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Enhancing Privacy in a Blockchain-based Public Key Infrastructure

With the increasing need for, and the popularity of asymmetric cryptosystems, the need for a secure and efficient means of disseminating authentic public keys in a closed network is also on the increase[1]. Blockchain technology has been proposed as a solution to the security problems in the conventional models of a Public Key Infrastructure, as it offers transparency in the issuance of certificates and eliminates single points of failure. Blockchain excludes manipulation by making it computationally infeasible to edit a public key once it is published, thereby facilitating frequent key-updates. But this raises a concern about two issues - privacy and the proof of ownership, and ensuring one excludes the other. To reconcile these two seemingly irreconcilable problems, we propose a new key generation and update procedure, which will enable an identity to update its key with privacy and also to flawlessly prove the ownership of its past keys. Elliptic Curve Cryptographic methods are incorporated to make the cryptosystem secure. Further, the existence check of identities is optimised using multiple instances of bloom filter probabilistic data structures.