Authcoin is an alternative approach to the commonly used public key infrastructures such as central authorities and the PGP web of trust. It combines a challenge response-based validation and authentication process for domains, certificates, email accounts and public keys with the advantages of a block chain-based storage system. As a result, Authcoin does not suffer from the downsides of existing solutions and is much more resilient to sybil attacks.
Leiding, Benjamin; Cap, Clemens H.; Mundt, Thomas; and Rashidibajgan, Samaneh, "Authcoin: Validation and Authentication in Decentralized Networks" (2016). MCIS 2016 Proceedings. 5.