On the 7th of July 2025 I finally finished my BSc-thesis and with this my bachelors degree. The thesis investigates if and how a certain kind of cryptographic signature scheme - the BBS signature scheme - can improve privacy in digital identity systems such as the Swiss E-ID. Here is the abstract:
Abstract
The digital transformation of identity systems holds the potential of making identification not only more convenient, but also more secure and privacy-respecting. However, the design of such systems must achieve a careful balance between security, usability, performance, interoperability, and the protection of user privacy. In Switzerland, the ongoing development of a state-issued electronic identity (E-ID) currently relies on the SD-JWT credential format with traditional ECDSA signatures. This architecture is functional and standards-compliant. However, it lacks the important privacy feature of unlinkability.
This thesis investigates the BBS (Boneh-Boyen-Shacham) signature scheme as a privacy-enhancing alternative. BBS natively allows holders to selectively disclose only the necessary parts of a credential and prevents different identifications from being linked over time and space. The thesis presents a theoretical analysis of BBS in the context of electronic identity systems and compares it to the existing SD-JWT/ECDSA setup.
To support this analysis, a practical implementation of BBS credential issuance and verification is developed and benchmarked. The results highlight the feasibility of integrating BBS in real-world identity systems and provide insights into its trade-offs in terms of performance and complexity. Ultimately, this work contributes to the broader discourse on privacy-preserving digital identity systems.
If you are interested in the full work, you can find the complete thesis here.