Online content distribution has increasingly gained popularity among the entertainment industry and the consumers alike. A key challenge in online content distribution is a cost-efficient solution to handle demand peaks. To address this challenge, we propose Dandelion, a system for robust cooperative (peer-to-peer) content distribution. Dandelion explicitly addresses two crucial issues in cooperative content distribution. First, it provides robust incentives for clients who possess content to serve others. A client that honestly serves other clients is rewarded with credit that can be redeemed for future downloads at the content server. Second, Dandelion discourages unauthorized content distribution. A client that uploads to another client is rewarded for its service only after the server has verified the other client’s legitimacy. Our preliminary evaluation of a prototype system running on commodity hardware with 1 Mbps uplink and 1 Mbps downlink indicates that Dandelion can achieve aggregate client download throughput three orders of magnitude higher than the one achieved by an HTTP/FTP-like server. 1

An electronic cash system allows users to withdraw coins, represented as bit strings, from a bank or broker, and spend those coins anonymously at participating merchants, so that the broker cannot link spent coins to the user who withdraws them. A variety of schemes with various security properties have been proposed for this purpose, but because strings of bits are inherently copyable, they must all deal with the problem of double-spending. In this paper, we present an electronic cash scheme that introduces a new peer-to-peer system architecture to prevent double-spending without requiring an on-line trusted party or tamper-resistant software or hardware. The scheme is easy to implement, computationally efficient, and provably secure. To demonstrate this, we report on a proof-ofconcept implementation for Internet vendors along with a detailed complexity analysis and selected security proofs. 1.

Abstract—Content distribution via the Internet is becoming increasingly popular. To be cost-effective, commercial content providers are now using peer-to-peer (P2P) protocols such as BitTorrent to save bandwidth costs and to handle peak demands. When an online content provider uses a P2P protocol, it faces an incentive issue: how to motivate its clients to upload to their peers. This paper presents Dandelion, a system designed to address this issue. Unlike previous incentive-compatible systems, such as BitTorrent, our system provides non-manipulable incentives for clients to upload to their peers. A client that honestly uploads to its peers is rewarded in the following two ways. First, if its peers are unable to reciprocate its uploads, the content provider rewards the client’s service with credit. This credit can be redeemed for discounts on paid content or other monetary rewards. Second, if the client’s peers possess content of interest and have appropriate uplink capacity, the client is rewarded with reciprocal uploads from its peers. In designing Dandelion, we trade scalability for the ability to provide robust incentives for cooperation. The evaluation of our prototype system on PlanetLab demonstrates the viability of our approach. A Dandelion server that runs on commodity hardware with a moderate access link is capable of supporting up to a few thousand clients. These clients are able to download content at rates comparable to those of BitTorrent clients. Index Terms—Peer-to-peer, content distribution, incentives, fair-exchange, symmetric cryptography. I.

Abstract—As the sale of digital content is moving more and more online, the content providers are beginning to realize that bandwidth infrastructures are not easily scalable. The emergence of peer-to-peer content delivery networks present these providers with a way to overcome this limitation. However, such networks have so far been ad-hoc in nature. One of the main reason for this has been the lack of incentives for end users to contribute their bandwidth to the network. In this paper we present the design and implementation of a peer-to-peer protocol named Floodgate that provides a micropayment based incentive for peers to contribute their bandwidth. Floodgate implements an optimistic fair exchange protocol and is designed to be resilient against targeted attacks. Performance measurements, including those conducted over the PlanetLab infrastructure, show that Floodgate’s security and cryptographic overheads are low when compared against the standard BitTorrent implementation. I.

Abstract- Anonymity has received increasing attention in the literature due to the users ’ awareness of their privacy nowadays. Anonymity provides protection for users to enjoy network services without being traced. While anonymityrelated issues have been extensively studied in paymentbased systems such as e-cash and peer-to-peer (P2P) systems, little effort has been devoted to wireless mesh networks (WMNs). On the other hand, the network authority requires conditional anonymity such that misbehaving entities in the network remain traceable. Here, we propose security architecture to ensure unconditional anonymity for honest users and traceability of misbehaving users for network authorities in WMNs. The proposed architecture strives to resolve the conflicts between the anonymity and traceability objectives, in addition to guaranteeing fundamental security requirements including authentication, confidentiality, data integrity, and non repudiation.

Abstract: P2P networks suffer from the free-riding problem, wherein users connect to the network only to use the resources, but do not donate any resources themselves. A popular approach to overcome this problem is to reward peers who share their resources, through payments. This has given a fresh lease of life to micropayments schemes, which are now being used in such networks. P2P Micropayment schemes need to address several requirements like transferability, anonymity, etc. that are not met by many traditional micropayment schemes. They must utilize the distinctive features of a P2P network to maintain high efficiency, while providing optimum security. In this paper we list out the requirements that need to be kept in mind while designing such schemes, present a survey of existing schemes, and analyze them critically. We also give a comparison of the schemes with respect to security and performance.

Abstract — Often students have difficulties mastering cryptographic algorithms. For some time we have been developing with methods for introducing important security concepts for both undergraduate and graduate students in Information Systems, Computer Science and Engineering students. To achieve this goal, Sequence diagrams and spatial circuit derivation from equations are introduced to students. Sequence diagrams represent progression of events with time. They learn system security concepts more effectively if they know how to transform equations and high level programming language constructs into spatial circuits or special purpose hardware. This paper describes an active learning module developed to help students understand secure protocols, algorithms and modeling web applications to prevent attacks and both software and hardware implementations related to encryption. These course materials can also be used in computer organization and architecture classes to help students understand and develop special purpose circuitry for cryptographic algorithms. Keywords-e-cashless; transactions; cryptographic; algorithms; Sequence diagrams, Spatial circuits.