TETRIS: Automated Design Space Exploration of Randomness-Latency Trade-offs in Masked Hardware

Abstract

Given a fixed security order, the randomness and latency of masked hardware present a trade-off. This trade-off has not been structurally examined well enough to enable an efficient search for a user-optimal (randomness/latency-efficient) masked design. Gadget-based masking simplifies masking by replacing each unmasked primitive circuit with a corresponding masked circuit, called a gadget, to realize a larger masked design. These gadgets, in turn, have masking-order-dependent latency-randomness costs, lending a structure to the randomness and latency of gadget-based masked hardware. This structure enables automated Design-Space Exploration (DSE) of gadget-based masked hardware that takes in a user’s constraints on randomness (or latency) to arrive at the latency (or randomness) optimal assignment of gadgets with less area and vice versa. This article introduces a software-level DSE approach, the basis of which is the two DSE algorithms - Minimize Latency under Randomness Constraints (MLRC) and Minimize Randomness under Latency Constraints (MRLC), which are duals of each other. While prior work optimizes masked hardware by formulating a global optimization based on the Boolean Satisfiability Problem (SAT), our results show that gadget-based masked hardware using Probe-Isolating Non-Interference (PINI) gadgets embodies a structured trade-off, enabling efficient heuristic-based solutions rather than relying on heavy global optimizations. This gives our tool comparable or superior area results in under a millisecond - a speedup of upto several orders of magnitude to the State-of-the-Art tools.