In these early decades of the information age, the flow of information is becoming more and more central to our daily lives. It has therefore become important that information transmission be protected against eavesdropping (as, for example, when one sends credit card information over the Internet) and against noise (which might occur in a cell phone transmission, or when a compact disk is accidentally scratched). Though most of us depend on schemes that protect information in these ways, most of us also have a rather limited understanding of how this protection is done. Part of the aim of this book is to introduce the basic concepts underlying this endeavor.

Besides its practical significance, it happens that the subject of protecting information is intimately related to a number of central ideas in mathematics and computer science, and also, perhaps surprisingly, in physics. Thus in addition to its significance for society, the subject provides an ideal context for bringing ideas from these disciplines together. This interdisciplinarity is part of what has attracted us to the subject, and we hope it will appeal to the reader as well.

Among undergraduate texts on coding or cryptography, this book is unusual in its inclusion of quantum physics and the emerging technology of quantum information. Quantum cryptography, in which an eavesdropper is detected by his or her unavoidable disturbance of delicate quantum signals, was proposed in the 1980s and since then has been investigated and developed in a number of laboratories around the world.