Abstract:
A method for generating a data transaction ID for an interaction between first and second units, the method comprising: the first data unit generating a first data item as a function of a first time data element, the first time data element being representative of a first time value, and transmitting the first data item to the second data unit; the second data unit generating a second data item as a function of the received first data item and transmitting the second data item to the first data unit; and the first data unit generating a third data item as a function of the second data item and a second time data element, the second time data element being representative of a second time value, wherein the third data item comprises a transaction ID unique to the interaction between the first and second data units.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from co-pending United Kingdom utility application entitled, “Method and System for generating data transaction ID” having serial no. GB 0621521.4, filed Oct. 30, 2006, which is entirely incorporated herein by reference. 
     BACKGROUND 
     As RFID tags become increasingly ubiquitous in their use in conjunction with the growing range of applications, it is increasingly common for such RFID tags to be used to record a data transaction event between the RFID tag and an appropriate read/write device. By recording the data transaction events a data log of the transactions that includes, amongst other data items, the dates and times of the data transactions can be created that can be used as evidence of the completion of the data transactions. Examples of uses of RFID tags in this manner may involve a portable read/write device being used to complete data transactions between multiple RFID tags, each of which are fixed to separate items, the read/write device maintaining a data log of those items that have been physically visited by the read/write operator such that it can be later verified that all necessary items have been physically visited. For example, this arrangement may be used to verify that all fire extinguishers equipped with an RFID tag have been physically examined by a fire safety officer equipped with a suitable read/write device, alternatively a similar arrangement could be used to verify that a service engineer has physically visited (and thus presumably checked) the appropriate RFID tag equipped machinery, the data log providing the basis for proof of completion of paid for service tasks. In these latter examples, it is advantageous for the read/write device operator not to be able to falsify the data transaction between the read/write device and the respective RFID tags so as to prevent fraudulent work claims being made. For example, it is desirable that it is not possible to falsify the date and/or times at which a data transaction between the read/write device and an RFID tag has been made. 
     OVERVIEW 
     According to a first aspect of the present invention there is provided a method for generating a data transaction ID for an interaction between a first and a second data unit, the method comprising the first data unit generating a first data item as a function of a first time data element, the first time data element being representative of a first time value, and transmitting the first data item to the second data unit, the second data unit generating a second data item as a function of the received first data item and transmitting the second data item to the first data unit and the first data unit generating a third data item as a function of the second data item and a second time data element, the second time data element being representative of a second time value, wherein the third data item comprises a data transaction ID unique to the interaction between the first and second data units. 
     The generation of the first and third data item may also a function of a first secret data value associated with the first data unit and the generation of the second data item may also be a function of a second secret data value associated with the second data unit. Consequently the method may further comprise generating the first data item by combining the first time data element and the first secret data value and performing a hashing operation on said combination, generating the second data item by performing a hashing operation on a combination of the first data item and the second secret data value and generating the third data by combining the second data item, the second time data element and the first secret data value and performing a hashing operation on said combination. 
     The first and second time data elements may be generated according to a pseudo-random number series having a one-to-one correspondence to an actual time. In other words, for a given real time and with knowledge of the pseudo-random number series it is possible to calculate the corresponding pseudo-random number. 
     The method may further comprise associating a first data unit identification code, a second data unit identification code and first and second real time values with the generated data transaction ID. 
     According to a further aspect of the present invention there is provided a method of validating a data transaction ID generated according to the previously mentioned aspect of the invention comprising determining the first and second time data elements corresponding to the associated first and second real time values generating a validation transaction ID by performing a sequence of hashing operations on one or more of the determined first and second time data elements and the first and second secret data values associated to the first and second data unit identification codes respectively, the sequence of hashing operations being identical to those performed to generate the data transaction ID and validating the data transaction ID only if it is equal to the validation transaction ID. 
     Preferably, prior to generating the validation transaction ID the difference between the first and second real time values may be determined and if the difference is greater than a predetermined time value the data transaction ID is deemed invalid. 
