Elaphurus: Ensemble Defense Against Fraudulent Certificates in TLS

Recent security incidents indicate that certificate authorities (CAs) might be compromised to sign certificates with fraudulent information. The fraudulent certificates are exploited to launch successful TLS man-in-the-middle (MitM) attacks, even when TLS clients strictly verify the server certificates. Various security-enhanced certificate verification schemes have been proposed to defend against fraudulent certificates, such as Pinning, CAge, CT, DANE, and DoubleCheck. However, none of the above schemes perfectly solves the problem, which hinders them from being widely deployed. This paper analyzes these schemes in terms of security, usability and performance. Based on the analysis, we propose Elaphurus, an integrated security-enhanced certificate verification scheme on the TLS client side. Elaphurus is designed on top of Pinning, while integrating other schemes to eliminate their disadvantages and improving the overall security and usability. We implement the prototype system with OpenSSL. Experimental results show that it introduces a reasonable overhead, while effectively enhancing the security of certificate verification.