“The Secret Key – Sevil and Teymur’s Adventures in the World of Cryptography” is a digital, educational, and entertaining book specially created for children. In this book, our heroes Sevil and Teymur, following the trail of a mysterious key that accidentally falls into their hands, set off on a journey into the magical world of ancient ciphers, secret codes, and cryptographic secrets. Throughout this adventure, they read different clues, solve logic-based puzzles, learn how to decode encrypted messages, and discover step by step how information is protected. The book not only develops children’s logical thinking, attention, and problem-solving skills, but also introduces them to the basic concepts of cryptography in a simple and engaging way.