RSA is a public-key cryptographic system, and is the most famous and widely-used cryptographic system in today's digital world. This professional book covers almost all known cryptanalytic attacks and defenses of the RSA cryptographic system and its variants. It is the first book available that covers its subject exclusively. Since RSA depends heavily on computational complexity theory and number theory, background information on complexity theory and number theory is presented first, followed by an account of the RSA cryptographic system and its variants. This book is also suitable as a secondary text for advanced-level students in computer science and mathematics.