Rebuttal to “Comments on ‘A PUF-FSM Binding Scheme for FPGA IP Protection and Pay-Per-Device Licensing”’

Concerns have been raised about our recently published article on a PUF-FSM binding scheme for FPGA IP protection and Pay-per-Device licensing. In a comment, the authors first analyzed the simple 4-bit license example we used in the article and claimed that the low overhead configuration of the FSM binding does not provide sufficiently high level of security. Then they analyzed the FSM binding structure and claimed that when a 128-bit long license is used to provide high security, the PUF-FSM scheme will incur unacceptable overhead. Both the analyses seem correct. However, they focus on some illustrative examples of our proposed binding scheme, not the main contribution which is a non-encryption based binding mechanism and its application to FPGA IP protection and pay-per-device licensing. The first claim on the low security of the 4-bit license example is true, but it is just a simple example, in reality, the key/license will be much longer. For the second claim, the balance of overhead and security can be addressed by some simple tricks such as adding few black holes used in FSM binding and the augment of number of inputs of STG. In this rebuttal, we will elaborate these.