Paper 2024/1941 Original: eprint.iacr.org/2024/1941 ↗
Universally Composable Server-Supported Signatures for Smartphones
Abstract
Smart-ID is a signing and authentication service available to residents of Belgium, Estonia, Iceland, Latvia and Lithuania. Such smartphone-based signing service delivers the usability of software keys with security guarantees of ID-cards by relying on a remote server to compensate for weak device protection. Security of current Smart-ID relies on multi-prime server-supported RSA, password-authenticated key shares and clone detection mechanism. Unfortunately, the security properties of the underlying protocol (Buldas et al. ESORICS 2017) have been specified only in ``game-based'' manner. In other words, there are no guarantees for the protocol being secure in concurrent setting. We remedy this shortcoming by presenting two ideal functionalities $\mathcal{F}^{\textsf{gSpl}}$ and $\mathcal{F}_{\textsf{Sig}}^{\textsf{Spl}}$ for server-supported signing in Universal Composability model. We show that improved RSA server-supported protocol realizes $\mathcal{F}^{\textsf{gSpl}}$ and give practical example of server-supported ECDSA protocol realizing $\mathcal{F}_{\textsf{ECDSA}}^{\textsf{Spl}}$.
Metadata
- Available format(s)
PDF- Category
- Cryptographic protocols
- Publication info
- Preprint.
- History
- 2026-05-05: last updated
- 2024-11-29: published
- Short URL
- https://ia.cr/2024/1941
- License
- https://creativecommons.org/licenses/by-nc-nd/4.0/
BibTeX
@misc{cryptoeprint:2024/1941,
author = {Nikita Snetkov and Jelizaveta Vakarjuk and Peeter Laud},
title = {Universally Composable Server-Supported Signatures for Smartphones},
howpublished = {Cryptology {ePrint} Archive, Paper 2024/1941},
year = {2024},
url = {https://eprint.iacr.org/2024/1941}
}