### State-free End-to-End Encrypted Storage and Chat Systems based on Searchable Encryption

Keita Emura, Ryoma Ito, Sachiko Kanamori, Ryo Nojima, and Yohei Watanabe

##### Abstract

Searchable symmetric encryption (SSE) has attracted significant attention because it can prevent data leakage from external devices, e.g., clouds. SSE appears to be effective to construct such a secure system; however, it is not trivial to construct such a system from SSE in practice because other parts must be designed, e.g., user login management, defining the keyword space, and sharing secret keys among multiples users who usually do not have public key certificates. In this paper, we describe the implementation of two systems from the state-free dynamic SSE (DSSE) (Watanabe et al., ePrint 2021), i.e., a secure storage system (for a single user) and a chat system (for multiple users). In addition to the DSSE protocol, we employ a secure multipath key exchange (SMKEX) protocol (Costea et al., CCS 2018), which is secure against some classes of unsynchronized active attackers. It allows the chat system users without certificates to share a secret key of the DSSE protocol in a secure manner. To realize end-to-end encryption, the shared key must be kept secret; thus, we must consider how to preserve the secret on, for example, a user's local device. However, this requires additional security assumptions, e.g., tamper resistance, and it seems difficult to assume that all users have such devices. Thus, we propose a secure key agreement protocol by combing the SMKEX and login information (password) that does not require an additional tamper-resistant device. Combining the proposed key agreement protocol and the underlying state-free DSSE protocol allow users who know the password to use the systems on multiple devices.

Available format(s)
Category
Cryptographic protocols
Publication info
Preprint. MINOR revision.
Keywords
Dynamic searchable symmetric encryptionSecure multipath key exchangeState freeSecure storageSecure ChatImplementation
Contact author(s)
k-emura @ nict go jp
History
2021-09-13: last of 2 revisions
See all versions
Short URL
https://ia.cr/2021/953

CC BY

BibTeX

@misc{cryptoeprint:2021/953,
author = {Keita Emura and Ryoma Ito and Sachiko Kanamori and Ryo Nojima and Yohei Watanabe},
title = {State-free End-to-End Encrypted Storage and Chat Systems based on Searchable Encryption},
howpublished = {Cryptology ePrint Archive, Paper 2021/953},
year = {2021},
note = {\url{https://eprint.iacr.org/2021/953}},
url = {https://eprint.iacr.org/2021/953}
}

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