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Vortrag der GI-Jahrestagung: Sicherheit in komplexen, vernetzten Umgebungen, Workshop im Rahmen der Jahrestagung 2005 der Gesellschaft für Informatik Informatik LIVE!, 19. - 22. September 2005 in Bonn, Deutschland
A fundamental problem that confronts peer-to-peer applications is the efficient location of the node that stores a desired data item. This paper presents Chord, a distributed lookup protocol that addresses this problem. Chord provides support for just one operation: given a key, it maps the key onto a node. Data location can be easily implemented on top of Chord by associating a key with each data item, and storing the key/data pair at the node to which the key maps. Chord adapts efficiently as nodes join and leave the system, and can answer queries even if the system is continuously changing. Results from theoretical analysis and simulations show that Chord is scalable: Communication cost and the state maintained by each node scale logarithmically with the number of Chord nodes.
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 higherlevel 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.
Peer-To-Peer systems are driving a major paradigm shift in the era of genuinely distributed computing. Gnutella is a good example of a Peer-To-Peer success story: a rather simple software enables Internet users to freely exchange files, such as MP3 music files. But it shows up also some of the limitations of current P2P information systems with respect to their ability to manage data eÆciently. In this paper we introduce P-Grid, a scalable access structure that is specifically designed for Peer-To-Peer information systems. P-Grids are constructed and maintained by using randomized algorithms strictly based on local interactions, provide reliable data access even with unreliable peers, and scale gracefully both in storage and communication cost.
The goal of a Public-Key-Infrastructure (PKI) is to prove whether a cryptographic public key is authentic for a certain user. This information is crucial for the reliability of asymmetric cryptographic methods. A widespread PKI has to handle an enormous number of queries for cryptographic certificates which attest the authenticity of public keys. For certain use cases a decentralized organization of the PKI is advantageously. Therefore the author developed a specialized Peer-to- Peer-PKI realizing efficient search and transfer of certificates and trust-recommendations. It is based on a combination of a logic calculus model for PKIs and a scalable Peer-to-Peer lookup protocol. This distributed approach offers advantages in comparison to hierarchical or centralized systems in terms of fault resistance, load distribution, self administration and independence of an operating organization.