CertLedger: A New PKI Model with Certificate Transparency Based on Blockchain (1806.03914v2)

Abstract: In conventional PKI, CAs are assumed to be fully trusted. However, in practice, CAs' absolute responsibility for providing trustworthiness caused major security and privacy issues. To prevent such issues, Google introduced the concept of Certificate Transparency (CT) in 2013. Later, several new PKI models (e.g., AKI, ARPKI, and DTKI) are proposed to reduce the level of trust to the CAs. However, all of these proposals are still vulnerable to split-world attacks if the adversary is capable of showing different views of the log to the targeted victims. In this paper, we propose a new PKI architecture with certificate transparency based on blockchain, what we called CertLedger, to eliminate the split-world attacks and to provide an ideal certificate/revocation transparency. All TLS certificates, their revocation status, entire revocation process, and trusted CA management are conducted in the CertLedger. CertLedger provides a unique, efficient, and trustworthy certificate validation process eliminating the conventional inadequate and incompatible certificate validation processes implemented by different software vendors. TLS clients in the CertLedger also do not require to make certificate validation and store the trusted CA certificates anymore. We analyze the security and performance of the CertLedger and provide a comparison with the previous proposals.

• The paper introduces CertLedger, a blockchain model that prevents split-world attacks by decentralizing certificate transparency.
• It employs a transparent ledger for both certificate issuance and revocation, reducing reliance on vulnerable Certificate Authorities.
• The approach enhances privacy and scalability, offering robust security analysis and clear audit mechanisms for managing trusted CAs.

CertLedger: A Blockchain-Based PKI Model for Enhanced Certificate Transparency

The paper "CertLedger: A New PKI Model with Certificate Transparency Based on Blockchain" presents an innovative and technically rigorous approach to Public Key Infrastructure (PKI) and certificate transparency by leveraging blockchain technology. The authors, Murat Yasin Kubilay, Mehmet Sabır Kiraz, and Hacı Ali Mantar, aim to address long-standing vulnerabilities in traditional PKI systems, primarily focusing on split-world attacks and the weaknesses of Certificate Authorities (CAs).

Key Contributions and Methodology

The proposed model, CertLedger, introduces a decentralized approach to certificate and revocation transparency by utilizing blockchain's immutable and distributed ledger capabilities. This paradigm shift aims to eliminate the dependency on potentially malicious or compromised CAs, which have historically been single points of failure in PKI systems.

CertLedger's significant contributions can be summarized as follows:

1. Split-world Attack Prevention: By ensuring that all TLS certificates and their revocation statuses are stored on a blockchain, CertLedger mitigates the risk of split-world attacks, where inconsistent views of the log can be exploited by adversaries.
2. Decentralized Revocation Transparency: CertLedger enables both domain owners and CAs to initiate the revocation of certificates transparently, reducing reliance on CAs and mitigating issues arising from compromised certificate status verification mechanisms like CRLs and OCSPs.
3. Unified and Efficient Certificate Validation: The blockchain-based architecture inherently verifies certificate authenticity, eliminating the need for TLS clients to perform complex certificate validation processes and manage trusted CA certificates independently.
4. Privacy Preservation: With CertLedger, certificate validation does not require direct interaction with the certifying entities during the TLS handshake, thus preserving the privacy of client browsing histories compared to existing protocols like OCSP stapling.
5. Transparent CA Management: The proposal includes an audit mechanism by a CertLedger Board, ensuring only compliant CAs are trusted. It also incorporates fraud reporting and CA accountability, thus improving trust in CA operations.

Strong Numerical Results and Security Analysis

CertLedger is rigorously analyzed for its security properties, with a focus on its resilience against split-world attacks. The blockchain's consensus mechanism ensures a single, consistent view of all certificate states, thereby inherently providing robustness against many forms of PKI-oriented attacks. The researchers effectively demonstrate how CertLedger eliminates issues with current revocation mechanisms and reduces the need for trusted key management within TLS clients.

Moreover, CertLedger addresses scalability and performance concerns, highlighting storage and computational efficiencies. The architecture ensures that even resource-constrained clients can participate without substantial overhead, as they only need to maintain concise book-keeping through blockchain headers rather than entire ledgers.

Implications and Future Developments

The implications of CertLedger in the field of PKI are substantial. By decentralizing certificate and trust management, it redefines security guarantees that have been traditionally brittle due to CA-centric approaches. The model reduces complexity and the potential for human error in certificate validation processes.

As a forward-looking development, the paper suggests potential implementations within existing blockchain platforms like Ethereum, reinforcing the adaptability and practicality of the proposal. The authors also envision further enhancements in CA management automation, potentially leading to a fully autonomous and self-governing PKI ecosystem.

In conclusion, CertLedger represents a promising evolution in certificate transparency and management, offering improvements in security, efficiency, and privacy. Its adoption could reshape the trust infrastructure of the internet, mitigating long-standing risks associated with conventional PKI implementations. This technical proposal paves the way for future research and deployment scenarios where certificate management is decentralized and inherently reliable.