Cryptanalysis and Improvement to Two Key-Policy Attribute-Based Encryption Schemes for Weighted Threshold Gates

Attribute-based encryption is one of the most suitable access control mechanism for modern data sharing models. To provide better performance, lots of attribute-based encryption schemes are constructed over without pairings. However, these schemes are either with no security proofs or broken. In this manuscript, we give the cryptanalysis of two key-policy attribute-based encryption schemes for weighted threshold gates. We propose two attack methods, the first one is able to generate valid private keys without the master secret keys, and the second one is able to recover the master secret key when an attacker gathers enough number of private keys. Moreover, an improved schemes is given in this manuscript. We also present a security analysis to show that our improved scheme fix the security flaws with only one pairing added.