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The huge success of eBay has proven the demand for customer-to-customer (C2C) electronic commerce. eBay is a centralized infrastructure with all its scalability problems (network bandwidth, server load, availability, etc.). In this paper we argue that C2C e-commerce is an application domain that maps naturally onto the emergent field of P2P systems simply by its underlying interaction model of customers, i.e., peers. This offers the opportunity to take P2P systems beyond mere file sharing systems into interesting new application domains. The long-term goal would be to design a fully functional decentralized system which resembles eBay without eBay's dedicated, centralized infrastructure. Since security (authenticity, non-repudiation, trust, etc.) is key to any e-commerce infrastructure, our envisioned P2P e-commerce platform has to address this adequately. As the first step in this direction we present an approach for a completely decentralized P2P public key infrastructure (PKI) which can serve as the basis for higher-level security service. In contrast to other systems in this area, such as PGP which uses a ``web of trust'' concept, we use a statistical approach which allows us to provide an analytical model with provable guarantees, and quantify the behavior and specific properties of the PKI. To justify our claims we provide a first-order analysis and discuss its resilience against various known threats and attack scenarios. In support of our belief that C2C E-commerce is one of the potential killer applications of the emerging structured P2P systems, we provide a layered model for P2P E-commerce, demonstrating the dependencies of various security related issues that can be built on top of a decentralized PKI.