Post-Quantum Cryptography
TECHNOLOGYDEFINITION
Cryptographic methods designed to stay secure even against attacks from a sufficiently powerful quantum computer. Bitcoin currently relies on elliptic-curve cryptography, which a quantum computer could theoretically break; post-quantum schemes are built on different math believed to resist that kind of attack.
The most-studied family of post-quantum candidates for bitcoin is hash-based signatures, which derive their security from cryptographic hash functions like SHA-256 rather than from elliptic curves. Because no quantum algorithm is known to meaningfully speed up attacks on well-designed hash functions, these schemes are considered a safer long-term bet — the tradeoff is that hash-based signatures are typically much larger than today's signatures, sometimes by 100x or more.
No quantum computer today comes close to threatening bitcoin's cryptography, and estimates for when one might vary widely. The reason researchers work on post-quantum designs now anyway is timing: adopting new cryptography across a decentralized network with millions of users requires a coordinated soft fork, wallet upgrades, and years of lead time — work that has to start well before the threat becomes real, not after.
IN A SENTENCE
"Blockstream's SHRINCS proposal is a post-quantum cryptography candidate for bitcoin — a backup signature scheme that would still work even if a quantum computer could break today's math."
Key facts
Common questions
Is bitcoin vulnerable to quantum computers right now?
No known quantum computer today is capable of breaking bitcoin's cryptography. The concern is forward-looking: because a network-wide cryptography upgrade takes years to design, test, and roll out, researchers are preparing candidates well before any real threat materializes.
Why not just switch to post-quantum signatures today?
Current post-quantum signature candidates are dramatically larger than bitcoin's existing signatures, which would raise transaction fees and slow down verification across every node on the network. Researchers are working to shrink that cost before any such upgrade would be proposed.