• blockchain
• certification transparency
• decentralized identity
• ethereum
• public key infrastructure
• rogue certificates
• self-sovereign identity
• smart contract
• solidity

The Public-Key Infrastructure (PKI) relies on the trustworthiness of Certification Authorities (CAs), who are in charge to sign SSL/TLS certificates binding a public key with someone in the digital domain. CAs as trust anchors permit clients to be sure that who provides a SSL/TLS certificate is controlled by the CA and is a benevolent entity in the digital environment. However, attackers may force the CA to sign a fraudulent certificate, as reported from recent CA's incidents.
This research mitigates a potential exploit of the most critical vulnerability in the traditional PKI: a single compromised CA creates a breach in the security of digital communication (single point of failure). To solve this critical security issue, we defined a solution that exploits the Self-Sovereign Identity (SSI) paradigm and Distributed Ledger Technology (DLT) to allow users more control over their digital certificates and decentralized verification and managements of digital certificates, thus ensuring identity and trust without the need for centralized intermediaries.
For greater compatibility with the traditional scheme, our solution is based on a Decentralized Certificate Transparency (DCT) mechanism, which brings some benefits compared to traditional CT, highly centralized, while keeping the centrality of CAs unchanged. The proposed solution is compatible with X.509 PKI, giving more guarantees about certificate's trustworthy with a DCT designed on a SSI infrastructure. The DLT is used as a robust blockchain data registry for supporting the verification of both the user identity and the digital certificates. Decentralized IDentifiers (DIDs) are used to identify users and prove control over their web servers, giving the web server the capability to publish its SSL/TLS certificate's fingerprints as public logs for clients. Web servers have full control on the DCT without relying on CA's activity on those public logs. Client's browser must communicate with the blockchain data registry only to read information about certificates and to verify digital the reliability of the certificates. We collected real data about SSL/TLS certificates of several web service providers from different categories (including e-commerce platforms, educational institutions, government services, and healthcare) and implemented a prototype with a Solidity smart contract language and a JavaScript code to simulate both client and web server behavior during a TLS handshake. Performance evaluations show a reasonable overhead necessary to implement rogue certificate's detection despite a compromised CA.