Afia, Ismail Sami Abdelaziz2025-05-012025-05-012025https://hdl.handle.net/1828/22092This dissertation presents advancements in privacy-preserving protocols, focusing on two research areas: policy-based sanitizable signature schemes and fair exchange mechanisms. Sanitizable signature schemes allow designated parties to modify or sanitize signed messages while preserving the message’s authenticity. We present the Unlinkable Policy-Based Sanitizable Signature (UP3S) scheme, which addresses a significant deficiency in existing policy-based sanitizable signature schemes, the lack of unlinkability. A crucial security property, particularly in privacy-sensitive applications, unlinkability guarantees that distinct sanitized versions of a given message cannot be linked to the original message or to each other, even across multiple sanitization operations. Building upon UP3S, we investigate extending its capabilities to support fine-grained control over message modifications. This involves enabling multiple modification policies for a single message and facilitating the delegation of sanitization rights. To this end, we propose the Traceable Policy-Based Signature (TPBS) scheme, which forms the basis for the Extended Policy-Based Sanitizable Signature (EP3S). EP3S offers a flexible and secure framework for policy-based sanitizable signatures, incorporating enhanced control over message modifications and sanitization-rights delegation. In the area of fair exchange mechanisms, our contributions focus on privacy-preserving exchanges of both digital and physical assets. We introduce V2VFx, a privacy-preserving framework for the fair exchange of physical assets, specifically in vehicle-to-vehicle energy trading. Together, these contributions advance the state of privacy-preserving protocols by addressing key limitations in existing schemes and extending their applicability.enAvailable to the World Wide Webdigital signaturessanitizable signaturespolicy-based sanitizable signaturesattribute-based signaturesattribute-based encryptionextended sanitizable signaturesThesisAfia, I., AlTawy, R.: Unlinkable policy-based sanitizable signatures. In: Cryptographers’ Track at the RSA Conference. pp. 191–221. Springer (2023)Afia, I., AlTawy, R.: Traceable policy-based signatures with delegation. In: International Conference on Cryptology and Network Security. pp. 51–72. Springer (2023)Afia, I., AlTawy, R.: Extended policy-based sanitizable signatures. In: Information Security and Cryptology, INSCRYPT. vol. 15544. Springer (2024)