This lecture covers the Chinese Remainders Theorem, RSA public-key cryptosystem, and related concepts. It explains the construction used in the proof of Lagrange's Theorem, the bijective properties of the Chinese Remainders map, and the isomorphism with respect to addition and multiplication. The lecture also delves into the proof of Fermat's Theorem, Euler's Theorem, and the application of Chinese Remainders in combining prime numbers. It concludes with the generation of RSA keys, encryption, and decryption processes, illustrating how RSA works with a practical example.