ABSTRACT
In comparison to symmetric key cryptosystem, public key cryptosystem is slower and requires a longer key, but it simplifies key distribution problem. Security of any public key cryptosystem is based on some assumptions. The security of Diffie-Hellman key exchange protocol is based on the computational Diffie-Hellman assumption. One of the basic security criteria for a public key cryptosystem is that the system should be randomized. The concept of Optimal Asymmetric Encryption Padding/Protocol was introduced by Bellare and Rogaway in 1994 to achieve these criteria. Public key algorithm is commonly used for the hybrid schemes: public key system for key distribution and symmetric key system for encryption of the message. In 1978, Rivest, Shamir, and Adleman introduced the practical and the most popular public-key cryptosystem, the so-called Rivest–Shamir–Adleman (RSA) cryptosystem. Due to productive properties of RSA cryptosystem, the Meet-in-the-middle attack was proposed by Boneh, Joux and Nguyen under certain conditions.
