An accountable authority attribute-based encryption （A-ABE） scheme is presented in this paper. The notion of accountable authority identity-based encryption （A-IBE） was first introduced by Goyal at Crypto＇07. It is a novel approach to mitigate the （inherent） key escrow problem in identity-based cryptosystems. In this work, the concept of accountable authority to attribute-based encryption （ABE） setting is generalized for the first time, and then a construction is given. The scheme non-trivially integrates an A-IBE scheme proposed by Libert et al. with an ABE scheme. In our construction, a user will be identified by a pair （ id, o~）, where id denotes the user＇ s identity and ω denotes the set of attributes associated to the user. In addition, our construction is shown to be secure under some reasonable assumptions.
Due to the compromise of the security of the underlying system or machine stonng the key, exposure of the private key can be a devastating attack on a cryptosystem. Key insulation is an important technique to protect private keys. To deal with the private （signing） key exposure problem in identity-based signature systems, we propose an identity-based threshold key-insulated signature （IBTKIS） scheme. It strengthens the security and flexibility of existing identity-based key-insulated signature schemes. Our scheme＇ s security is proven in the random oracle model and rests on the hardness of the computational Diffie-Helhnan problem in groups equipped with a pairing. To the best of our knowledge, it is the first IBTKIS scheme up to now.