     According to another aspect of the present invention there is provided a system for generating a data transaction ID comprising first and second data processors, the first data processor being arranged to generate a first time data element representative of a first time value, generate a first data item as a function of the first time data element and transmit the first data item to the second data processor, the second data processor being arranged to generate a second data item as a function of the first data item and transmit the second data item to the first data processor, the first data processor being further arranged in response to receiving the second data item to generate a second time data element representative of a second time value and generate a third data item as a function of the second time data element and the second data item. 
     The first data processor may comprise data storage having a first secret data value stored therein and the first and third data item is generated as a function of said first secret data value and wherein the second data processor comprises data storage having a second secret data value stored therein and the second data item is generated as a function of said second secret data value. 
     Additionally, the first data processor may be arranged to generate the first data item by combining the first time data element and the first secret data value and perform a hashing operation on the resultant combined value and is further arranged to generate the third data item by combining the second data item, the second time data element and the first secret data value and performing a hashing operation on the resultant combined value, and wherein the second data processor is arranged to generate the second data item by combining the first data item and the second secret data value and performing a hashing operation on the resultant combined value. The combining operation may comprise any one or more of concatenation, XOR-ing and AND-ing. 
     The first data processor may be arranged to generate said time data elements according to a predetermined pseudo-random number sequence. 
     The first and second data processors preferably comprise physically separate devices. Preferably the second data processor comprises an RFID tag and the first data processor comprises an RFID tag read/write device. 
     According to a further aspect of the present invention there is provided a system for validating a data transaction ID generated by the previously mentioned system, the system comprising a validation data processor arranged to receive from the first data processor a data transaction ID, first and second time values associated with the data transaction ID and first and second data processor identification codes and arranged to generate first and second time data elements corresponding to the received first and second time values, generate a validation transaction ID by performing a sequence of transformations on one or more of the first and second time data elements and the first and second secret data values associated to the first and second data processor identification codes, the sequence of transformations being identical to those performed to generate the data transaction ID and validate the received data transaction ID only if it is equal to the validation transaction ID. 
     The validation processor may be arranged to determine the difference between the received first and second time values prior to generating the validation transaction ID and if the difference is greater than a predetermined time value to declare the data transaction ID invalid. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments of the present invention will now be described, by way of illustrative example only, with reference to the accompanying figures, of which: 
         FIG. 1  schematically illustrates the components of a read/write device and an memory tag suitable for use in embodiments of the present invention; 
         FIG. 2  schematically illustrates an implementation of the memory tag and reader/writer illustrated in  FIG. 1 ; 
         FIG. 3  schematically illustrates the generation of a transaction ID according to an embodiment of the present invention; and 
         FIG. 4  schematically illustrates the method of validating a data transaction ID according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates first and second data units  2 ,  4  between which a data transaction may occur. The first data unit  2  includes a read/write apparatus  6  according to an embodiment of the present invention. The read/write apparatus includes an input/output interface  8 , a first data processor  10 , a clock  12 , a random time generator  14  and a memory module  16 , all of which are connected to one another by means of an appropriate data bus  18 . The memory module  16  has a read/write data item stored therein that uniquely identifies the read/write device within the first data unit and in the embodiment illustrated also has a first “secret” S 1  stored therein, the first secret S 1  may comprise another unique number of code. The memory module  16  also includes capacity for general data storage. 
     The second data unit  4  includes an memory tag  20 , such as a “memory spot” for example, which is a proprietary RFID tag manufactured by the current applicant. The memory tag includes a second input/output interface  22 , a second data processor  24  and a second memory module  26 , all of which are connected to each other via second data bus  28 . The second memory module  26  has a unique memory spot identification code stored therein, together with a second “secret” S 2  and general data storage means. 
