In this modern and fast paced electronic world,security plays a key role where viruses, eavesdropping, hackers and electronic fraud are common. Cryptography is an important subject in ensuring privacy and security of information. This book focuses on public key cryptosystems and provided efficient modular multiplication technique for public key cryptosystem. It is meant for research scholars of computer science who aspire to explore new algorithms in Public key cryptography. It is useful for networking professionals and to people who incorporate different cryptographic algorithms.