality of hash values  37 . 
     When it is determined at step S 19  that all data items in the data  35  have been processed, processing passes to step S 21 , at which a single hash value  38  is generated from a bundle comprising each data item in the data  35 . The data bundle may further comprise the hash values  37 . The hash value  38  may be additionally or alternatively be generated from the data  35  combined in some, known way, with the token  21 . 
     At step S 22 , the data  35 , together with the hash values  37  and the hash value  38  is transmitted to the server  2 . By transmitting each of the hash values  37 , together with the hash value  38 , the server  2  is able to perform an initial check (based on the hash value  38 ) that the data  35  has not been modified. In particular, upon receipt of the data  35 , the server  2  is able to calculate a hash value that should have the same value as the hash value  38 . If it is discovered that the data has been modified or corrupted (because the hash value calculated by the server  2  does not match the hash value  38 ), because each of the hash values  37  are also transmitted, it is possible for the server  2  to subsequently identify exactly which of the data items in the data  35  has been modified, corrupted, or not transmitted by the mobile device  1 . 
     Additionally, one or more identifiers  25 ′ may be transmitted along with the evidential data at step S 22 . The identifiers  25 ′ may be referred to as transaction identifiers (as they are transmitted during a transaction) to distinguish them from the identifiers  25  which may be referred to as initialization identifiers (as they are transmitted during an initialization procedure). 
     The identifiers  25 ′ may comprise one or more of the same identifiers  25  that are transmitted to the server  2  at step S 10  of  FIG. 3 . For example, the server  2  may request, during a transaction, one or more specific identifiers (such as the IMEI number of the mobile device  1 ), or may request that identifiers corresponding to each of the identifiers  25  are included in the identifiers  25 ′. As described above, that while the identifiers  25 ′ may include one or more of the same type of identifier included in the identifiers  25  (e.g., “date” type identifiers), it is to be expected that the value of one or more of the identifiers may differ between the identifiers  25  and the identifiers  25 ′. As described above, the identifiers which are expected to differ may be referred to as variable identifiers. 
     Like the data items in the data  35 , each of the identifiers  25 ′ may additionally be combined with the token  21  and hash values calculated therefrom in order to create a bundle of identifier hash values  39 , which may be transmitted to the server  2 . In some embodiments, one or more of the hash values  39  are transmitted in place of the corresponding identifier  25 ′. For example, where the identifier  25 ′ is a static identifier (such as an IMEI number, which may be expected to be the same as it was when the corresponding identifier  25  was sent), a hash  39  of the static identifier may be transmitted to the server  2 , in place of re-sending the identifier. Where the static identifier is first modified using the token  21 , further checks may be performed by the server  2  to improve confidence that the device transmitting the identifiers  25 ′ is the mobile device  1 . 
     The processing of  FIG. 5  is such that when the data  35  is used as evidence, which may be after a period of storage at the server  2 , the server  2  can determine that the data  35  has not been tampered with or otherwise corrupted (i.e., that the data  35  is suitable for evidential uses). In particular, as now described with reference to  FIG. 7 , only the server  2  is able to re-create the hash values  37 ,  38  based on the received data. That is, as only the server  2  knows the value of the token  21  (and the scheme used to combine the token  21  with the data items of the data  35 ), only the server is able to re-create the hash values. As such, successful re-creation of the hash values  37 ,  38  at the server  2  is evidence that the data items are authentic and unmodified. Further, the identifiers  25 ′ and/or the identifier hash values  39  may be used to further confirm the identity of the mobile device  1 . 
     In addition to, or as an alternative to, being transmitted to the server  2 , the hash values  37 ,  38 ,  39  may be transmitted to an independent third party for secure storage until such a time as verification of the data  35  is required. Where both the server  2  and a third party receive the hash values  37 ,  38 ,  39 , verification of the data  35  may be performed by both the server  2  and an independent third party. In an embodiment, some or all of the hash values  37 ,  38 ,  39  are sent only to the third party. In some embodiments, the server transmits token  21  to a third party which may be the same or a different third party to that which receives the hash values  37 ,  38 ,  39 . It can be seen therefore, that independent verification of the data  35  may be provided by use of third parties unrelated to either the user of the mobile device  1  or the entity associated with the server  2 . 
