Research Unleashed
Introducing Reputation to Blockchain Systems By the end of the day on 22 May 2018, an unidentified hacker had made off with $18 Million in Bitcoin Gold. Over the long weekend leading up to that Tuesday, they had rented enough computing power to become the single most powerful member of the Bitcoin mining network. They used their newly bought power to commit fraud, making off with millions. The hacker was never caught, and today almost all blockchains remain vulnerable to the same type of attack. “The initial problem with blockchains,” Prof Paulo Esteves-Veríssimo explained, “is that they tried to solve a distributed systems problem relying only on cryptographic methods. I thought that if I could get a cryptographer to work with me on re-approaching the challenge, we could significantly improve the technology.” That’s how security expert Dr Jiangshan Yu joined Esteves-Veríssimo’s research group as a postdoctoral researcher at SnT in 2016. Together, they have developed a brand-new blockchain technology – and made blockchain’s
Jiangshan Yu joined SnT in 2016 to work on blockchain security. Today he is Associate Director of Research at the Monash Blockchain Technology Centre (Australia).
28
vulnerability to the type of attack that happened in 2018, referred to as a 51% attack, a thing of the past. They call their technology “Repucoin”. Unlike traditional blockchains (such as Bitcoin and Ethereum), Repucoin distributes power based on a user’s demonstrated reliability, which they call their “reputation”. “On a traditional blockchain,” Yu explained, “you need to trust the simple majority [as measured in terms of computing power]. We are saying, rather than trusting based on computing power alone, we should trust who has contributed the most often and most reliably”. Esteves-Veríssimo added “what we are creating here is a system built on trustworthiness. It is as concrete and dependable as physics: power equals work over time. That’s the equation.” Yu and Esteves-Veríssimo call this “integrated power”, as opposed to the “instantaneous” power relied on by traditional blockchains. With Repucoin, network participants slowly build their personal reputation scores over time. Then it uses these reputation scores to power its consensus finding. In order for an action to be agreed to on the network, it must have the support of participants whose collective reputation scores account for at least two thirds of the sum of all reputation points. Participants’ whose activity is found to be in bad faith take a hit to their reputation score, lowering their relative power on the network. “In a world that is too fast, we’ve reintroduced the value of slowly built trust,” said Esteves-Veríssimo. It is the first instance in which an articulation of trustworthiness has been built into a proof-of-work network (Bitcoin is also a proof-of-work network).
“Repucoin not only resists a 51% attack – it is robust against an 85% or even a 99% attack,” continued Esteves-Veríssimo. Given the effort required to build reputation on the system, any such attack becomes exorbitantly expensive. In fact, it would be over five-thousand times more expensive to attack Repucoin than Bitcoin, and as the network ages, Repucoin’s resilience will only improve. “We want Repucoin to be more than just another blockchain. It is a system upgrade to any existing blockchain,” Yu explained over Skype from his office in Australia, where he is Associate Director of Research of a new interdisciplinary centre working to develop the blockchain ecosystem. The centre, called the Monash Blockchain Technology Centre (MBTC), is helping to introduce blockchain into other disciplines and industries who can benefit from the technology, as well as working to continue improving blockchain’s suitability for real-world applications. The resilience that Repucoin brings to blockchain significantly increases its viability for many real-world applications, such as fintech, energy, food supply chains, health care, and smart cities. Moreover, insights gained through Yu and Esteves-Veríssimo’s work on Repucoin have been included in a survey of blockchain technology, which is now used as a teaching material by several universities. And that’s sure to be just the beginning. Thanks to support of an FNR PEARL Grant, and the ongoing collaboration with Yu’s Monash University team, we can be certain to hear a lot more about Repucoin’s impact on the blockchain revolution in the future •
