  For better data availability and accessibility while ensuring data secrecy,
organizations often tend to outsource their encrypted data to the cloud storage
servers, thus bringing the challenge of keyword search over encrypted data. In
this paper, we propose a novel authorized keyword search scheme using
Role-Based Encryption (RBE) technique in a cloud environment. The contributions
of this paper are multi-fold. First, it presents a keyword search scheme which
enables only the authorized users, having proper assigned roles, to delegate
keyword-based data search capabilities over encrypted data to the cloud
providers without disclosing any sensitive information. Second, it supports a
multi-organization cloud environment, where the users can be associated with
more than one organization. Third, the proposed scheme provides efficient
decryption, conjunctive keyword search and revocation mechanisms. Fourth, the
proposed scheme outsources expensive cryptographic operations in decryption to
the cloud in a secure manner. Fifth, we have provided a formal security
analysis to prove that the proposed scheme is semantically secure against
Chosen Plaintext and Chosen Keyword Attacks. Finally, our performance analysis
shows that the proposed scheme is suitable for practical applications.
