Cryptography concerns the principles, protocols, and methods for protecting information against deliberate alteration. For millennia, cryptography was mainly used in diplomacy and military affairs, but cryptographic techniques have recently also been introduced into the bureaucratic, managerial, and economic sides of civil life, and they have been instrumental to the Network (Internet). This book grows from notes of a course in Cryptography given at Turin Polytechnic, and has maintained the same structure, which interleaves basic notions essential to the students with the presentation of the classic cryptographic algorithms, their history, and the analysis of their security.