Reserarch On Hierarchical Identity-Based Encryption Schemes

Because of the applications of the bilinear pairings, IBE system improved rapidly, IBE system gained much production, which has been an active hotspot direction in cryptography field. IBE system decreased the cost of management using ceitificate. However, there are some problems about IBE, such as the key escrow problem, overloaded private key generation and so on. Aiming at these problems, this thesis studied IBE system deeply, which focused on the study of hierarchy of IBE system mainly, the work as follows.At first, the basis condition and the framework of IBE is introduced, IBE based on bilinear pairings which is proposed by Boneh and Franklin(BF-IBE) is analyzed in detail, some variations of BF-IBE scheme are designed to realize the concrete applications in reality.Secondly, aiming at the key escrow problem in IBE scheme, the solutions nowadays is given, such as KPA group authentication, certificates-based and so on. Advantages and disadvantage about the solutions are discussed. A method which users participant in generation of key to solve the key escrow problem is proposed, Through comparing the IBE scheme using new method with other IBE scheme in many ways such as key generation, key escrow, system cost, the new IBE scheme is analysed.Moreover, on the basis of BF-IBE, according to the idea of encryption in hierarchical structure, a more security HIBE is proposed, solving the problem that burden of the private key generation is too heavy in IBE, and security of the scheme is analysed.Finally, the length of ciphertext in identity based hierarchical encryption scheme can be shortened in two conditions, the scheme is improved in the two conditions, two kinds of method that shorten length of ciphertext are proposed,and the scheme is analysed.