       FIG. 7  illustrates processing that may be carried out at the server  2  upon receipt of evidential data from the mobile device  1  through the processing of  FIG. 6 . It will be appreciated the processing of  FIG. 7 , or similar processing may be carried out any stage after receipt of the data from the mobile device  1 . For example, the processing of  FIG. 7  (or similar) may be deferred until the data is to be used in an evidential fashion. For example, in the example above of vehicle insurance, processing to determine the veracity, authenticity, and trustworthiness of data received from the mobile device  1  may be deferred until a particular claim is processed by an agent of the insurer, for example. 
     Referring to  FIG. 7 , at step S 30 , data sent by the mobile device  1  is received at the server  2 . As described above, the data transmitted by the mobile device  1  comprises the data that is to be used as evidence, together with a plurality of hash values  37  (a respective hash value for each data item) and a single hash value  38  representing the data as a bundle (which may or may not be combined with the token  21 ). Processing passes from step S 30  to step S 31  at which the server  2  calculates at least one hash value based upon the received data and the token  21  stored at the server  2 . 
     In particular, the server  2  may first calculate only the hash value  38 . Respective hash values for each of the received data items may be calculated only in the event that the hash value  38  cannot be recreated by the server  2  in order to determine which data items are suspect. In other embodiments, the server  2  may calculate all of the hash values at the outset. 
     After calculating the hash values, processing passes to step S 32  at which the hash values calculated by the server  2  are compared with the hash values received from the mobile device  1 . If it is determined at step S 32  that the hash values calculated by the server  2  do not match the hash values received from the mobile device  1 , this indicates that the received data may have, for example, been modified, been corrupted during transmission, or originated from a device other than the mobile device  1  (such that the other device did not know the value of the pre-shared token  21 ). Where the hash values do not match, this may indicate that the data received at the server  2  is not suitable for use as evidence. Processing passes from step S 32  to step S 33 . 
     At step S 33 , an indication is provided (for example, an indication may be output to the display  2   e  of the server  2 , output to the display  1   e  mobile device  1 , and/or saved together with the received data at the server  2 ) that the calculated hash values do not match the received hash values. It will be appreciated that additional processing may be performed upon determination at step S 32  that the hash values do not match. For example, the received data may be rejected, and a message may be sent from the server  2  to the mobile device  1  requesting that the data be re-transmitted. Other processing that may be performed will be readily apparent to the skilled person. 
     If, on the other hand, it is determined at step S 32  that the hash values calculated by the server  2  do match the hash values received from the mobile device  1 , processing passes from step S 32  to step S 34  at which it is determined whether the one or more of the identifiers  25 ′ match the identifiers  25  that were sent from the mobile device  1  to the server  2  during the processing of  FIG. 3  and/or whether the identifier hash values  39  match corresponding hash values calculated by the server  2  based upon the identifiers  25  received during the processing of  FIG. 3 . It is to be understood that not all of the identifiers are necessarily checked at step S 34 . 
     If it is determined at step S 34  that the examined one or more identifiers  25 ′ do not match the corresponding identifiers  25  and/or that the identifier hash values  39  do not match corresponding hash values calculated by the server  2  based upon the identifiers  25 , processing passes from step S 34  to step S 35 , at which indication is provided (for example, an indication may be output on the server  2 , output on the mobile device  1 , or saved together with the received data) that the identifiers  25  do not match the identifiers  25 ′ and/or that the calculated hash values do not match the received hash values  39 . It will be appreciated that additional processing may be performed at step S 35 . For example, the data may be rejected, and a message may be sent from the server  2  to the mobile device  1  requesting that the data be re-transmitted. Other processing that may be performed will be readily apparent to the skilled person. 
