注：本文加解密算法构建完全参考经典ABE paper:
Attribute-Based Encryption for Fine-Grained Access Control of Encrypted Data。
一.ABE介绍
ABE算法有两种类型，KP-ABE(Key-Policy Attribute-based encryption)和CP-ABE(Ciphertext-policy Attribute-based encryption)。从名字就可以看出
CP-ABE 密文与 A c c e s s T r e e Access Tree Acc
