ClaimChain is a Public Key Infrastructure unique in that it can operate in fully decentralized settings with no trusted parties. A vouching mechanism among users, similar to the Web of Trust, assists with social authentication but without revealing the users' social graph. High-integrity data structures prevent equivocation and help detect compromises; the protocol can support generic claims (conventional PGP, modern OTR/Signal etc.); and a prototype evaluation indicates that ClaimChain can scale.