Symmetric-Key Based Proofs of Retrievability Supporting Public Verification
Proofs-of-Retrievability enables a client to store his data on a cloud server so that he executes an efficient auditing protocol to check that the server possesses all of his data in the future. During an audit, the server must maintain full knowledge of
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Department of Computer Science and Engineering, University at Buffalo, Buffalo, USA {chaoweng,kuiren}@buffalo.edu, [email protected] 2 School of Information Science and Technology, Sun Yat-sen University, Guangzhou, China 3 Guangdong Key Laboratory of Information Security Technology, Guangzhou, China 4 SAP, Karlsruhe, Germany [email protected] 5 College of Information Engineering, Qingdao University, Qingdao, China Abstract. Proofs-of-Retrievability enables a client to store his data on a cloud server so that he executes an efficient auditing protocol to check that the server possesses all of his data in the future. During an audit, the server must maintain full knowledge of the client’s data to pass, even though only a few blocks of the data need to be accessed. Since the first work by Juels and Kaliski, many PoR schemes have been proposed and some of them can support dynamic updates. However, all the existing works that achieve public verifiability are built upon traditional publickey cryptosystems which imposes a relatively high computational burden on low-power clients (e.g., mobile devices). In this work we explore indistinguishability obfuscation for building a Proof-of-Retrievability scheme that provides public verification while the encryption is based on symmetric key primitives. The resulting scheme offers light-weight storing and proving at the expense of longer verification. This could be useful in apations where outsourcing files is usually done by low-power client and verifications can be done by well equipped machines (e.g., a third party server). We also show that the proposed scheme can support dynamic updates. At last, for better assessing our proposed scheme, we give a performance analysis of our scheme and a comparison with several other existing schemes which demonstrates that our scheme achieves better performance on the data owner side and the server side. Keywords: Cloud storage ity obfuscation
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· Proofs of retrievability · Indistinguishabil-
Introduction
Nowadays, storage outsourcing (e.g., Google Drive, Dropbox, etc.) is becoming increasingly popular as one of the applications of cloud computing. It enables c Springer International Publishing Switzerland 2015 G. Pernul et al. (Eds.): ESORICS 2015, Part I, LNCS 9326, pp. 203–223, 2015. DOI: 10.1007/978-3-319-24174-6 11
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clients to access the outsourced data flexibly from any location. However, the storage provider (i.e., server) is not necessarily trusted. This situation gives rise to a need that a data owner (i.e., client) can efficiently verify that the server indeed stores the entire data. More precisely, a client can run an efficient audit protocol with the untrusted server where the server can pass the audit only if it maintains knowledge of the client’s entire outsourced data. Formally, this implies two guarantees that the client wants from the server: Authenticity and Retrievability. Authenticity ensures that the client can verify the correctness of the data fetched from the server. On the other hand, Ret
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