Research On Hierarchical Attribute Based Encryption Schemes

Identity based encryption(IBE) allows a sender to encrypt a message using only the identity of the recipient as a public key. This resolves the problem that when the number of users increases, key distribution and management will become a constrained problem. Now, with the rapid development of science and technology, quantum computing may be eventually coming. But most schemes at present couldn't resist quantum attacks. Hence, the construction of an IBE scheme with high efficiency and post quantum security is very necessary.Attribute based encryption(ABE) can support one-to-many encryption mechanism, but in cloud environment, the number of users increased, traditional ABE would produce serious burden in key distribution and management. In addition, the user is often in a hierarchical environment, where their properties have a certain hierarchy. The emergence of the hierarchical attribute based encryption(HABE) can solve such problems well. In the cloud storage and distribution, how to design an efficient and secure HABE scheme is very valuable.Based on the motivations of the above, we give the main points of this thesis as follows:1. A new IBE scheme based on a lattice is introduced. To overcome the shortcomings in the existing works such as fast extension of private keys space and large size of public keys, a new technique is introduced to generate a short lattice basis. It results in a new IBE in a fixed dimension lattice, where it delegates the short basis but keep the lattice dimension unchanged. The new scheme has constant size ciphertexts since it consists of two group elements. It achieves the full security which is a strong security for the IBE system. In the standard model, the security of proposed scheme is reduced to the LWE problem. In addition, the scheme can be extended to the hierarchical identity based encryption(HIBE). It maintains the same secure feature with the proposed IBE, and its security is reduced to the LWE problem.2. A new HABE scheme is proposed. The proposed scheme combines the ciphertext-policy attribute based encryption scheme with HIBE, which issues a ciphertext-policy hierarchical attribute-based encryption. Both the main domain authorization and users achieve hierarchical under the fine-grained access control. In addition, the proposed scheme inherits flexibility and achieves scalability with short ciphertexts. A user is allowed to delegate to its subordinates without worrying whether the subordinates' attribute sets are subsets or not. Under three static assumptions instead of other strong assumptions, it also achieves full security in the standard model.