"In the era of volatile worldwide growth of electronic data storage and communications, operative protection of information has become a critical necessity. Cryptography is a popular ways of sending vital information in a secret way. The state of present day of information security system includes confidentiality, authenticity, integrity, nonrepudiation. The security of communication is a critical issue on World Wide Web. It is about confidentiality, integrity, authentication through access or editing of confidential internal documents. Cryptography will endure to play significant roles in developing of new security solutions which will be in great demand with the advent of high-speed next-generation communication systems and networks. Cryptography and especially encryption and decryption algorithms are areas where active research keep happening and new ideas keep coming but a very few stand the test of time. We will be touching briefly on some of them and they have been chosen because huge interest has been shown by cryptographic community in them and some organizations have gone ahead in implementing, filed patents and a few enterprises have started using them as well. This book deals with theoretical and fundamental aspects of cryptography, discussing various solicitations of cryptographic protocols and practices in designing computing and network security solutions. It deliberates some of the acute security challenges faced by today's computing world and offers insights to possible mechanisms to defend against these attacks. It will be useful for researchers, engineers, graduate and doctoral students working in cryptography and security related areas. It will also be useful for faculty members of graduate schools and universities."