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Banking as an essential service can be hard to access in remote, rural regions where the network connectivity is intermittent. Although micro-banking has been made possible by SMS or USSD messages in some places, their security flaws and session-based nature prevent them from a wider adoption. Global level cryptocurrencies enable low-cost, secure and pervasive money transferring among distributed peers, but are still limited in their ability to reach more people in remote communities.We proposed to take advantage of the delay-tolerant nature of blockchains to deliver banking services to remote communities that only connect to the broader Internet intermittently. Using a base station that offers connectivity within the local area, regular transaction processing is solely handled by blockchain miners. The bank only joins to process currency exchange requests, reward miners and track user balances when the connection is available. By distributing the verification and storage tasks among peers, our system design saves on the overall deployment and operational costs without sacrificing the reliability and trustworthiness. Through theoretical and empirical analysis, we provided insights to system design, tested its robustness against network disturbances, and demonstrated the feasibility of implementation on off-the-shelf computers and mobile devices. 1

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The vulnerability of traditional blockchains have been demonstrated at multiple occasions. Various companies are now moving towards Proof-of-Authority (PoA) blockchains with more conventional Byzantine fault tolerance, where a known set of n permissioned sealers among which no more than t are Byzantine seal blocks that include user transactions. Despite their wide adoption, these protocols were not proved correct.In this paper, we present the Cloning Attack against the two mostly deployed PoA implementations of Ethereum, namely Aura and Clique. The Cloning Attack consists in one sealer cloning its key-value pair into two distinct Ethereum instances that communicate with distinct groups of sealers. To identify their vulnerabilities, we first specified the corresponding algorithms. We then infer the topology of the largest PoA network, POA Core, through active measurement. We deploy one testnet for each protocol and demonstrate the success of the attack with only one byzantine sealer. Finally, we propose counter-measures that prevent an adversary from double spending.

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