| Summary: | In recent years, blockchains have grown in popularity and the main reason for this growth is the set of properties that they provide, such as user privacy and a public record of transactions. This popularity is verifiable by the number of cryptocurrencies currently available and by the current market value of Bitcoin currency. Since its introduction, blockchain has evolved and another concept closely linked with it is smart-contract, which allows for more complex operations over the blockchain than simple transactions. Nevertheless, blockchain technologies have significant problems that prevent it to be adopted as a mainstream solution, or at least as an alternative to centralized solutions such as banking systems. The main one is its inefficiency, which is due to the need of a consensus algorithm that provides total order of transactions. Traditional systems easily solve this by having a single central entity that orders transactions, which can’t be done in decentralized systems. Thus, blockchain’s efficiency and scalability suffer from the need of time-costly consensus algorithms, which means that they can’t currently compete with centralized systems that provide a much greater amount of transactional processing power. However, with the emergence of novel processor architectures, secure hardware and trusted computing technologies (e.g. Intel SGX and ARM TrustZone), it became possible to investigate new ways of improving the inefficiency issues of blockchain systems, by designing better and improved blockchains. With all this in mind, this dissertation aims to build an efficient blockchain system that leverages trusted technologies, namely the Intel SGX. Also, a previous thesis will serve as a starting point, since it already implements a secure wallet system, that allows authenticated transactions between users, through the Intel SGX. As such, this wallet system will be extended to provide traceability of its transactions through a blockchain. This blockchain will use Intel SGX to provide an efficient causal consistency mechanism for ordering transactions. After this, the following step will be to support the execution of smart-contracts, besides regular transactions.
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