How to Prove Work: With Time or Memory

Abstract

Proposed by Dwork and Naor (Crypto' 92) as an anti-spam technique, proof-of-work is attracting more attention with the boom of cryptocurrencies. A proof-of-work scheme involves two types of participants, i .e., provers and verifiers. Provers are asked to solve a computational puzzle, and verifiers need to check the solution's correctness. A widely adopted hash-based construction achieves an optimal gap in computational complexity between provers and verifiers. However, in industry, proof-of-work is done by highly dedicated hardware, e.g., "ASIC", which is not generally accessible, let alone the high energy consumption rates. In this work, we turn our eyes back to the original meaning of "proof of work". Under a trusted setting, we propose a framework and its constructions based on computationally hard problems and the unified definition of hard cryptographic primitives by Biryukov and Perrin (Asiacrypt' 17). The new framework enables us to have a proof-of-work scheme with time-hardness or memory-hardness while cutting down power consumption and reducing the impact of dedicated hardware.INDEX TERMS Blockchain, moderate hard primitives, proof-of-work.