Enabling cloud storage auditing with key-exposure resilience under continual key-leakage

Cloud storage auditing is a service that is usually provided to enable clients to verify the integrity of their data stored in the cloud. However, clients risk exposing their secret key. To address the problem of key exposure, researchers have provided "Forward Security" by dividing the entire lifetime of the secret key into several periods and updating the secret key within each of these periods. Forward security can ensure the validity of authenticators before the period in which the secret key is fully exposed. However, the security of these protocols can be broken by launching side-channel attacks to leak the secret key partially rather than fully. In this study, we focus on implementing measures in cloud storage auditing to protect against side-channel attacks in practice. We formalize the definition and security model of a cloud storage auditing protocol, which supports forward security under continual key-leakage, and construct the first protocol. Our protocol remains secure even if an adversary obtains partial leakage of the secret key during a period. In addition, if the secret key were to be fully disclosed in a certain period, our protocol would maintain forward security. Therefore, the proposed protocol provides stronger security compared with existing protocols. (c) 2020 Elsevier Inc. All rights reserved.