Blockstream Publishes SHRINCS Post-Quantum Signature Scheme as Bitcoin Improvement Proposal

Blockstream's SHRINCS post-quantum signature scheme has been published as a Bitcoin Improvement Proposal (BIP), aiming to secure Bitcoin against quantum computer attacks. The proposal, which is still at an early stage, uses hash-based signatures that are smaller than other post-quantum schemes but would still require the blockchain to be around nine times larger than it is today.

According to Blockstream Research's Jonas Nick, SHRINCS is not intended to be Bitcoin's 'final' signature scheme and has its own set of limitations. The scheme uses one-time keys that are stored on a device, making it stateful, but this also means that signatures get larger by 16 bytes each time they are used.

The BIP warns that the security proof for SHRINCS is still TODO, meaning it's not yet fully validated. Yoon Auh, founder of BOLTS Technologies, expressed concerns about the added complexity and fragility introduced by SHRINCS' designers to maximize throughput and minimize computation cycles. Blockstream has been researching and optimizing the scheme throughout 2026.