Peter Lutz

Relaxation methods for image reconstruction

The problem of recovering an image (a function of two variables) from experimentally available integrals of its grayness over thin strips is of great importance in a large number of scientific areas. An important version of the problem in medicine is that of obtaining the exact density distribution within the human body from X-ray projections. One approach that has been taken to solve this problem consists of translating the available information into a system of linear inequalities. The size and the sparsity of the resulting system (typically, 25,000 inequalities with fewer than 1 percent of the coefficients nonzero) makes methods using successive relaxations computationally attractive, as compared to other ways of solving systems of inequalities. In this paper, it is shown that, for a consistent system of linear inequalities, any sequence of relaxation parameters lying strictly between 0 and 2 generates a sequence of vectors which converges to a solution. Under the same assumptions, for a system of linear equations, the relaxation method converges to the minimum norm solution. Previously proposed techniques are shown to be special cases of our procedure with different choices of relaxation parameters. The practical consequences for image reconstruction of the choice of the relaxation parameters are discussed.

Behavior-Based covert channel in cyberspace

Many covert channels take advantages of weaknesses, flaws, or unused data fields in network protocols. In this paper, a behavior-based covert channel, that takes advantages of behavior of an application, is presented along with a formal definition in the framework of finite state machines. The behavior-based covert channel is application specific and lies at the application layer of the network OSI model, which makes the detection of this type of covert channel much more dicult. A detailed sample implementation demonstrates an example of this type of covert channel in the form of a simple online two-person game.The potential of this type of covert channel is also discussed.

Iterative relaxation methods for image reconstruction

The problem of recovering an image (a function of two variables) from experimentally available integrals of its grayness over thin strips is of great importance in a large number of scientific areas. An important version of the problem in medicine is that of obtaining the exact density distribution within the human body from X-ray projections. One approach that has been taken to solve this problem consists of translating the available information into a system of linear inequalities. The size and the sparsity of the resulting system of inequalities (typically, 25,000 inequalities with less than 1% of the coefficients nonzero) makes methods using successive relaxations computationally attractive. A variety of such methods have been proposed with differing relaxation parameters.

A HTTP cookie covert channel

This paper presents a new covert channel based on Google Analytic web cookies in HTTP protocol. The new covert channel is difficult to disrupt and is capable of reasonably high bandwidths. The Google Analytic framework is used by over half of the most popular web sites currently on the Internet; its ubiquitousness across the web implies a great impact of this covert.

A Covert Channel in RTP Protocol

A new covert channel over the RTP protocol is designed and implemented by modifying the timestamp value in the RTP header. Due to the high frequency of RTP packets, the covert channel has a high bit-rate, theoretically up to 350 bps. The broad use of RTP for multimedia applications such as VoIP, provides abundant opportunities to such a covert channel to exist. By using the RTP header, many of the challenges present for covert channels using the RTP payload are avoided. A reference implementation of this covert channel is presented. Bit-rates of up to 325 bps were observed. The channel is very difficult to detect due to expected variations in the timestamp field and the flexible nature of RTP.

ICMP Covert Channel Resiliency

The ICMP protocol has been widely used and accepted as a covert channel. While the ICMP protocol is very simple to use, modern security approaches such as Firewalls, deep-packet inspection and intrusion detection systems threaten the use of ICMP for a reliable means for a covert channel. This study explores the modern usefulness of ICMP with typical security measures in place. Existing ICMP covert channel solutions are examined for compliance with standard RFCs and resiliency with modern security approaches.

NetDev: an object-oriented framework enabling network programming for students and researchers

Pursuing network programming requires breaking through the barrier that most operating systems present at the transport layer. The reasons for the existence of this barrier are both security and convenience. The data link and network layers provide services such as address resolution and routing to the end user. In addition, users programming at these layers can easily spoof addresses, presenting a security risk.For the teacher and researcher, this barrier quickly becomes problematic. Networking students are familiar with the concepts at the lower layers and have a natural curiosity about the software that operates at those layers. Research into lower layer protocols necessitates pealing away the existing layers to replace them with experimental software. Implementing security software depends upon being able to intercept and sometimes inject packets at a low level in the hierarchy.An object-oriented framework for pursuing network programming at all layers above layer 1 is presented. This framework is realized as an open source project[5], providing an object-oriented class library that allows capturing packets at the lowest layers and injecting arbitrary packets into the network. It also includes a library of classes to model various protocol headers. Each class in this library includes the ability to parse a captured packet as well as build a packet from its component fields. This package has been implemented both in Java, using the JNI [14], and in C++.Uses for this framework are discussed, including a summary of a two M.S. projects that have been completed. Current work includes the development of ARP caching and basic routing table maintenance and manipulation. In addition, a number of packet editors exist that allow students to hand-craft packets for injection into the network. Future areas of exploration are outlined.

Covert Channel Using Man-in-the-Middle over HTTPS

The goal of this covert channel is to prove the feasibility of using encrypted HTTPS traffic to carry a covert channel. The encryption key is not needed because the original HTTPS payload is not decrypted. The covert message will be appended to the HTTPS data field. The receiver will extract the covert channel and restore the original HTTPS traffic for forwarding. Only legitimate HTTPS connections will be used as the overt channel. A Man-in-the-Middle (MITM) attack at the sending and receiving ends will give access to modify the traffic streams. The HTTPS return traffic from the server can carry a covert channel. Without the original HTTPS traffic for comparison or the original encryption keys, this covert channel is undetectable.

Across the wire: Teaching software engineering at a distance

There is growing experience with teaching technical topics at a distance. From this experience educators and purchasers of distance courses have derived a large number of questions and concerns. Among these are questions regarding the quality of instruction provided using a particular technology, the importance of real-time interaction, and the authentication of work performed by students whom the instructor never meets face-to-face.

SIGNUM a spectrum of mathematical software considerations—1975 (Paper Session)

In this session, mathematical software developments are considered which range across the spectrum of computer technologies available in 1975. At one end of the spectrum algorithm development for scientific pocket calculators is presented. At the extreme other end of the spectrum the impact on mathematical software development of advanced systems like the Control Data Corporation STAR-100 and the Texas Instruments, Inc. Advanced scientific Computer (ASC) is discussed. Concomitant with the latter end of the spectrum, an algorithm for solving large systems of inequalities is developed. More towards the conventional middle of this spectrum, some new developments in solving (1) initial value problems for ordinary differential equations and (2) constrained nonlinear optimization problems are discussed.