Updatable encryption allows a client to outsource ciphertexts to some untrusted server and periodically rotate the encryption key by sending an update token, where this token should not reveal anything about keys or plaintext. We provide a new and extremely efficient updatable encryption scheme, which we call SHINE, where ciphertext generation consists of applying one permutation and one exponentiation (per message block), and updating ciphertexts requires just one exponentiation. We give a new security notion for updatable encryption schemes that implies prior notions (for schemes with randomized and deterministic updates), and prove that SHINE – and the previous best scheme, RISE – are secure under our new definition.
Gareth T. Davies completed his PhD at the University of Bristol in 2015 under the supervision of Martijn Stam and Bogdan Warinschi. After completing a short postdoc with Prof. Nigel Smart, he became a postdoc in the applied cryptography group at NTNU Trondheim with Colin Boyd and Kristian Gjøsteen. Recently he moved to Universität Paderborn and became a member in the IT-Security group of Prof. Tibor Jager.
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