Adaptively Secure KP-ABE For Circuits With Fan-In n And Fan-Out 1

The attribute-based encryption (ABE) scheme is suitable for access control of ciphertext in cloud computing. Kowalczyk and Wee proposed an adaptively secure attribute encryption scheme that supports NC1 circuits. However, the circuit depth increases because this scheme supports only circuits with fan-in 2, which increases the key length and computational complexity of the key generation and decryption algorithms. To improve efficiency, we designed a secret sharing scheme for circuits with fan-in n, and we proposed a key-policy ABE scheme that supports circuits with fan-in n. We also designed pebbling rules for secret sharing in circuits with fan-in n, improving the compactness of the security reduction. Finally, we proved the adaptive security of the scheme by using a piecewise guessing framework and dual-system encryption. Compared with existing schemes, our scheme reduces the key size, improves the efficiency of the key generation algorithm and the decryption algorithm and provides tighter security reduction.