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Research and Advances

Superimposing encrypted data

Much has been written about the necessity of processing data in the encrypted form. However, no satisfactory method of processing encrypted data has been published to date. Ahitub et al. [2] have analyzed the possibilities of using some special algorithms to add encrypted data. Rivest et al. [10] have suggested the use of an algorithm based on homomorphic functions for processing encrypted data. The main limitation of this algorithm is that such functions can be broken by solving a set of linear equations, as noted by [2]. The public-key crytosystem described in [11] can be used to multiply encrypted data but cannot be used to add encrypted data and is therefore not appropriate for some practical applications such as bank transactions. Abadi, Feigenbaum and Kilian [1] presented some general theorems concerning the problem of computing with encrypted data and formulated a framework to prove precise statements about what an encrypted instance hides and reveals; they also described encryption schemes for some well-known functions.
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Opinion

Technical correspondence

This note proposes an optimization to an algorithm published by T.E. Gerasch in his article “An Insertion Algorithm for a Minimal Internal Path Length Binary Search Tree” (Communications of the ACM, May 1988, pp. 579-585).
Research and Advances

The impact of information systems on organizations and markets

The adoption of information technology (IT) in organizations has been growing at a rapid pace. The use of the technology has evolved from the automation of structured processes to systems that are truly revolutionary in that they introduce change into fundamental business procedures. Indeed, it is believed that “More than being helped by computers, companies will live by them, shaping strategy and structure to fit new information technology [25].” While the importance of the relationship between information technology and organizational change is evidenced by the considerable literature on the subject,1 there is a lack of comprehensive analysis of these issues from the economic perspective. The aim of this article is to develop an economic understanding of how information systems affect some key measures of organization structure.
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Research and Advances

An empirical study of the reliability of UNIX utilities

The following section describes the tools we built to test the utilities. These tools include the fuzz (random character) generator, ptyjig (to test interactive utilities), and scripts to automate the testing process. Next, we will describe the tests we performed, giving the types of input we presented to the utilities. Results from the tests will follow along with an analysis of the results, including identification and classification of the program bugs that caused the crashes. The final section presents concluding remarks, including suggestions for avoiding the types of problems detected by our study and some commentary on the bugs we found. We include an Appendix with the user manual pages for fuzz and ptyjig.
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Research and Advances

Real-time data acquisition at mission control

Perhaps one of the most powerful symbols of the United States' technological prowess is the Mission Control Center (MCC) at the Lyndon B. Johnson Space Center in Houston. The rooms at Mission Control have been witness to major milestones in the history of American technology such as the first lunar landing, the rescue of Skylab, and the first launch of the Space Shuttle. When Mission Control was first activated in the early 1960s it was truly a technological marvel. This facility, however, has received only modest upgrades since the Apollo program. Until recently it maintained a mainframe-based architecture that displayed data and left the job of data analysis to flight controllers. The display technology utilized in this system was monochrome and primarily displayed text information with limited graphics (photo 1).An example display of 250 communication parameters is shown in Figure 1. The mainframe processed incoming data and displayed it to the flight controllers; however it performed few functions to convert raw data into information. The job of converting data into information upon which flight decisions could be made was performed by the flight controllers. In some cases, where additional computational support was required, small offline personal computers were added to the complex. Flight controllers visually copied data off the console display screens, and manually entered the data into the small personal computers where offline analysis could be performed.Although this system was technologically outdated, it contained years of customizing efforts and served NASA well through the early Space Shuttle program. Several factors are now driving NASA to change the architecture of Mission Control to accommodate advanced automation. First is the requirement to support an increased flight rate without major growth in the number of personnel assigned to flight control duties.A second major concern is loss of corporate knowledge due to the unique bimodal age distribution of NASA staff. Hiring freezes between the Apollo and Shuttle programs have resulted in NASA being composed of two primary groups. Approximately half of NASA consists of Apollo veterans within five years of retirement. The other half consists of personnel under the age of 35 with Shuttle-only experience. NASA considers it highly desirable to capture the corporate knowledge of the Apollo veterans in knowledge-based systems before they retire. Because the mainframe complex is primarily oriented to data display, it is a poor environment for capturing and utilizing knowledge.These factors have resulted in aggressive efforts by NASA's Mission Operations Directorate to utilize the following: a distributed system of Unix engineering-class workstations to run a mix of online real-time expert systems, and traditional automation to allow flight controllers to perform more tasks and to capture the corporate knowledge of senior personnel. Starting with the first flight of the Space Shuttle after the Challenger accident, the Real-Time Data System (RTDS) has played an increasingly significant role in the flight-critical decision-making process.
Research and Advances

Experiences with the Amoeba distributed operating system

The Amoeba project is a research effort aimed at understanding how to connect multiple computers in a seamless way [16, 17, 26, 27, 31]. The basic idea is to provide the users with the illusion of a single powerful timesharing system, when, in fact, the system is implemented on a collection of machines, potentially distributed among several countries. This research has led to the design and implementation of the Amoeba distributed operating system, which is being used as a prototype and vehicle for further research. In this article we will describe the current state of the system (Amoeba 4.0), and show some of the lessons we have learned designing and using it over the past eight years. We will also discuss how this experience has influenced our plans for the next version, Amoeba 5.0. Amoeba was originally designed and implemented at the Vrije Universiteit in Amsterdam, and is now being jointly developed there and at the Centrum voor Wiskunde en Informatica, also in Amsterdam. The chief goal of this work is to build a distributed system that is transparent to the users. This concept can best be illustrated by contrasting it with a network operating system, in which each machine retains its own identity. With a network operating system, each user logs into one specific machine—his home machine. When a program is started, it executes on the home machine, unless the user gives an explicit command to run it elsewhere. Similarly, files are local unless a remote file system is explicitly mounted or files are explicitly copied. In short, the user is clearly aware that multiple independent computers exist, and must deal with them explicitly. In contrast, users effectively log into a transparent distributed system as a whole, rather than to any specific machine. When a program is run, the system—not the user—decides upon the best place to run it. The user is not even aware of this choice. Finally, there is a single, system-wide file system. The files in a single directory may be located on different machines, possibly in different countries. There is no concept of file transfer, uploading or downloading from servers, or mounting remote file systems. A file's position in the directory hierarchy has no relation to its location. The remainder of this article will describe Amoeba and the lessons we have learned from building it. In the next section, we will give a technical overview of Amoeba as it currently stands. Since Amoeba uses the client-server model, we will then describe some of the more important servers that have been implemented so far. This is followed by a description of how wide-area networks are handled. Then we will discuss a number of applications that run on Amoeba. Measurements have shown Amoeba to be fast, so we will present some of our data. After that, we will discuss the successes and failures we have encountered, so that others may profit from those ideas that have worked out well and avoid those that have not. Finally we conclude with a very brief comparison between Amoeba and other systems. Before describing the software, however, it is worth saying something about the system architecture on which Amoeba runs.

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