     Referring now to  FIG. 2 , an example of the possible circuitry  220  of a memory tag  4  and exemplary circuitry of the I/O interface  8  of a read/write device  6  (not shown) are illustrated schematically, using conventional component identifications (C-capacitor, L-inductance, R-resistor, D-diode and S-switch). In an embodiment, the input/output interface  22  of the memory tag  14  comprises an RF transponder circuit including a capacitor C 2  which, in combination with an antenna coil L 2 , forms a resonant circuit with component values being chosen to tune the combination to a frequency of approximately 2.45 GHz (for example) for inductive coupling with the read/write device. The portion of transponder circuit responsible for power supply is diode D 1  and capacitor C 4 , with diode D 1  rectifying the alternating current generated by the inductive coupling and the capacitor C 4  acting as a power supply storage. The portion of the transponder circuit responsible for receiving transmitted data from the read/write device is diode D 2 , capacitor C 5  and resistor R 1  which form a simple envelope detector. The data thus received is stored in memory  26 . The portion of the transponder circuit responsible for the reading of data from the memory  26  is the tuned circuit L 2 /C 2  in combination with S 1  and C 3 . Switching C 3  in and out of the circuit using S 1  changes the resonance of tuned circuit L 2 /C 2  resulting in phase modulation of the reflected power from the memory tag  14  to a read/write device. 
     An example of the implementation of the first and second data units  2 ,  4  is the first data unit  2  comprising a handheld computing device, such as a PDA or laptop computer, and the second data unit  4  comprising a computer printer. The handheld read/write device is thus likely to be used by a service engineer who is tasked with inspecting and/or servicing one or more computer printers, as represented by the second data unit  4 . To confirm that a particular printer has been serviced a data transaction occurs between the read/write device (first data unit  2 ) and the memory tag  20  located on the printer (second data unit  4 ). In the illustrated embodiment in  FIG. 1  the necessary data communication goes between the first and second input/output units  8 ,  22  and will occur by means of inductive coupling. However, it will be appreciated that other wireless transmission techniques may be employed and in some embodiments non-wireless communication may be utilised. 
     Prior to being issued to an operator, the read/write device  6  must first be initialised by the third party issuing the read/write device to the end user. In the example previously given, the third party issuing the read/write device would be the party responsible for making payment to the service engineer for performing the service checks on the computer printers. So the third party could be the engineers employer or alternatively the owner of the computer printers that will be making payments on the basis of a service contract with the service engineer. The initialisation process involves loading the read/write ID and the first secret S 1  onto the memory module  16  of the read/write device. The initialisation process also involves initialising the random time generator  14 . This is accomplished by recording the real time at which the random time generator is initialised. The random time generator generates a series of pseudo-random numbers, which may or may not be in an accepted time format, at discrete time intervals. The means by which the pseudo-random numbers are generated preferably utilises cryptographic algorithms that render it extremely difficult to determine the actual order of the pseudo-random number series or to generate a false pseudo-random number. The pseudo-random number series preferably has a one-to-one correspondence to an actual time. In other words, for a given real time and with knowledge of the pseudo-random number series it is possible to calculate the corresponding pseudo-random number. The read/write device ID, the first secret S 1  and the actual time at which the random time generator was initialised are all recorded and maintained in a secure database by the initialising third party. 
