Quantum theory has found a new field of applications in the realm of information and computation during the recent years. This paper reviews how quantum physics allows information coding in classically unexpected and subtle nonlocal ways, as well as information processing with an efficiency largely surpassing that of the present and foreseeable classical computers. Some outstanding aspects of classical and quantum information theory will be addressed here. Quantum teleportation, dense coding, and quantum cryptography are discussed as a few samples of the impact of quanta in the transmission of information. Quantum logic gates and quantum algorithms are also discussed as instances of the improvement in information processing by a quantum computer. We provide finally some examples of current experimental

We consider the problem of establishing jam-resistant, wireless, omnidirectional communication channels when there is no initial shared secret. No existing system achieves this. We propose a general algorithm for this problem, the BBC algorithm, and give several instantiations of it. We develop and analyze this algorithm within the framework of a new type of code, concurrent codes, which are those superimposed codes that allow efficient decoding. Finally, we propose the Universal Concurrent Code algorithm, and prove that it covers all possible concurrent codes, and give connections between its theory and that of monotone Boolean functions.

The invention of public-key cryptography led to the notion that cryptographically protected messages could be used as evidence to convince an impartial adjudicator that a disputed event had in fact occurred. Information stored in a computer is easily modi ed, and so records can be falsi ed or retrospectively modi ed. Cryptographic protection prevents modi cation, and it is hoped that this will make cryptographically protected data acceptable as evidence. This usage of cryptography to render an event undeniable has become known as non-repudiation. This dissertation is an enquiry into the fundamental limitations of this application of cryptography, and the disadvantages of the techniques which are currently in use. In the course of this investigation I consider the converse problem, of ensuring that an instance of communication between computer systems leaves behind no unequivocal evidence of its having taken place. Features of communications protocols that were seen as defects from the standpoint of non-repudiation can be seen as bene ts from the standpoint of this converse problem, which I call \plausible deniability". i Declaration This dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration. This dissertation is not substantially the same as any other that I have submitted for a degree, diploma, or other quali cation at any other university. Acknowledgements Iwould like to thank Peter Kirstein and Ben Bacarisse for managing the research projects which caused me to become interested in this area; Steve Kent for many interesting discussions about the problems of key certi cation; Russ Housley for suggesting the term \plausible deniability"; Roger Needham for being my supervisor; and Bruce Christianson for his advice on how to write a dissertation. ii To my grandfather,

Traditionally, omnidirectional, radio frequency (RF) communication has been made resistant to jamming by the use of a secret key that is shared by the sender and receiver. There are no known methods for achieving jam resistance without that shared key. Unfortunately, wireless communication is now reaching a scale and a level of importance where such secret-key systems are becoming impractical. For example, the civilian side of the Global Positioning System (GPS) cannot use a shared secret, since that secret would have to be given to all 6.5 billion potential users, and so would no longer be secret. So civilian GPS cannot currently be protected from jamming. But the FAA has stated that the civilian airline industry will transition to using GPS for all navigational aids, even during landings. A terrorist with a simple jamming system could wreak havoc at a major airport. No existing system can solve this problem, and the problem itself has not even been widely discussed. The problem of keyless jam resistance is important. There is a great need for a system that can broadcast messages without any prior secret shared between the sender and receiver. We propose the first system for keyless jam resistance: the BBC algorithm. We describe the encoding, decoding, and broadcast algorithms. We then analyze it for expected resistance to jamming and error rates. We show that BBC can achieve the same level of jam resistance as traditional spread spectrum systems, at just under half the bit rate, and with no shared secret. Furthermore, a hybrid system can achieve the same average bit rate as traditional systems. I.

Current solutions for providing communication security in network applications allow customization of certain security attributes and techniques, but in limited ways and without the benefit of a single unifying framework. Here, the design of a highly-customizable extensible service called SecComm is described in which attributes such as authenticity, privacy, integrity, and non-repudiation can be customized in arbitrary ways. With SecComm, applications can open secure communication connections in which only those attributes selected from among a wide range of possibilities are enforced, and are enforced using the strength or technique desired. SecComm has been implemented using Cactus, a system for building configurable communication services. In Cactus, different properties and techniques are implemented as software modules called micro-protocols that interact using an event-driven execution paradigm. This non-hierarchical design approach has a high degree of flexibility, ye...

