| CPC H04L 9/088 (2013.01) [H04L 9/3278 (2013.01)] | 17 Claims |

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1. A physically unclonable function (PUF) device comprising:
a plurality of optical fibres, at least some of which are arranged such that they are optically coupled;
a media surrounding at least a portion of the optical fibres;
at least one light source configured to transmit light through one or more of the optical fibres;
at least one light sensor configured to receive the transmitted light from one or more of the optical fibres and provide an output; and
circuitry for applying a challenge signal to at least one of the fibres using the at least one light source and for receiving the output from the at least one light sensor to generate an identifying response to the challenge signal, the fibres being arranged such that the identifying response is unique to the device, wherein
the circuitry for applying the challenge signal is arranged to vary the fibres to which the challenge signal is applied and/or the sensors from which the response is received after each challenge is applied to the device, and/or
the circuitry for applying the challenge signal is arranged to vary the number of fibres to which the challenge signal is applied and/or the number of sensors from which the response is received after each challenge is applied to the device.
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