Abstract. In this paper we investigate the notion of space efficient public-key infrastructure (PKI) directories. The area of PKI is relatively young and we do not know yet the long term implications of design decisions regarding PKI and its interface with applications. Our goal is to study mechanisms for networks and systems settings where the size of directories is a significant resource (due to space restrictions).
Naturally, the tools we employ are cryptographic hashing techniques combined with the tradeoffs of public storage and computation. Our mechanisms are quite simple, easy to implement and thus practical, yet they are quite powerful in making the operation substantially less costly (mainly) storage-wise and in trading storage for computation. In the past, tree based mechanisms were considered extensively to improve the complexity of PKI directories. We show that hashing techniques provide various advantages as well.