  Attribute-based encryption (ABE) is a promising tool for implementing
fine-grained access control.To solve the matters of security in single
authority, access policy public, not traceable of malicious user,we proposed a
scheme of multi-authority. Moreover, multi-authority may bring about the
collusion of different authorities.In order to solve these problem,we proposed
a scheme of access tree structure with policy hidden and access complex.Once
the private key is leaked, our scheme can extract the user ID and find it.If
the authorities share their information with each other,the scheme avoid them
to combine together to compute the key information and decrypt the
ciphertext.Finally,the scheme proved to be secure under selective-set of
IND-CPA.
