Secure Distributed Systems Over Satoshi Blockchains

Abstract

Distributed Ledger Technologies (DLTs) have become an important driving force towards the creation of novel distributed applications aimed at solving problems that range from digital currency tools to self governing digital democracy systems. Our thesis is that Satoshi cryptocurrencies, i.e., Bitcoin and its variants, can be used to endow several popular distributed services with strong privacy, anonymity and censorship resistance properties that evade current solutions. To this end, we first study the design of Satoshi cryptocurrency mining protocols, and discover and document privacy and integrity vulnerabilities of Stratum, the de-facto pooled mining protocol. We have developed tools that exploit these vulnerabilities and have measured their impact and effectiveness under a rigorous academic context. Further, we have designed and implemented Bedrock, a solution that addresses these vulnerabilities. We have evaluated Bedrock in the live Bitcoin ecosystem and show that it achieved orders of magnitude better performance than traditional solutions like TLS and blanket encryption. We further introduce DLSS, a censorship-resistant, distributed ledger storage system that embeds client content into Satoshi transactions and organize it for fast search, recovery and reconstruction among hundreds of millions of financial transactions. DLSS distinguishes and exploits the singularities of different types of communications under censorship conditions. We design, implement and evaluate novel smart contracts tailored to the needs of censored users. For instance, we introduce difficult to censor and undetectable techniques to embed small quantities of data on Satoshi transactions, to be used for communications flowing out of the censored area that need to avoid detection by all-powerful censors. We also introduce techniques that prioritize cost optimization for storing large content flowing into the censored area, where uncensorability is the only priority. Further, we leverage our blockchain-writing constructs to introduce a novel perspective for traditionally hard problems of censorship resistance, private e-mail and secure port-knocking with surreptitious authentication and logging. We prove the security, privacy and anonymity of our smart contracts, and argue they impose unpalatable collateral damage to would-be censors. We build a monitoring and instrumentation framework for evaluating our constructs in the Litecoin cryptocurrency. We evaluate our blockchain-writing constructs by persisting hundreds of MBs of BBC news articles and censored software in the live Litecoin blockchain, where they are available to access for free anywhere in the world. We show that our solutions achieve storage throughput, blockchain utilization, and cost efficiency that improve by 2-4 orders of magnitude on state-of-the-art blockchain-writing solutions.