Paper 2025/1824
Coppercloud: Blind Server-Supported RSA Signatures
, Cybernetica (Estonia), Tallinn University of Technology, Cybernetica (Estonia), Tallinn University of Technology, Cybernetica (Estonia)Abstract
Privacy-preserving technologies are a well-established area of research for modern digital systems, driven by regulatory mandates, such as the GDPR, and growing demand for the user privacy. A notable example of such technologies is blind signatures: a primitive that supports a creation of privacy-sensitive applications, ranging from secure e-voting and anonymous digital cash to privacy-preserving credentials and identity management systems. In this work, we introduce Coppercloud, a blind server-supported RSA signature scheme designed to enhance privacy in digital identity systems. Coppercloud enables a user to obtain a signature on a message, without revealing its content to the supporting server, while distributing the signing key between the user's device and the supporting server. We formalize the security requirements for blind server-supported signing by defining an ideal functionality ${\mathcal{F}^{\textsf{BlindSpl}}}$, and prove that Coppercloud securely realizes this functionality in the Universal Composability (UC) model.
Note: This is a full version of the paper
Metadata
- Available format(s)
-
PDF
- Category
- Cryptographic protocols
- Publication info
- Published elsewhere. Major revision. SECRYPT 2026
- DOI
- 10.5220/0015000200004103
- Keywords
- Blind SignaturesUniversal ComposabilityRSAServer-Supported Signatures
- Contact author(s)
-
nikita snetkov @ cyber ee
jelizaveta vakarjuk @ cyber ee
alisa pankova @ cyber ee - History
- 2026-07-22: last of 6 revisions
- 2025-10-03: received
- See all versions
- Short URL
- https://ia.cr/2025/1824
- License
-
CC BY-NC-ND
BibTeX
@misc{cryptoeprint:2025/1824,
author = {Nikita Snetkov and Jelizaveta Vakarjuk and Alisa Pankova},
title = {Coppercloud: Blind Server-Supported {RSA} Signatures},
howpublished = {Cryptology {ePrint} Archive, Paper 2025/1824},
year = {2025},
doi = {10.5220/0015000200004103},
url = {https://eprint.iacr.org/2025/1824}
}
