Paper 2025/705 Original: eprint.iacr.org/2025/705 ↗
Breaking ECDSA with Two Affinely Related Nonces
Abstract
The security of the Elliptic Curve Digital Signature Algorithm (ECDSA) depends on the uniqueness and secrecy of the nonce, which is used in each signature. While it is well understood that nonce $k$ reuse across two distinct messages can leak the private key, we show that even if a distinct value is used for $k_2$, where an affine relationship exists in the form of: \(k_m = a \cdot k_n + b\), we can also recover the private key. Our method requires only two signatures (even over the same message) and relies purely on algebra, with no need for lattice reduction or brute-force search(if the relationship, or offset, is known). To our knowledge, this is the first closed-form derivation of the ECDSA private key from only two signatures over the same message, under a known affine relationship between nonces.
Metadata
- Available format(s)
PDF- Category
- Attacks and cryptanalysis
- Publication info
- Preprint.
- History
- 2025-04-18: last updated
- 2025-04-18: published
- Short URL
- https://ia.cr/2025/705
- License
- https://creativecommons.org/licenses/by/4.0/
BibTeX
@misc{cryptoeprint:2025/705,
author = {Jamie Gilchrist and William J Buchanan and Keir Finlow-Bates},
title = {Breaking ECDSA with Two Affinely Related Nonces},
howpublished = {Cryptology {ePrint} Archive, Paper 2025/705},
year = {2025},
url = {https://eprint.iacr.org/2025/705}
}