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This book explains compactly, without theoretical superstructure and with as little mathematical formalism as possible, the essential concepts in the encryption of messages and data worthy of protection. The focus is on the description of the historically and practically important cipher, signature and authentication methods. Both symmetric encryption and public-key ciphers are discussed. In each case, the strategies used to attack and attempt to "crack" encryption are also discussed. Special emphasis is placed on the practical use of ciphers, especially in the everyday environment. The book is suitable for working groups at STEM schools and STEM teacher training, for introductory courses at universities as well as for interested students and adults.
Have you ever wondered whether mobile phones can be used to confide even the most secret secrets? Or whether online banking is really secure these days? Or whether an electronic signature on contracts sent by e-mail meets legal requirements? All of this has something to do with the encryption – or ciphering – of data, which is sent or stored on data carriers every day in large and ever-increasing quantities via data highways or “wireless”.
Textbooks and reference books take a more scientific approach to the topic of data encryption under the title of cryptography. They deal with the mathematical theories of the common procedures, describe their algorithms and program-technical realizations, and also deal with many topics of the organizational implementation. As a basis for lectures or seminars, it must in the first instance be the goal to introduce students to scientific work and to introduce them to areas of current research. Practitioners working in the subject also need a correspondingly comprehensive presentation. On the other hand, there are also numerous popular science publications that aim at a generally understandable level. This works very well in this case, since simple ciphering methods can easily be brought to the attention of interested laymen and can be substantiated with examples from everyday practice. The mathematics behind it, however, usually remains hidden.
This book aims to be a balancing act between the two. It is a fact that cryptography can be understood quite comprehensively with very little mathematics. Our goal is therefore, without a theoretical superstructure, to deal specifically with the most important procedures of encryption, signing and authentication, and to present them in a compact and mathematically understandable manner, which is reflected in many practical examples.
The Internet with HTTPS is perhaps the most prominent modern application for secure data transmission, but wireless WLAN networks and the Bluetooth radio interface are also well protected today. The PGP Pretty Good Privacy method is widely used for e-mails, while mobile communications with GSM are only partially secure against eavesdropping, but those with UMTS/LTE are much more secure. Another focus is on online banking, credit cards and Bitcoins. Finally, e-passports with their biometric data are also designed to be forgery-proof. Last but not least, data stored on hard disks, and thus passwords in particular, must be protected against unauthorized access.
The target audience for this book is basically anyone who is enthusiastic about the topic in particular, it is also intended as an introduction to more advanced literature. We will have to do relatively little, but nevertheless some mathematics. We will need arithmetic with binary numbers (bits) and with remainders modulo a natural number, as well as an understanding of permutations, both for the conceptual background and for one or the other formal derivations. However, we will build this up piece by piece, with special emphasis on the plausibility of the relationships. So, let’s plunge into the adventure – and have fun.
Basics and History
Symmetric Ciphers
Public-Key Ciphers
Digital Signature