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KORGAN: An Efficient PKI Architecture Based on Permissioned-Blockchain by Modifying PBFT Through Dynamic Threshold Signatures

During the last decade, several misbehaving Certificate Authorities (CA) have issued fraudulent TLS certificates allowing MITM kinds of attacks which result in serious security incidents. In order to avoid such incidents, Yakubov et al. recently proposed a new PKI architecture where CAs issue, revoke, and validate X.509 certificates on a public blockchain. In their proposal, each CA has a smart contract on the blockchain for publishing the hash values of its issued certificates and managing their revocation status. However, their proposal has several security and privacy issues. First, TLS clients can only validate certificates through either full nodes or web services, but cannot verify the correctness of the incoming responses. Second, certificate transparency is not fully provided because CAs do not store the certificates themselves but only their hash values in the blockchain which makes to detect fake ones impossible. In this paper, we eliminate the issues of the Yakubov et al.’s scheme and propose a new PKI architecture based on permissioned blockchain with a modified PBFT consensus mechanism. In our modified PBFT, the validators (i.e., the consensus nodes) utilize a dynamic threshold signature scheme to generate signed blocks. In this way, the trust to external entities can be completely eliminated during certificate validation. More concretely, TLS clients can easily verify the genuinity of the final state of the TLS certificates using signed block headers and the Merkle proofs. Also, the privacy of the TLS clients is fully preserved during validation process by avoiding additional communication with the external entities. Our scheme enjoys the dynamic property of the threshold signature because TLS clients do not have to change the verification key even if the validator set is dynamic. Furthermore, TLS clients are also not required to be a peer of the blockchain network and avoid communication overhead. We implement our proposal on private Ethereum network to demonstrate the experimental results. The results show that our proposal has negligible overhead during TLS handshake. The certificate validation duration is less than the duration in the conventional PKI and Yakubov et al.’s scheme.