Theoretic Numerical Methods in Cryptography . The RSA cryptographic system, written by a team of authors, is a fascinating and in-depth study of one of the most significant areas in the field of cryptography. This work not only immerses the reader in the world of theoretical bases of numbers and their application in cryptographic systems, but also reveals the practical aspects that make RSA one of the most popular and reliable encryption systems in the modern digital world. From the first pages, the book captures the reader's attention, offering him a unique opportunity to understand how mathematical concepts, such as prime numbers, factorization, and algorithms, underlie information protection. The authors share their knowledge and experience, explaining complex theories in accessible language, which makes the material understandable for both students and professionals in the field of information security. If you are interested in how cryptography works, and want to learn about data protection methods, this work will be a real discovery for you. The book will be especially interesting for students and graduate students of technical specialties, as well as specialists in the field of information technology and cybersecurity .. It will suit both those who are just beginning their acquaintance with cryptography, and those who already have certain knowledge and want to deepen their skills. Readers interested in mathematics, number theory and their practical application will find in this book a lot of useful information and inspiration. The topics raised in the book are diverse and relevant. The authors consider not only theoretical aspects, but also practical applications of the cryptographic system RSA, which is used to protect data on the Internet, electronic payments and other areas. The book also addresses security issues, vulnerabilities, and methods of attacking cryptographic systems, making it an important source of knowledge for anyone who wants to be aware of modern cybersecurity threats. The style of the authors is distinguished by clarity and logical presentation, which allows the reader to easily follow the course of thought and assimilate complex concepts. The book is filled with examples, illustrations and tasks that help to consolidate the knowledge gained . The authors strive to make the material not only informative, but also fascinating, which makes reading a real pleasure. If you are looking for literature that will help you understand the basics of cryptography and number theory, pay attention to other well-known works in this field, such as “Cryptology and data security” or “