Paper 2021/818

CTng: Secure Certificate and Revocation Transparency

Hemi Leibowitz, Haitham Ghalwash, Ewa Syta, and Amir Herzberg

Abstract

In this work, we study Certificate Transparency (CT), an important standardized extension of classical Web-PKI, deployed and integrated into major browsers. We evaluate the properties of the published design of CT-v1 (RFC 6962), and identify five major concerns, which persist in drafts for CT-v2. Most significantly, CT-v1 fails to achieve the main goal of the original CT publications, namely security with No Trusted Third Party (NTTP) and it does not ensure transparency for revocation status. Several recent works address some of these issues but at the cost of significant, non-evolutionary deviation from the existing standards and ecosystem. In response, we present CTng, a redesign of CT. CTng achieves security, including transparency of certificate and of revocation status, with No Trusted Third Party, while preserving client’s privacy, allowing offline client validation of certificates, and facilitating resiliency to DoS. CTng is efficient and practical, and provides a possible next step in the evolution of PKI standards. We present a security analysis and an evaluation of our experimental open source prototype shows that CTng imposes acceptable communication and storage overhead.