Authentication method using physical unclonable functions

1. A method of authenticating a target device using a reader and a data store, the reader being configured to send a challenge data values to the target device, the target device being configured to generate a response data value in response to receiving said challenge data value, wherein the response data value sent by said target device is determined by one or more physical characteristics of the target device that result from manufacturing of said target device, and wherein the data store comprises a plurality of challenge-response data sets, each challenge-response data set comprising a challenge data value and a plurality of corresponding response data values, the method comprising:

sending multiple times the respective challenge data value from a selected one of said plurality of challenge-response data sets from said reader to said target device;

receiving at said reader the respective response data value generated by said target device in response to each instance of said respective challenge data value sent by said reader;

determining a representative response data value from said response data values received by said reader in response to said instances of said respective challenge data value sent by said reader;

comparing said representative response data value against said response data values in said selected challenge-response data set; and

determining that said target device is authentic if said representative data value matches any one of said response data values from said selected challenge-response data set.

2. A method as claimed in claim 1 , further including determining said representative response data value as the response data value most commonly received by said reader in response to said instances of said respective challenge data value sent by said reader.

3. A method as claimed in claim 2 , further including, in a registration phase, sending each of a plurality of challenge data values to said target device multiple times; receiving at said reader the respective response data value generated by said target device in response to each instance of each challenge data value sent by said reader; and recording each challenge data value in association with the respective response data values in a respective one of said challenge-response data sets.

4. A method as claimed in claim 1 , wherein said target device comprises a physical unclonable function (PUF) device.

5. A method as claimed in claim 1 , further including generating at said target device a pseudo-random response data value in response to receiving said challenge data value.

6. A method as claimed in claim 1 , wherein a plurality of different selected challenge data values are each sent from said reader to said target device multiple times.

7. A method as claimed in claim 1 , further including, in an identification phase, sending an identification challenge data value to said target device; receiving at said reader an identification response data value generated by said target device in response to said identification challenge data value sent by said reader; comparing said identification response data value against a respective identification response data value associated with each challenge-response data set; and selecting the challenge-response data set associated with the identification response data value that matches said identification response data value generated by said target device.

8. A method as claimed in claim 7 , further including performing said identification phase before said authentication, and using said selected challenge-response data set in said authentication.

9. A method as claimed in claim 7 , further including sending said identification challenge data value to said target device multiple times.

10. A method as claimed in claim 3 , further including, during said registration phase, sending an identification challenge data value to said target device; receiving at said reader an identification response data value generated by said target device in response to said identification challenge data value sent by said reader; storing said identification response data value in association with a respective one of said challenge-response data sets associated with said target device.

11. A method as claimed in claim 1 , further including determining the number of times to send a challenge data value to said target device depending on the number of unstable bits in the response data value generated by the target device.

12. A reader for authenticating a target device using a data store, the reader being configured to send challenge data values to the target device, the target device being configured to generate a response data value in response to receiving said challenge data value, wherein the response data value sent by said target device is determined by one or more physical characteristics of the target device that result from the manufacturing of said target device, and wherein the data store comprises a plurality of challenge-response data sets, each challenge-response data set comprising a challenge data value and a plurality of corresponding response data values, the reader comprising means for sending multiple times the respective challenge data value from a selected one of said plurality of challenge-response data sets to said target device; means for receiving the respective response data value generated by said target device in response to each instance of said respective challenge data value sent by said reader; means for determining a representative response data value from the response data values received in response to said instances of said respective challenge data value sent by said reader; means for comparing said representative response data value against said response data values in said selected challenge-response data set; and means for determining that said target device is authentic if said representative data value matches any one of said response data values from said selected challenge-response data set.