Cryptographic Proofs of Knowledge and Their Usage in Systems Protecting Digital Identity

habilitation thesis

English

This thesis deals with the fundamental building blocks of cryptographic systems for the protection of digital identity, especially with the cryptographic proofs of knowledge. The first part of the text contains the description and analysis of primitives used during the construction of modern protocols, in particular the cryptographic commitment schemes, interactive proof systems, $\Sigma$-protocols and proofs of knowledge. The analysis of primitives allows readers to understand current proposals of protocols and schemes for the digital identity protection, such as authentication, identification, access control systems, and systems with enhanced privacy protection, such as attribute-based authentication systems or anonymous credentials. The first part of the text, which is written as a complex introduction to the area of cryptographic protection of digital identity, contains also the current state analysis. In the next chapters, own cryptographic schemes based on aforementioned primitives are proposed. The schemes for physical access control, attribute-based authentication and secure data collection are specified. Using the proposals, the modularity and versatility of the primitives are demonstrated in various applications. The main contributions of the schemes are novel privacy-enhancing features and features for the identification of malicious users using revocation and de-anonymization methods. The existing systems either lack these features completely or provide only inefficient solutions that cannot be implemented on real devices. The efficiency of our methods is proven in the final chapter devoted to implementation aspects.

Cryptography, proofs of knowledge, digital identity, privacy, anonymity, attribute-based authentication, anonymous credentials.

HAJNÝ, J.

6. 4. 2016

VUTIUM

Brno

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