This publication is intended to help students studying "Fundamentals of Cryptography" and "Fundamentals of Public Key Cryptography" in their specialties. The manual will also be useful for self-study of cryptography and all those who are interested in its practical applications. When writing this manual, the latest published scientific results in the field of cryptography were used, and the experience of teaching similar courses at domestic and foreign universities was also taken into account. To understand the main content of this manual, it is enough to know the basics of probability theory in the scope of the technical university program.