     If, on the other hand, it is determined at step S 34  that the received identifiers  25 ′ do match the stored identifiers  25 , and/or that the received hash values  39  do match the calculated hash values, processing passes to step S 36 , at which the received data is stored for later use. Storage of the data may be, for example, on both the storage device  4  and the storage device  5 . Data stored on the storage device  4  may be accessible (for example, for viewing, annotating, modification, etc.) by the mobile device  1 , while data stored at the storage device  5  may be inaccessible to the mobile device  1 . In this way, data stored at the storage device  5  may be used to confirm that data stored at the mobile device  4  has not been modified in such a way that it can no longer be used for evidential purposes. 
     After each receipt of data, a new token may be exchanged between the server  2  and the mobile device  1  at step S 35 . As described above with reference to the processing of  FIG. 3 , a new token may be generated and exchanged in any appropriate way. For example, a new token may be selected randomly by one of the server  2  or the mobile device  1  and transmitted to the other device using public key cryptography. Alternatively, the server  2  may be issue a new token to the mobile device  1 , which the mobile device  1  salts with information known only to the mobile device  1  and the server  2  (such as one of the identifiers  25 ,  25 ′, a transaction number, etc.) 
     It will be appreciated, that even in the event that the data  35  is identified as originating from the mobile device  1 , and has not been modified or corrupted before receipt at the server  2 , it may be further desired to determine that the data  35  is trustworthy (i.e., that the user of the mobile device  1  has not fabricated the data  35 ). As will be described in more detail below, the identifiers  25 ′ may additionally be used to provide indications as to whether the data  35  is trustworthy. 
     After receiving data from the mobile device  1  during a transaction, the server  2  may perform background processing to compare the identifiers  25  with the identifiers  25 ′ to determine if the identifiers  25 ′ are valid or plausible in light of the identifiers  25 . For example, where the identifiers  25  and  25 ′ each include one or more time-based identifiers (such as a current time or date), it may be determined whether the time-based identifiers in the identifiers  25  precede the time-based identifiers in the identifiers  25 ′. As a further example, where the identifiers  25 ,  25 ′ each include a location based identifier (such as a GPS location, a current cell location, etc.) it may be determined whether it is feasible that the mobile device  1  could have reached the location indicated in the identifiers  25 ′ given the location indicated in the identifiers  25 . Determining whether a location is feasible may comprise comparing a distance between locations identified in each of the identifiers  25 ,  25 ′ with respect to a time indication. As a further example, where the identifiers  25 ,  25 ′ include hardware identifiers of the mobile device  1  (for example, battery serial number, IMEI number, phone uptime, last reboot, start time, etc.), comparisons may be made to identify inconsistencies. 
     It will be appreciated that a plurality of consistency checks may be performed based upon the identifiers  25 ,  25 ′. It will further be appreciated that in many cases, the data received at the server  2  may be accepted for storage even in the event of inconsistencies in the identifiers  25 ,  25 ′, where inconsistencies are merely noted along with the received data so that identified inconsistencies can be taken into account when assessing whether the received data is suitable for use as evidence. In other embodiments, however, determined inconsistencies may be used to automatically reject received data and/or trigger other processing such as requests for additional information. 
     It is described above that the initialization process comprises the exchange of identifiers which are utilized for comparison in further transactions. In other embodiments, initialization does not comprise the transfer of such identifiers. In some embodiments, identifiers may be transferred during each transaction and compared across different transactions. 
     In some embodiments, identifiers are transferred outside of transactions or initialization procedures, such that the server  2  maintains a regularly updated copy of relevant identifiers. For example, an application operating on the mobile device  1  may be arranged to transfer one or more identifiers to the server  2  in background processing operations. Alternatively, the application may prompt a user of the mobile device  1  to authorize transmission of identifiers outside of transactions initiated by the user. Such prompts or background processing operations may be at regular or random intervals. 
     It will be appreciated that aspects can be implemented in any convenient way, including by way of suitable hardware and/or software. For example, devices arranged to implement embodiments may be created using appropriate hardware components. Alternatively, a programmable device may be programmed to implement embodiments. 
     The invention therefore also provides suitable computer programs for implementing aspects. Such computer programs can be carried on suitable carrier media including non-transitory carrier media (e.g., hard disks, CD ROMs, and so on). 
     It will further be appreciated that while example embodiments are described above, modifications may be made to those examples without departing from the scope of the appended claims.