Certification with multiple signatures

Certificate Authority (CA) is a single point of failure in the design of Public Key Infrastructure (PKI). A single compromised CA breaks the entire infrastructure. The disclosed CA key can be used by adversaries to issue rogue certifi- cates for any domains without the consent of the domain owners. These rogue certificates have been used in Man-inthe- Middle (MitM) attacks. Studies have been conducted to prevent and reduce the damages of breached CAs and rogue certificates in diferent ways. However, few have a mechanism to fully and eficiently verify whether a CA or a certificate can be trusted or not. There is a need to develop new methods to ensure certificates with a high level of trustworthy in order for the PKI to be more resistant to compromised CAs and rogue certificates. We propose an alternative approach to mitigate the issue of CA breaches by imposing multiple signatures on a server certificate. This is analogous with the redundancy approach that is commonly adopted in the practice of IT management. Since CAs are run and managed by independent organizations, the probability of breaking multiple CAs in a short period of time is reduced significantly. If S signatures are imposed on a certificate, the compromise of S - 1 CAs will not break the PKI system. In this paper, we describe a framework of our approach and analyze its security. We also provide a brief overview of the most relevant counter measures against CA breaches and rogue certificates.