Distribution A, Approved for public release, distribution unlimited Abstract. We consider the problem of establishing jam-resistant, wireless, omnidirectional communication channels when there is no initial shared secret. No existing system achieves this. We propose a general algorithm for this problem, the BBC algorithm, and give several instantiations of it. We develop and analyze this algorithm within the framework of a new type of code, concurrent codes, which are those superimposed codes that allow efficient decoding. Finally, we propose the Universal Concurrent Code algorithm, and prove that it covers all possible concurrent codes, and give connections between its theory and that of monotone Boolean functions.

All cryptosystems currently m use are symmetrm m the sense that they require the transmitter and receiver to share, m secret, either the same pmce of reformation (key) or one of a paLr of related keys easdy computed from each other, the key is used m the encryption process to introduce uncertainty to an unauthorized receiver. Not only is an

This paper examines the practical utility of RSA encryption as a means of securing data. Recent announcements over the past ten years concerning the breaking of RSA encryption keys have raised doubts about the security of RSA encryption. After all, the scientists who came up with RSA initially claimed that such keys would take millions of years to break. Our analysis of this topic is divided into two large headings: the history of Cryptography and RSA. The history of cryptography demonstrates the cryptography is always improving as a result of pressure by cryptanalyst techniques. Once a flaw in a technique is uncovered, the cryptography changes to accommodate the flaw and make itself more secure. RSA did not come from nothingness, but rather a series of cryptographic exploits that have evolved into the cryptography goliath that exists today. In examining, the ways that other techniques have failed in the past, we are also demonstrating the ways that RSA has improved upon those flaws. The second half of the paper analyzes RSA cryptography in depth both its algorithm and its implementations. RSA can be subverted and there are alternate cryptographic techniques, but ultimately RSA remains the most ideal form of cryptography to date and in the foreseeable future. Thesis: Throughout history, there has been a constant battle between the cryptographers that encrypt and the cryptanalyst that break the encryption. Recently, there have been a series of findings concerning flaws and security leaks in implementations of RSA encryption. Coupled with the latest news concerning the breaking of a higher numbered RSA encryption key, the credibility of RSA has been called into question. However, RSA 2 represents an extraordinarily secure encryption scheme that is not threatened by many forms of subversion. With careful attention, RSA still represents a nearly unbreakable cryptographic scheme that has come as a direct result centuries of cryptographic evolution. 1.

<F1.176e+04> Information is now the most valuable resource in the world. Whether it is a personal letter or an industrial secret, all information has a worth to someone. This thesis considers issues of security and privacy for such information. It discusses the reasons for wishing to protect data and the methods available for doing so. Specifically, the project concerns cryptography and secure communications, in particular the Secure Sockets Layer (SSL) protocol. It contains a communications and security analysis of SSL as well as details of the construction of a secure reference implementation of the protocol. iii iv<F6.421e+04> We have it in our power to begin the world over again <F3.971e+04>Declaration<F1.176e+04> All the work contained within this thesis, except where otherwise acknowledged, was solely the effort of the author. At no stage was any collaboration entered into with any other party. Any views expressed within or implied by the dissertation are those of the author...

As a contribution to IEEE P1363a, we propose a provably secure digital signature algorithm called the Korean Certificate-based Digital Signature Algorithm (KCDSA, in short) and its elliptic curve variant (EC-KCDSA). We believe that the proposed signature schemes are more advantageous than DSA/EC-DSA in both security and efficiency. No patent related with KCDSA/EC-KCDSA has been submitted, and there are no known limitation and disadvantage. This paper describes these signature algorithms and discusses their security and efficiency aspects. 1 Introduction The digital signature technique, a technique for signing and verifying digital documents in an unforgeable way, is essential for secure transactions over open networks. Digital signatures can be used in a variety of applications to ensure the integrity of data exchanged or stored and to prove to the recipient the originator's identity. The security of most public key cryptosystems widely used in practice is based on two difficu...