A hybrid watermarking scheme for sequential functions

Most watermarking schemes for intellectual property (IP) protection embed authorship information at a single design abstraction level. Effective means to directly verify the watermark distributed at the downstream designs are lacking, particularly after the IP core is packaged into chip. This paper proposes a hybrid scheme for watermarking sequential designs. At behavioral level, the finite state machine (FSM) is watermarked by interweaving the watermark bits into the outputs of its existing and unspecified transitions. During the Design-for-Testability (DfT) process, the scan chain that incorporates the watermarked FSM as one of the test kernels is further watermarked to provide a second level of protection. It enables the watermark on the FSM to be publicly detectable by the legitimate end users off chip via the scan test. Experimental results on ISCAS'89 and LGSynth'93 benchmark circuits show that the watermarked circuits have acceptably low overheads with stronger authorship proof.