ALT-34 · Paper · 23 Oct 2026
The SIKE break: a post-quantum finalist falls to a laptop
In 2022 a candidate in NIST's post-quantum competition was broken in about an hour on one ordinary processor core, using mathematics from 1997. Why that is the system working, not failing.
- 2011Isogeny-based key exchange (SIDH) is proposed.
- Jul 2022SIKE advances to NIST's fourth round as an alternate candidate.
- 30 Jul 2022Castryck and Decru publish “An efficient key recovery attack on SIDH”.
- To break SIKEp434 on a single core
- ~62 minCastryck & Decru, IACR ePrint 2022/975
Why it is good news
Open competitions exist so that schemes are attacked before they are deployed. SIKE fell in public, in time, and the standards that followed kept a hash-based backup precisely because new mathematics can appear suddenly.
Our reading
Analysis — Altumptic's interpretation of the sources below.
- Young cryptographic assumptions deserve hybrid deployment, never solo deployment.
- Security levels are estimates of what we know how to attack, not guarantees.
- Open review beats secret design, even when — especially when — it breaks things.
What it means for you
- Deploy post-quantum cryptography in hybrid mode with a classical algorithm.
- Use standardised algorithms (ML-KEM, ML-DSA), not candidates.
- Keep algorithms swappable so a break is a configuration change.
Sources
- Castryck & Decru — An efficient key recovery attack on SIDH (IACR ePrint 2022/975)
- NIST — Status report on the fourth round
Altumptic was not involved in this research. Figures are as published by the sources above.
Cite this entry
Altumptic Lab (2026). ALT-34 — The SIKE break: a post-quantum finalist falls to a laptop. 23 Oct 2026. altumptic.com/research/sike-break-2022