Multi-authority attribute-based encryption with honest-but-curious central authority

Abstract

An attribute-based encryption scheme capable of handling multiple authorities was recently proposed by Chase. The scheme is built upon a single-authority attribute-based encryption scheme presented earlier by Sahai and Waters. Chase's construction uses a trusted central authority that is inherently capable of decrypting arbitrary ciphertexts created within the system. We present a multi-authority attribute-based encryption scheme in which only the set of recipients defined by the encrypting party can decrypt a corresponding ciphertext. The central authority is viewed as ‘honest-but-curious’: on the one hand, it honestly follows the protocol, and on the other hand, it is curious to decrypt arbitrary ciphertexts thus violating the intent of the encrypting party. The proposed scheme, which like its predecessors relies on the Bilinear Diffie–Hellman assumption, has a complexity comparable to that of Chase's scheme. We prove that our scheme is secure in the selective ID model and can tolerate an honest-but-curious central authority.

Keywords:

• pairing-based cryptography
• attribute-based encryption

2009 Mathematics Subject Classification :

• 94A60

Notes

We refer to a function as negligible, if .

Here we exploit that ℋ never queries the same authority k twice with the same user u, and that for k≠k′ we have (cf. [Remark 1 5). These assumptions ensure that the validity of does not depend on the future secret key queries of ℋ.