An overclocking clock software PUF circuit with no additional hardware resource overhead based on video coding circuit

—Physical unclonable function (PUF) as an emerging hardware security primitive has caused extensive research by scholars. PUF extracts unclonable fingerprint information from intrinsic changes in the circuit during operation. However, conventional PUFs usually adopt the dedicated circuit structure to generate random, non-clonable responses, which require additional hardware resource overhead. This article proposes a software PUF (SPUF) based on the video encoding circuit in response to the above issues. SPUF causes abnormal operation of the encoding circuit by applying an overclocking clock. A response key with circuit characteristics is generated by exploiting the response to timing path dependence. Primarily, the video coding circuit, which is part of the open-source H265 IP Core, is taken as the PUF circuit carrier. Secondly, after analyzing the timing path of the encoding circuit, an overclocking signal is selected according to the timing path to put the circuit in abnormal operating mode. Then, unclonable random data is generated while completing video encoding and compression. Next, the response data is obfuscated by gray encoding and XOR operation to improve the responses' reliability further. Finally, a both-way encrypted lightweight authentication protocol is constructed. Encrypting the video stream with SPUF responses and random numbers enables bi-directional encrypted transmission between the device and the server. The test results show that the proposed SPUF passes the NIST test with a uniqueness of 48.87 %. The autocorrelation coefficient is 0.0204 at 95 % confidence, showing good randomness and uniqueness.