Preface

Cryptography is an ancient science. According to Svetonio, more than 2000 years ago Julius Caesar encrypted his messages by shifting the alphabet by three positions, using what is today known as the *Caesar cipher* (Mary Stuart also used it). After 2000 years, we know much more about cryptography and cryptanalysis, and no one would use the Caesar cipher anymore (although it experienced a rebirth with the ROT13 masking procedure in the Usenet newsgroup); much more secure and diverse algorithms have been designed. The cryptography toolbox nowadays includes not only encryption algorithms but also hash functions, signature protocols, zero-knowledge proofs, homomorphic encryption procedures, poker-byphone protocols, and more.

Nevertheless, despite 2000 years of history, cryptography research is still very active, pursuing solutions to several interesting (and difficult) problems such as identity-based cryptography, fully (and practical) homomorphic encryption, physically unclonable functions (for hardware authentication), cryptography based on quantum mechanics (e.g., key distribution via entanglement), and cryptography robust against quantum computers.

Research in cryptography is expected to maintain its momentum in the future too, fueled by the still-increasing computational power and new needs like privacy and the Internet of Things (IoT).

This book is a snapshot of some recent results in this active field of research. It discusses quantum cryptography and quantum key distribution; lightweight protocols suited, for example, for the IoT; physical unclonable functions in the specific application of RFID systems; and security protocols based on optical approach.

Cryptography does not only study how to hide information but it also studies how to recover encrypted information. This is cryptanalysis, the other side of cryptography, which is as important as cryptography itself. This book gives space to cryptanalysis as well, analyzing the security of cryptosystems based on error correction codes, discussing tradeoff attacks for symmetric ciphers, and analyzing hybrid encryption models.

This book is not meant to be the final word on cryptography and cryptanalysis. It is designed to provide readers with useful tools and spark new research ideas

> **Riccardo Bernardini** University of Udine – DPIA, Udine, Italy

Section 1

New Techniques

**1**
