We present ConChord, a large-scale certificate distribution system built on a peer-to-peer distributed hash table. ConChord provides load-balanced storage while eliminating many of the administrative difficulties of traditional, hierarchical server architectures. ConChord is specifically designed to support SDSI, a fully-decentralized public key infrastructure that allows principals to define local names and link their namespaces to delegate trust. We discuss the particular challenges ConChord must address to support SDSI efficiently, and we present novel algorithms and distributed data structures to address them. Experiments show that our techniques are effiective and practical for large SDSI name hierarchies.