Bitcoin’s current transaction signatures rely on elliptic-curve cryptography. A powerful enough quantum computer could, in principle, derive a private key from a public key that has already appeared on the blockchain and then spend the associated coins.
No one can say with certainty when such machines might arrive, but changing Bitcoin’s cryptography would take years of design, review, and network-wide coordination.
That timeline is why researchers have been examining post-quantum alternatives well in advance.
Blockstream Research has put forward SHRINCS, a hash-based signature construction intended to remain secure against quantum attacks while limiting the loss of block space.
Standard post-quantum schemes approved by NIST produce signatures many times larger than Bitcoin’s existing 64-byte Schnorr signatures.
Because each Bitcoin block has a fixed capacity, those larger signatures would sharply reduce how many transactions fit inside one block.
Blockstream estimates that today’s Schnorr signatures support roughly 6.5 transactions per second; a full switch to the NIST hash-based standard SLH-DSA would drop that figure to about 0.36.SHRINCS is designed to recover much of that throughput.
In its compact, stateful mode, signatures begin at 324 bytes and grow by roughly 16 bytes with each additional use of the same public key.
With signatures around 580 bytes, the scheme could support approximately three transactions per second if every spend used the compact path.
SegWit’s existing discount on signature data further softens the impact, so a fivefold increase in raw signature size does not consume five times the block space.
The construction pairs two signing methods under a single public key.
Everyday spending uses a compact stateful path built from an unbalanced XMSS tree of one-time signatures.
If the signer loses that state—for example after restoring a seed on a new device—a larger stateless fallback based on a SPHINCS+ variant remains available.
Security rests on SHA-256, the same hash function Bitcoin already uses for mining and addresses, rather than on a new mathematical assumption.
Jonas Nick and Mikhail Kudinov, who developed the scheme, describe it as the first concrete post-quantum signature proposal built specifically around Bitcoin’s constraints.
They also emphasize that it is not meant to be the network’s last word on the subject and is not optimal on every metric.
The draft lacks a completed security proof, the reference implementation is not production-ready, and certain key-migration mistakes could result in lost funds. Adoption on Bitcoin itself would require a soft fork and broad consensus.
Blockstream has already demonstrated SHRINCS-signed transactions on its Liquid sidechain. Whether the design eventually becomes part of Bitcoin’s consensus rules will depend on further review, formal analysis, and the willingness of the wider community to accept the operational trade-offs of stateful signing.