Trust Mends Blockchains: Living up to Expectations

Abstract

At the heart of Blockchains is the trustless leader election mechanism for achieving consensus among pseudoanonymous peers, without the need of oversight from any third party or authority whatsoever. So far, two main mechanisms are being discussed: proof-of-work (PoW) and proof-of-stake (PoS). PoW relies on demonstration of computational power, and comes with the markup of huge energy wastage in return of the stake in cyrpto-currency. PoS tries to address this by relying on owned stake (i.e., amount of crypto-currency) in the system. In both cases, Blockchains are limited to systems with financial basis. This forces non-crypto-currency Blockchain applications to resort to "permissioned" setting only, effectively centralizing the system. However, non-crypto-currency permisionless blockhains could enable secure and self-governed peer-to-peer structures for numerous emerging application domains, such as education and health, where some trust exists among peers. This creates a new possibility for valuing trust among peers and capitalizing it as the basis (stake) for reaching consensus. In this paper we show that there is a viable way for permisionless non-financial Blockhains to operate in completely decentralized environments and achieve leader election through proof-of-trust (PoT). In our PoT construction, peer trust is extracted from a trust network that emerges in a decentralized manner and is used as a waiver for the effort to be spent for PoW, thus dramatically reducing total energy expenditure of the system. Furthermore, our PoT construction is resilient to the risk of small cartels monopolizing the network (as it happens with the mining-pool phenomena in PoW) and is not vulnerable to sybils. We evluate security guarantees, and perform experimental evaluation of our construction, demonstrating up to 10-fold energy savings compared to PoW without trading off any of the decentralization characteristics, with further guarantees against risks of monopolization. Index Terms-Blockchain, Proof of Work, Bitcoin, Distributed Ledger, PoW is expensive, Proof of Trust, PoW alternative 1 We refer here to public Blockchains where identities are not managed. Although such systems are technically anonymous, they practically can only guarantee pseudo-anonymity depending on usage patterns and peers practices. 2 We differentiate between Blockchain, with big B, as the technology that comprises all the components of the system in terms of rules, mechanisms, protocols, etc., and between blockchain which refers to the ledger of chained blocks of transactions. 3 e.g., Ethereum Blockchain

ZkRep: A Privacy-Preserving Scheme for Reputation-Based Blockchain System

“…Thus, the reputation/trust concept has attracted considerable interest in the combination of blockchain and IoT research community [3], [4]. The core idea of reputation is to fully consider the heterogeneity property of the IoT devices, i.e., to quantify each validators' behavior/contribution so as to provide a basis for system improvement [3]- [6]. Such behavior could be the validator's contribution of block generation [3], [5]; or the participation in the BFT voting procedure [4]; or the trust link between each other [6].…”

“…The core idea of reputation is to fully consider the heterogeneity property of the IoT devices, i.e., to quantify each validators' behavior/contribution so as to provide a basis for system improvement [3]- [6]. Such behavior could be the validator's contribution of block generation [3], [5]; or the participation in the BFT voting procedure [4]; or the trust link between each other [6]. Recent works have successfully leveraged reputation to enhance the throughput and scalability of Byzantine Fault Tolerance (BFT)-based blockchains [4], [5] and reduce the energy costs of Proof-of-Work (PoW) systems [3], [6].…”

“…Such behavior could be the validator's contribution of block generation [3], [5]; or the participation in the BFT voting procedure [4]; or the trust link between each other [6]. Recent works have successfully leveraged reputation to enhance the throughput and scalability of Byzantine Fault Tolerance (BFT)-based blockchains [4], [5] and reduce the energy costs of Proof-of-Work (PoW) systems [3], [6]. Moreover, introducing reputation makes it smoother to integrate with incentive schemes [4], [6].…”

“…Recent works have successfully leveraged reputation to enhance the throughput and scalability of Byzantine Fault Tolerance (BFT)-based blockchains [4], [5] and reduce the energy costs of Proof-of-Work (PoW) systems [3], [6]. Moreover, introducing reputation makes it smoother to integrate with incentive schemes [4], [6].…”

“…However, existing reputation-enhanced blockchains [3]- [6] only consider the static adversary. Thus, they are particularly vulnerable to slowly adaptive attackers, who can first observe the system, and then choose a validator with a high reputation as the victim.…”