Unpredictable number generation

Abstract

A method of generating an unpredictable number in a computing device is provided. The method comprises the computing device performing the following programmed steps: obtaining a plurality of data elements; performing a first one way function on an internal value P and the plurality of data elements to update the value P; and performing a second one way function on the value P to obtain the unpredictable number. A computing device adapted to perform this method is also described.

1 . A method of generating an unpredictable number in a computing device, the method comprising the computing device performing the following programmed steps:
 obtaining a plurality of data elements;   performing a first one way function on an internal value P and the plurality of data elements to update the value P; and   performing a second one way function on the value P to obtain the unpredictable number.   
     
     
         2 . A method as claimed in  claim 1 , wherein at least one of the data elements varies with time or with activity of the computing device. 
     
     
         3 . A method as claimed in  claim 2 , wherein at least one of the data elements is a clock internal to the computing device. 
     
     
         4 . A method as claimed in  claim 1 , wherein at least one of the plurality of data elements is a random number generated internally to the computing device, the method further comprising generating the random number prior to performing the first one way function. 
     
     
         5 . A method as claimed in  claim 4 , wherein generating the random number comprises operating a hardware random number generator internal to the computing device. 
     
     
         6 . A method as claimed in  claim 1 , wherein one or both of the one-way functions are cryptographically secure one-way functions. 
     
     
         7 . A method as claimed in  claim 6 , wherein each cryptographically secure one-way function is a symmetric cipher, an asymmetric cipher, or a hash function. 
     
     
         8 . A method as claimed in  claim 1 , wherein the first one-way function and second one-way function are substantially the same. 
     
     
         9 . A method as claimed in  claim 1 , further comprising an initial step of obtaining a seeded value of P, and in obtaining an initial value of the unpredictable number by performing the first one way function on the seeded value of the value P and a plurality of startup data elements to update the value P;
 performing the second one way function on the value P to obtain the unpredictable number.   
     
     
         10 . A method of authenticating a transaction between computing devices at a first computing device, comprising:
 generating an unpredictable number at the first computing device based on application of a first and a second one way function on a plurality of data elements;   transmitting the unpredictable number and transaction data to a second computing device;   receiving, from the second computing device, cryptographically signed data formed from at least some of the transaction data and the unpredictable number; and   reviewing the cryptographically signed data to determine that it incorporates the unpredictable number.   
     
     
         11 . A method as claimed in  claim 10 , wherein at least one of the plurality of data elements is transaction dependent. 
     
     
         12 . A method as claimed in  claim 11 , wherein one or more of the transaction dependent data elements is an identity associated with one of the two computing devices. 
     
     
         13 . A method as claimed in  claim 10 , wherein the transaction is a financial transaction, wherein the first computing device is a terminal and wherein the second computing device is at least one of (i) a transaction card and (ii) a proxy for a transaction card. 
     
     
         14 . A method as claimed in  claim 13 , wherein one of the transaction related data elements is a financial value associated with the transaction. 
     
     
         15 . A computing device comprising;
 a memory storing processor-executable program code; and   a processor to execute the processor-executable program code in order to cause the computing device to:
 obtain a plurality of data elements; 
 perform a first one way function on an internal value P and the plurality of data elements to update the value P; and 
 perform a second one way function on the value P to obtain the unpredictable number. 
   
     
     
         16 . A computing device as claimed in  claim 15 , further comprising a hardware random number generator. 
     
     
         17 . A computing device as claimed in  claim 15 , wherein the processor further executes program code to cause the computing device to authenticate a transaction with a second computing device, where the program code further comprises code to:
 transmit the unpredictable number and transaction data to the second computing device;   receive, from the second computing device, cryptographically signed data formed from at least some of the transaction data and the unpredictable number; and   review the cryptographically signed data to determine that it incorporates the unpredictable number.   
     
     
         18 . A computing device as claimed in  claim 17 , wherein the computing device is adapted to make a data connection with the second computing device. 
     
     
         19 . A computing device as claimed in  claim 17 , wherein the computing device is a point of interaction or is able to make a data connection with a point of interaction and the second computing device is payment device. 
     
     
         20 . A computing device as claimed in  claim 17 , wherein the point of interaction is a point of sale terminal. 
     
     
         21 . A computing device as claimed in  claim 17 , wherein the point of interaction is an automatic teller machine.