SCRAMBLE: The State, Connectivity and Routing Augmentation Model for Building Logic Encryption
This addresses hardware security for integrated circuits by protecting against reverse engineering and tampering, though it appears incremental as it builds on existing logic locking methods.
The paper tackles the problem of securing sequential circuits against attacks by introducing SCRAMBLE, a logic locking solution that hides state transitions, connectivity, and scan chains among key-controlled false elements, and demonstrates its resistance to 2-stage and SAT-based attacks with specific variants.
In this paper, we introduce SCRAMBLE, as a novel logic locking solution for sequential circuits while the access to the scan chain is restricted. The SCRAMBLE could be used to lock an FSM by hiding its state transition graph (STG) among a large number of key-controlled false transitions. Also, it could be used to lock sequential circuits (sequential datapath) by hiding the timing paths' connectivity among a large number of key-controlled false connections. Besides, the structure of SCRAMBLE allows us to engage this scheme as a new scan chain locking solution by hiding the correct scan chain sequence among a large number of the key-controlled false sequences. We demonstrate that the proposed scheme resists against both (1) the 2-stage attacks on FSM, and (2) SAT attacks integrated with unrolling as well as bounded-model-checking. We have discussed two variants of SCRAMBLE: (I) Connectivity SCRAMBLE (SCRAMBLE-C), and (b) Logic SCRAMBLE (SCRAMBLE-L). The SCRAMBLE-C relies on the SAT-hard and key-controlled modules that are built using near non-blocking logarithmic switching networks. The SCRAMBLE-L uses input multiplexing techniques to hide a part of the FSM in a memory. In the result section, we describe the effectiveness of each variant against state-of-the-art attacks.