Hardware intrinsic security from D flip-flops

In this paper we describe the results of our investigations Supported by EU FP7 project UNIQUE on the randomness and reliability of D flip-flops when used as a Physically Unclonable Function (PUF). These D flip-flops are hardware components which present a random start-up value when powered up. We show that against all odds, enough randomness exists in such elements when implemented on an Application-Specific Integrated Circuit (ASIC) to turn the responses of a number of D flip-flops into a secret random sequence allowing to derive keys for use in conjunction with cryptographic algorithms. In addition to being unpredictable, these flip-flops have the advantage that they can be spread over random locations in an ASIC. This makes them very difficult to reverse-engineer when used to hide a secret key in a design at a relatively small cost in resources.