Proof-of-Useful-Work: BlockChain Mining by Solving Real-Life Optimization Problems

Abstract

Blockchains (BCs) are distributed database systems, popular for their innovative, unsupervised maintenance process. They use a so-called consensus protocol to prevent inference by any third party of absolute trust. Security, privacy, consistency, and energy consumption have been identified as the main issues involved in BC maintenance. According to the recent literature, some of these issues can be formulated as combinatorial optimization (CO) problems, and this fact motivated us to consider incorporating CO approaches into a BC. In this paper, we propose the new combinatorial optimization consensus protocol (COCP) based on the proof-of-useful-work (PoUW) concept that assumes solving instances of real-life CO problems. Due to the complexity of the underlying CO problems, we have developed various types of heuristic methods, which are utilized in the COCP. Most of these methods are problem-dependent stochastic heuristic or metaheuristic methods. As is the case with the majority of consensus protocols, PoUW exhibits the property of asymmetry. It is difficult to find a solution for the considered CO problem; however, once a solution is found, its verification is straightforward. We present here a BC framework combining the two above-mentioned fields of research: BC and CO. This framework consists of improvements aiming towards developing the COCP of the PoUW type. The main advantage of this consensus protocol is the efficient utilization of computing resources (by exploring them for finding solutions of real-life CO problem instances), and the provision of a broad range of incentives for the various BC participants. We enumerate the potential benefits of the COCP with respect to its practical impacts and savings in power consumption, describing in detail an illustrative example based on part of the real-life BC network. In addition, we identify several challenges that should be resolved in order to implement a useful, secure, and efficient PoUW consensus protocol.

Controlling the Difficulty of Combinatorial Optimization Problems for Fair Proof-of-Useful-Work-Based Blockchain Consensus Protocol

“…The problem of controlling the difficulty of miners' work appears also in the PoUWbased consensus protocols [1][2][3][4][5], known in the literature as an energy efficient alternative to PoW. Some of the early attempts to implement PoUW-based consensus protocols involve [6][7][8].…”

“…In a most recent work in the literature [4], the authors also proposed a PoUW-based consensus protocol, named CO Consensus Protocol (COCP). The main advantage of COCP is the efficient utilization of computing resources by providing valid solutions for the reallife instances of any CO problem.…”

“…Regarding the control of mining difficulty, in [4] the authors considered three avenues. They put an emphasis on the COCP usefulness stating that for the clients both hard and easy instances are equally important.…”

“…Blockchain (BC) consensus protocols based on the Proof-of-Useful-Work (PoUW) paradigm [1][2][3][4] were developed to ensure the efficient exploration of resources. They capitalize on the effort of BC participants, called miners, who solve problems useful to some other participants or the community in general.…”

“…They capitalize on the effort of BC participants, called miners, who solve problems useful to some other participants or the community in general. For example, useful work considered in [1][2][3][4][5][6][7][8], consists of solving the real-life instances of some Combinatorial Optimization (CO) problems. At the same time, PoUW-based consensus protocols should provide security, consistency, reliability, and immutability of the maintained transaction ledger.…”