You are looking at a specific version 20210916:021712 of this paper. See the latest version.

Paper 2021/221

The Direction of Updatable Encryption Does Matter

Ryo Nishimaki

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).

Note: The presentation was improved. (9/16/2021)

Metadata
Available format(s)
PDF
Category
Public-key cryptography
Publication info
Preprint. MINOR revision.
Keywords
updatable encryptionkey updatelattice
Contact author(s)
ryo nishimaki zk @ hco ntt co jp
History
2021-12-21: last of 7 revisions
2021-03-02: received
See all versions
Short URL
https://ia.cr/2021/221
License
Creative Commons Attribution
CC BY
Note: In order to protect the privacy of readers, eprint.iacr.org does not use cookies or embedded third party content.