FROG: Forward-Secure Post-Quantum Signature

Forward-secure signatures guarantee that the signatures generated before the compromise of private key remain secure, and therefore offer an enhanced compromise-resiliency for real-life applications such as digital forensics, audit logs, and financial systems. However, the vast majority of state-of-the-art forward-secure signatures rely on conventional intractability assumptions and therefore are not secure against quantum computers. Hash-based signatures (HBS) (e.g., XMSS) can offer forward-secure post-quantum security. However, they are efficient only for a pre-defined number of messages to be signed and incur high key generation overhead, highly expensive signing, and large signature sizes for an increasing number of messages. It is an open problem to develop quantum-safe forward-secure signatures that are efficient and practical with a signing capability scalable to their security parameters. In this work, we propose a new series of post-quantum signatures that we call FROG (Forward-secuRe pOst-quantum siGnature). Unlike HBS alternatives, FROG can achieve highly computational efficient signatures with sub-linear key/signature sizes and (practically) unbounded signing capability. This is achieved by transforming suitable post-quantum signatures into forward-secure settings via MMM constructions. We investigated the transformation of prominent post-quantum secure signatures such as Dilithium, WOTS, and BLISS with MMM. Our experiments indicate that FROG outperforms XMSS for the vast majority (if not all for a large number of messages) of performance metrics. We also discuss one-time variants of these base signature schemes that can push the performance of FROG to the edge. Overall, FROG shows a better performance than the existing alternatives with forward-security and therefore is an ideal alternative for the standardization efforts for forward-secure post-quantum signatures.