The Attribute-Based Encryption Scheme

The Identity-Based Encryption (IBE) has become an active hotspot in the field of public key cryptography, as it can decrease the cost of using certificates. Recently in order to realize the application of IBE, extending the conception of identity and describing the structure of identity is one of the important works in the study of IBE. For example, there are hierarchical identities, fuzzy identities and identities of attributes as main extension of identity. In the Identity-Based Encryption each user is identified by a unique identity string which was used as the public key of user. In the Attribute-Based Encryption scheme (ABE), each user is identified by a set of attributes, and some function of these attributes is used to determine the limits of decryption of ciphertext. There are many applications of ABE in fuzzy encryption and broadcast encryption.In this paper, we improve the scheme of Qiang Tang and Donyao Ji by using the large universe construction of Sahai and Waters and construct a new verifiable Attribute-Based Encryption scheme, which allows us to apply a collision resistant hash function and use arbitrary strings as attributes. According to the idea of encryption in hierarchical structure, we design the delegation of the keys to alleviate the heavy burden of the private key generation. At the same time, we consider the public verification of ciphertext that can save time when error appears. At last, we analyze the security of the scheme.