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|Title||Increasing Privacy in Smart Contracts: Exploring Encryption Mechanisms|
|Institution||University of Zurich|
|Faculty||Faculty of Business, Economics and Informatics|
|Abstract Text||After the introduction of the concept of Smart Contracts (SC) in 1994, it took another decade until a use case was found. The blockchain's focus on transactions appeared to be a perfect ground to implement the concept of automated, self-executing contracts. Popular blockchains such as Ethereum tied the integration of SC closely to their core functionalities, using the programming language Solidity specifically introduced for this purpose. Since physical contracts know distinct security properties due to privacy requirements, the digital equivalents are expected to fulfill the same. However, the transfer of such properties are challenging as some blockchains are trustless systems and therefore no channel of communication between the two contracting parties is expected. In order to resolve this challenge, cryptographic mechanisms were introduced to ensure privacy by either encrypting the values on-chain and allow them to be read and manipulated by authorized contracting parties or using an o-chain approach, which outsources the storage and manipulation of sensitive data to a Trusted Third Party. Different encryption approaches were explored by implementing a simple transaction scenario using a SC with different types of data, showing limitations of each approach when using a on- or o-chain solution. Furthermore, performance of the encryption approaches were investigated in order to determine aspects, such as the contract size, the Gas used during the process and runtime. Finally, a comparison of all approaches was done, showing the difficulties of on-chain approaches for the chosen scenario and proposing some adjustments for further research to simplify the implementation. The evaluation showed a positive correlation between the complexity of the encryption mechanism and the three parameters mentioned, since the unencrypted approach used the least amount of memory or Gas and was the fastest, while the homomorphic approach was located at the other end of the scale.|