Secure and Privacy-preserving Decentralized Identities

This dissertation introduces a novel approach for decentralized, self-sovereign identities. With existing centralized identity providers, users have to trust their identity provider to not abuse the stored user data. The presented approach replaces the required trust into a single entity with verifiable trust into the correct functioning of the system. This is achieved based on smart contracts on the blockchain Ethereum, which represent the identities of the users. The privacy protection of the approach is evaluated and its functionality analyzed based on two use cases: the interaction with other smart contracts, and the use of voting for collaborative attribute assignments. To protect against malicious use of the pseudonymous identities, a Sybil defense approach is devised and integrated. Together, these approaches allow users to maintain self-sovereign identities, where the users remain in control over their own data.