Fuzzy Identity Based Encryption with a flexible threshold value

In recent years, the problem of online data and information security has been increasingly serious and prevalent. Security issues are resolved via cryptography. Access control over the encrypted messages is necessary for some applications, therefore message encryption cannot simply achieve the stated aims. To achieve these requirements, attribute-based encryption (ABE) is used. This type of encryption provides both security and access structure for the network users simultaneously. Fuzzy Identity-Based Encryption (FIBE) is a special mode of ABE that provides a threshold access structure for the users. This threshold value is set by the authority for users, which is always fixed and cannot be changed. So, the sender (encryptor) will not play a role in determining the threshold value. The mentioned issue exists also in Key Policy Attribute Based Encryption (KP-ABE) schemes. In this paper, we present a FIBE scheme in addition to the authority, the sender also plays a role in determining the threshold value. Thus, the policy will be more flexible than previous FIBE schemes in that the threshold value is selected only by the authority. We can call the proposed scheme a dual-policy ABE. The proposed technique for flexibility of threshold value can be applied in most of exist KP-ABE schemes. We use the (indistinguishable) selective security model for a security proof. The hardness assumption that we use is the modified bilinear decision Diffie-Hellman problem.