Peter Honeyman

Hide and seek: an introduction to steganography

Although people have hidden secrets in plain sight-now called steganography-throughout the ages, the recent growth in computational power and technology has propelled it to the forefront of todays security techniques. Essentially, the information-hiding process in a steganographic system starts by identifying a cover mediums redundant bits (those that can be modified without destroying that mediums integrity). The embedding process creates a stego medium by replacing these redundant bits with data from the hidden message. This article discusses existing steganographic systems and presents recent research in detecting them via statistical steganalysis. Here, we present recent research and discuss the practical application of detection algorithms and the mechanisms for getting around them.

WebCard: a java card web server

Webcard is a Java application that implements a TCP/IP stack and HTTP server and runs on a Schlumberger Cyberflex Access smartcard. In this report, we describe the architecture and implementation of Web-card and the constraints and assumptions that influenced its design. Complete sources for the application and its supporting environment are available.

Large files, small writes, and pNFS

Workload characterization studies highlight the prevalence of small and sequential data requests in scientific applications. Parallel file systems excel at large data transfers but sometimes at the expense of small I/O performance. pNFS is an NFSv4.1 high-performance enhancement that provides direct storage access to parallel file systems while preserving NFSv4 operating system and hardware platform independence. This paper demonstrates that distributed file systems can increase write throughput to parallel data stores---regardless of file size---by overcoming parallel file system inefficiencies. We also show how pNFS can improve the overall write performance of parallel file systems by using direct, parallel I/O for large write requests and a distributed file system for small write requests. We describe our pNFS prototype and present experiments demonstrating the performance improvements.

The LITTLE WORK project

Supporting software has not kept pace with the micro-miniaturization of microprocessor-based machines. The predominant operating system on such machines is MS-DOS, with no support for distributed computing. The goal of the LITTLE WORK project is to use off-the-shelf components to develop a mobile computing environment that is identical to that encountered in the office environment. Components identified as critical building blocks are the computer, the operating system, the file system, and communication. Each is examined. Development of a prototype machine is described.<<ETX>>

Nonmonotonic cryptographic protocols

The paper presents a new method for specifying and analyzing cryptographic protocols. The method offers several advantages over previous approaches. The technique is the first to allow reasoning about nonmonotonic protocols, which are needed for systems that rely on the deletion of information. There is no idealization of protocols; we specify at a level that is close to the actual implementation. We show how the method uncovers the known flaw in the Needham and Schroeder protocol (R.M. Needham and M.D. Schroeder, 1978). We then apply the method to the khat protocol (A.D. Rubin, P. Honeyman, 1993). The analysis reveals a serious, previously undiscovered flaw in the nonmonotonic protocol for long-running jobs.<<ETX>>

Communications and consistency in mobile file systems

To overcome the availability, latency, bandwidth, and cost barriers of mobile networks, mobile clients of distributed file systems switch between connected and disconnected modes of operation. Lying between these are modes of operation that refine the consistency semantics of cached files, allowing a mobile client to select a mode appropriate for the prevailing network conditions. Clients can take advantage of network opportunities unsuitable for connected operation, obtaining improved performance, more effective sharing, and more stringent consistency guarantees as a result. Todays mobile computing technology lets nomadic users operate computers large and small from their offices and homes and places in between. However, mobile users are often frustrated by the quality of distributed services available to them. In this article, we describe ways to extend the advantages of distributed file systems to users of mobile computers.

Evaluating delayed write in a multilevel caching file system

Delayed write in a multilevel file system cache hierarchy offers a way to improve performance in diverse client/server scenarios, such as integrating mass store into a distributed file system or providing distributed file system access over low-speed links. Using file system traces and cache simulations, we explore extensions and modifications to the traditional client-caching model employed in such file systems as AFS, Sprite, and DFS. High cache hit rates at an intermediate cache server-a machine logically interposed between clients and servers that provides cached file service to the clients-combined with high client cache hit rates lend practicality to an integrated mass storage file system. In such a system, magnetic tape or optical-based mass storage devices may be used as a first-class data repository, fronted by disk and RAM caches to offer acceptable access times to the large, but slow, mass storage system. Similarly, a high cache hit rate is necessary for users accessing file systems via low-speed links, where a delayed write intermediate caching server can mediate traffic to make better use of available bandwidth. In an example taken from mobile computing, an intermediate server might be used as a docking station at a users home. This arrangement would be convenient for users of mobile computers who upload large amounts of data generated while operating in disconnected mode. Simulations of delayed write caching strategies are applicable to both the mass storage and low-speed link scenarios.

GridNFS: global storage for global collaborations

uGridNFS combines the NFSv4 protocol and a collection of supporting middleware services configured to run in a Globus environment. GridNFS provides a file system name space that spans a virtual organization, security that meshes with Globus, fine-grained access control lists to support virtual organization groups and users, and secure file system access for jobs scheduled in an indeterminate future. By combining and integrating standard Internet protocols, GridNFS remains fully compatible with standards-compliant desktop and enterprise network services. Furthermore, GridNFS middleware enhances those environments with global naming and facile identity representation for agile access control across security domains.

Integrating mass storage and file systems

The authors describe current and anticipated work at the Center for Information Technology Integration at the University of Michigan in developing and integrating mass storage with distributed file systems, specifically with the Andrew File System (AFS). They present a specific approach to integrating AFS with mass storage: they consider the mass store itself to be the file system, not a bag on the side of a disk-based file system. Instead of developing a back-end server to manage the movement of data files between traditional disk-based storage systems (used, in the present case, by AFS) and magnetic-tape or optical-based mass storage systems (of which AFS has little or no knowledge), the authors envision the mass store as a first-class data repository. A traditional disk-based file system serves as a very large cache of the mass store system. On top of that is another, large, high-speed memory cache. All storage other than the mass store is used exclusively for caching. In this approach, cache management policies are of fundamental importance.<<ETX>>

Direct-pNFS: scalable, transparent, and versatile access to parallel file systems

Grid computations require global access to massive data stores. To meet this need, the GridNFS project aims to provide scalable, high-performance, transparent, and secure wide-area data management as well as a scalable and agile name space. While parallel file systems give high I/O throughput, they are highly specialized, have limited operating system and hardware platform support, and often lack strong security mechanisms. Remote data access tools such as NFS and GridFTP overcome some of these limitations, but fail to provide universal, transparent, and scalable remote data access. As part of GridNFS, this paper introduces Direct-pNFS, which builds on the NFSv4.1 protocol to meet a key challenge in accessing remote parallel file systems: high-performance and scalable data access without sacrificing transparency, security, orportability. Experiments with Direct-pNFS demonstrate I/O throughput that equals or out performs the exported parallel file system across a range of workloads.