| One of most important goals of cryptography is to allow two parties to establish a "secure line" of communication without assuming the existence of a shared secret. This goal is typically achieved by using Public Key Cryptography. In recent years, a new variation of public key cryptography, called Identity Based Encryption (IBE) has emerged. In this thesis we discuss the definitions of chosen ciphertext security for IBE, present a new definition which is reasonable yet strictly stronger than previous ones, and construct an efficient IBE system which is secure in our strong definition. We also review the elegant public key encryption system of Kurosawa and Desmedt and present a new proof of security. |
