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Attribute-based encryption (ABE) is a promising cryptographic primitive for fine-grained access control of distributed data. In ciphertext policy attribute-based encryption (CP-ABE), each user is associated with a set of attributes and data are encrypted with access policies on attributes. A user is able to decrypt a ciphertext if and only if his attributes satisfy the access policy embedded in the ciphertext. However, key escrow is inherent in ABE systems. A curious key generation center in that construction has the power to decrypt every ciphertext. We found that most of the existing ABE schemes depending on a single key authority suffer from the key escrow problem. In this study, we propose a novel CP-ABE key issuing architecture that solves the key escrow problem. The proposed scheme separates the power of issuing user keys into two parties: the key generation center and the attribute authority. In the proposed …