Privacy-preserving protocols: Advancing security and flexibility with policy-based sanitizable signatures and fair exchange mechanisms
Date
2025
Authors
Afia, Ismail Sami Abdelaziz
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Abstract
This 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.
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Keywords
digital signatures, sanitizable signatures, policy-based sanitizable signatures, attribute-based signatures, attribute-based encryption, extended sanitizable signatures