       FIG. 3  schematically illustrates a process and data flow for generating a transaction ID for a data transaction between the read/write device and the memory spot illustrated in  FIG. 1 . The left hand side of  FIG. 3  illustrates the data flows and processing steps that occur in the read/write device  6 , whilst the right hand side of  FIG. 3  illustrates the data flows and processing steps that occur within the memory tag  20 . To generate a data transaction ID, T ID  a first hashing operation is performed on the first secret S 1  and a first random time value, RT 1  which is representative of a first time value. In the particular embodiment illustrated in  FIG. 3  the first random time value RT 1  is concatenated with the first secret S 1  and the resulting data word is then hashed in the first hashing operation to provide a hash output. The hashed output from the first hashing operation  30  is transmitted from the read/write device  6  to the memory tag  20 , where it is combined with the second secret S 2  that is stored in the memory module  26  of the memory tag and the combined data value is further hashed in a second hashing operation  32  to provide a second hash output. The second hashed output is transmitted from the memory tag to the read/write device, together with the unique memory tag identification code, MS ID . In the embodiment illustrated in  FIG. 3  the second hashed output is XORed with a second random time value RT 2 , which is representative of a second real time value. By XORing the second random time value and the second hashed output from the memory tag a data word is generated at step  34 , which is then concatenated with the first secret S 1  and the concatenated value is hashed again in a third hashing operation  36 . The result of the third hashing operation comprises the unique transaction ID, T ID  that is, for example, subsequently stored in the memory module  16  of the read/write device  6 , together with the memory tag identification code MS ID  and the real times t 1 , t 2  that correspond to the random time values RT 1  and RT 2 . The real time values t 1  and t 2  are either derived directly from the random time data values or are read in real time from the separately provided clock  12  included in the read/write device  6 . The read/write ID is also stored with the transaction ID. Since the process of generating the transaction ID utilises two separate time related values, each transaction ID will be unique to a particular data transaction. Furthermore, since each transaction ID is derived from two time elements and two secret values associated respectively with the memory tag and read/write device, the transaction ID proves that the specified read/write device was used on the specified memory tag at the specified time. 
     Once a transaction ID has been generated and recorded it may subsequently be validated by the third party that issued the read/write device. The method of validating a transaction ID is schematically illustrated into  FIG. 4 . The transaction ID T ID , read/write device ID RW ID , the memory tag identification MS ID  and the real time values used during the generation of the transaction ID are all provided from the memory of the read/write device. An initial step  38  is to calculate the difference between the second and first time values, since this is indicative of the time taken to generate the transaction ID. For the transaction to be valid the difference between the first and second real time values should be no greater than a predetermined maximum, for example 1-2 seconds, since the time taken for the transaction ID to be generated by the read/write device should be minimal. If the difference between the time values is greater than the predetermined maximum then this is indicative that the transaction ID was generated fraudulently and in fact was not generated during a real time data transaction between the read/write device and the memory tag. Consequently if the time difference is greater than the predetermined value the verification process is considered to be a fail. If the difference between the first and second to real time values is less than the predetermined maximum, and is thus acceptable, the pseudo-random time values corresponding to the real time values are generated, as illustrated at step  40 . This is possible since the real time at which the random time generator  14  of the particular read/write device identified by the read/write ID is known by the verifying body and thus the value of the pseudo-random time sequence corresponding to the respective real times recorded during the transaction process can be calculated. Having obtained the first and second random time values RT 1  and RT 2 , the sequence of hashing operations utilising these values and the first and second secrets S 1  and S 2 , which are also recorded by the verifying authority, can be repeated, as represented at stage  42  in  FIG. 4  the repetition of the hashing sequence thus independently generates a transaction ID value referred to as the verification transaction ID VT ID . This value is compared to the recorded transaction ID provided by the read/write device, step  44  and only if the two values are exactly the same, i.e. VT ID =T ID , is the transaction ID fully verified. Once the transaction has been verified a payment of the service operator, using the previous example, may be authorised. 
     The method and apparatus of generating and validating a data transaction ID according to the above described embodiments provides an extremely secure system for validating that certain claimed data transaction have indeed taken place. Examples of possible applications include warranty and/or service claims, where the person performing the service or warranty action cannot necessarily be trusted. In this instance a claim ID (data transaction ID) must be generated by the individual for every service/warranty action for which payment is requested. Therefore it is important that false claim IDs cannot be generated, even in the absence of access to a users central computer network, something embodiments of the present invention prevents by use of the time data elements. A further application is in the field of health care, where the data transaction ID can be used to provide a secure record that a particular drug has been administered to a patient or has been taken from a dispensary by a particular individual.