Bilateral-secure Signature by Key Evolving

In practice, the greatest threat against the security of a digital signature scheme is the exposure of signing key, since the forward security of past signatures and the backward security of future signatures could be compromised. There are some attempts in the literature, addressing forward-secure signature for preventing forgeries of signatures in the past time; however, few studies addressed the backward-security of signatures, which prevents forgeries in the future time. In this paper, we introduce the concept of key-evolving signature with bilateral security, i.e., both forward security and backward security. We first define the bilateral security formally for preventing the adversaries from forging a valid signature of the past and the future time periods in the case of key exposure. We then provide a novel construction based on hub-and-spoke updating structure and the random oracle model, and show that the construction achieves bilateral security and unbounded number of time periods. Finally, we compare our scheme with the existing work by rigorous analysis and experimental evaluation, and demonstrate that our construction is more secure and efficient for practical applications.