SCRAMBLE: The State, Connectivity and Routing Augmentation Model for Building Logic Encryption

TL;DR

SCRAMBLE is a novel logic locking scheme for sequential circuits that secures FSMs, timing paths, and scan chains by hiding critical information among many false connections, resisting advanced attack methods.

Contribution

Introduces SCRAMBLE, a new logic locking approach with two variants, enhancing security of sequential circuits against sophisticated attacks.

Findings

SCRAMBLE effectively resists 2-stage FSM attacks.

SCRAMBLE variants withstand SAT-based and model checking attacks.

The scheme improves security without significant performance overhead.

Abstract

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.