For data storage outsourcing services, it is important to allow data owners to efficiently and securely verify that the storage sever stores their data correctly. To address this issue, several proof-of-retrievability(POR) schemes have been proposed wherein a storage sever must prove to a verifier that all of a client\'s data is stored correctly. While existing POR schemes offer decent solutions addressing various practical issues, they either have a non-trivial (linear or quadratic) communication complexity, or only support private verication - only the data owner can verify the remotely stored data. It remains open to design a POR scheme that achieves both public verifiability and constant communication cost simultaneously.
In this paper, we solve this open problem and propose the first POR scheme with public verifiability and constant communication cost. In our proposed scheme, the message exchanged between the prover and verifier is composed of a const number of the underlying group elements. Different from existing private POR construction, our scheme allows public verification and releases the data owners from burden of being staying online. Thorough analysis and experiments on Amazon S3 show that our proposed scheme is efficient and practical. We prove the security of our scheme based on Computational Diffie-Hellman Assumption, Strong Diffie-Hellman Assumption and Bilinear Strong Diffie-Hellman Assumption.