Certificate Transparency Using Blockchain

The security of web communication via the SSL/TLS protocols relies on safe distributions of public keys associated with web domains in the form of X.509 certificates. Certificate authorities (CAs) are trusted third parties that issue these certificates. However, the CA ecosystem is fragile and prone to compromises. Starting with Google's Certificate Transparency project, a number of research works have recently looked at adding transparency for better CA accountability, effectively through public logs of all certificates issued by certification authorities, to augment the current X.509 certificate validation process into SSL/TLS. In this paper, leveraging recent progress in blockchain technology, we propose a novel system, called CTB, that makes it impossible for a CA to issue a certificate for a domain without obtaining consent from the domain owner. We further make progress to equip CTB with certificate revocation mechanism. We implement CTB using IBM's Hyperledger Fabric blockchain platform. CTB's smart contract, written in Go, is provided for complete reference.