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Paper: The Direction of Updatable Encryption Does Matter

Authors:
Ryo Nishimaki , NTT Corporation
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Conference: PKC 2022
Abstract: We introduce a new definition for key updates, called backward-leak uni-directional key updates, in updatable encryption (UE). This notion is a variant of uni-directional key updates for UE. We show that existing secure UE schemes in the bi-directional key updates setting are not secure in the backward-leak uni-directional key updates setting. Thus, security in the backward-leak uni-directional key updates setting is strictly stronger than security in the bi-directional key updates setting. This result is in sharp contrast to the equivalence theorem by Jiang (Asiacrypt 2020), which says security in the bi-directional key updates setting is equivalent to security in the existing uni-directional key updates setting. We call the existing uni-directional key updates ``forward-leak uni-directional'' key updates to distinguish two types of uni-directional key updates in this paper. We also present two UE schemes with the following features. - The first scheme is post-quantum secure in the backward-leak uni-directional key updates setting under the learning with errors assumption. - The second scheme is secure in the no-directional key updates setting and based on indistinguishability obfuscation and one-way functions. This result solves the open problem left by Jiang (Asiacrypt 2020).
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BibTeX
@inproceedings{pkc-2022-31698,
  title={The Direction of Updatable Encryption Does Matter},
  publisher={Springer-Verlag},
  author={Ryo Nishimaki},
  year=2022
}