Digital archives protect important data collections from failures by making multiple copies at other archives, so that there are always several good copies of a collection. In a cooperative replication network, sites "trade" space, so that each site contributes storage resources to the system and uses storage resources at other sites. Here, we examine bid trading: a mechanism where sites conduct auctions to determine who to trade with. A local site wishing to make a copy of a collection announces how much remote space is needed, and accepts bids for how much of its own space the local site must "pay" to acquire that remote space. We examine the best policies for determining when to call auctions and how much to bid, as well as the effects of "maverick" sites that attempt to subvert the bidding system. Simulations of auction and trading sessions indicate that bid trading can allow sites to achieve higher reliability than the alternative: a system where sites trade equal amounts of space without bidding.

Storage outsourcing is a rising trend which prompts a number of interesting security issues, many of which have been extensively investigated in the past. However, Provable Data Possession (PDP) is a topic that has only recently appeared in the research literature. The main issue is how to frequently, efficiently and securely verify that a storage server is faithfully storing its client’s (potentially very large) outsourced data. The storage server is assumed to be untrusted in terms of both security and reliability. (In other words, it might maliciously or accidentally erase hosted data; it might also relegate it to slow or off-line storage.) The problem is exacerbated by the client being a small computing device with limited resources. Prior work has addressed this problem using either public key cryptography or requiring the client to outsource its data in encrypted form. In this paper, we construct a highly efficient and provably secure PDP technique based entirely on symmetric key cryptography, while not requiring any bulk encryption. Also, in contrast with its predecessors, our PDP technique allows outsourcing of dynamic data, i.e, it efficiently supports operations, such as block modification, deletion and append. 1.

1 Introduction Peer-to-peer systems form a useful architecture for awide range of important applications. Although the term "peer-to-peer " is often associated in the pub-lic imagination with Napster and related file-sharing systems, other important services that can be builton a peer-to-peer framework. For example, a group of digital libraries may cooperate with each other toprovide preservation by storing copies of each other's digital materials. In this system, each library acts asan autonomous peer in a distributed, heterogeneous collection replication mechanism. Such a commu-nity does not require a central controller to manage the replication of data; instead, each peer can com-municate with other peers to replicate its own collections. The result of individual libraries seekinglocally to preserve their own information by working with other peers is a global community in whichevery library's collections are protected.

Data compression algorithms change frequently, and obsolete decoders do not always run on new hardware and operating systems, threatening the long-term usability of content archived using those algorithms. Re-encoding content into new formats is cumbersome, and highly undesirable when lossy compression is involved. Processor architectures, in contrast, have remained comparatively stable over recent decades. VXA, an archival storage system designed around this observation, archives executable decoders along with the encoded content it stores. VXA decoders run in a specialized virtual machine that implements an OS-independent execution environment based on the standard x86 architecture. The VXA virtual machine strictly limits access to host system services, making decoders safe to run even if an archive contains malicious code. VXA’s adoption of a “native ” processor architecture instead of type-safe language technology allows reuse of existing “hand-optimized ” decoders in C and assembly language, and permits decoders access to performance-enhancing architecture features such as vector processing instructions. The performance cost of VXA’s virtualization is typically less than 15 % compared with the same decoders running natively. The storage cost of archived decoders, typically 30–130KB each, can be amortized across many archived files sharing the same compression method. 1

this paper we present recent and ongoing research projects of the Peers research group at Stanford University. Section 2 studies the problems relating to locating resources in P2P systems. Section 3 discusses work on resource allocation and aggregation. Section 4 focuses on issues of resource availability and authenticity. Note, this paper should not be construed as an overview of all research problems pertaining to peer-to-peer networks. Only projects connected to our Peers group are described. Additional citations can be found in the papers referenced below

Abstract. The Storage Exchange (SX) is a new platform allowing storage to be treated as a tradeable resource. Organisations with varying storage requirements can use the SX platform to trade and exchange storage services. Organisations have the ability to federate their storage, be-it dedicated or scavenged and advertise it to a global storage market. In this paper we discuss the high level architecture employed by our platform and investigate a sealed Double Auction market model. We implement and experiment the following clearing algorithms: maximise surplus, optimise utilisation and an efficient combination of both. 1

Digital archives protect important data collections from failures by making multiple copies at other archives, so that there are always several good copies of a collection. In a cooperative replication network, sites “trade ” space, so that each site contributes storage resources to the system and uses storage resources at other sites. Here, we examine bid trading: a mechanism where sites conduct auctions to determine who to trade with. A local site wishing to make a copy of a collection announces how much remote space is needed, and accepts bids for how much of its own space the local site must “pay ” to acquire that remote space. We examine the best policies for determining when to call auctions and how much to bid, as well as the effects of “maverick ” sites that attempt to subvert the bidding system. Simulations of auction and trading sessions indicate that bid trading can allow sites to achieve higher reliability than the alternative: a system where sites trade equal amounts of space without bidding.

Abstract. Peer-to-peer (P2P) networks are distributed data sharing systems with no dedicated and centralized infrastructure. These systems are attractive because they deliver on the Internet’s promise of true decentralization, offering scalability, availability, fault tolerance, robustness, and low barriers to entry. While P2P systems have been used so far mainly for file sharing, their true potential lies as a vast, loosely connected world wide infrastructure for sharing resources, data and information. However, many challenging research problems must be addressed and solved before this vision can materialize. This paper addresses a natural step in the evolution of P2P: going beyond simple file sharing based on exact-name based lookups to data and information sharing where data is accessed based on its attributes or properties. We have identified diverse applications such as network monitoring, astronomy data applications, event-notification systems, and Grid computing that can benefit directly from attribute-based access to distributed data over P2P systems. Based on the application requirements, we propose three new models for both data distribution and data accesses. For each of these models, we propose can and chord like structures for data storage and information retrieval. A novel aspect of our development is that one of the models identified is directly applicable for building contentbased publish/subscribe systems over P2P networks. 1

The preservation of literary hypertexts presents significant challenges if we are to ensure continued access to them as the underlying technology changes. Not only does such an effort involve standard digital preservation problems of representing and refreshing metadata, any constituent media types, and structure; hypertext preservation poses additional dimensions that arise from the work’s on-screen appearance, its interactive behavior, and the ways a reader’s interaction with the work is recorded. In this paper, we describe aspects of preservation introduced by literary hypertexts such as the need to reproduce their modes of interactivity and their means of capturing and using records of reading. We then suggest strategies for addressing the pragmatic dimensions of hypertext preservation and discuss their status within existing digital preservation schemes. Finally, we examine the possible roles various stakeholders within and outside of the hypertext community might assume, including several social and legal issues that stem from preservation.

The prevailing model for digital preservation is that archives should be similar to a “fortress”: a large, protective infrastructure built to defend a relatively small collection of data from attack by external forces. Such projects are a luxury, suitable only for limited collections of known importance and requiring significant institutional commitment for sustainability. In previous research, we have shown the web infrastructure (i.e., search engine caches, web archives) refreshes and migrates web content in bulk as side-effects of their user-services, and these results can be mined as a useful, but passive preservation service. Our current research involves a number of questions resulting from removing the implicit assumption that web-based data objects must passively await curatorial services: What if data objects were not tethered to repositories? What are the implications if the content were actively seeking out and injecting itself into the web infrastructure (i.e., search engine caches, web archives)? All of this leads to our primary research question: Can we create objects that preserve themselves more effectively than repositories or web infrastructure can?