SHRINCS Bitcoin Improvement Proposal Published, But Quantum-Secure Upgrade Comes With Trade-Offs
A new Bitcoin Improvement Proposal for Blockstream's experimental post-quantum signature scheme, SHRINCS, has been published, offering a potential path to quantum security while introducing stateful complexity and other trade-offs.
p>Blockstream Research has published a Bitcoin Improvement Proposal (BIP) for SHRINCS, an experimental post-quantum signature scheme designed specifically for Bitcoin. While scientists agree that sufficiently advanced quantum computers could eventually threaten Bitcoin by reversing private keys from public keys, standard post-quantum signature schemes endorsed by the National Institute of Standards and Technology (NIST) are significantly larger than existing Bitcoin signatures and could severely slow down the blockchain.
p>Blockstream researchers Jonas Nick and Mikhail Kudinov unveiled SHRINCS, a hash-based post-quantum signature scheme, in December 2025, with the opcode proposal published in May. Although SHRINCS is roughly nine times larger than Bitcoin’s existing Schnorr signatures, its size is mitigated by Segregated Witness, allowing the network to maintain transaction throughput similar to current levels.
The Catch: Statefulness and Complexity
p>Despite its advantages in preserving block economics, SHRINCS comes with notable drawbacks. As warned in the BIP, a security proof is still pending, meaning the research is not yet a cryptographically mature proposal that has been fully validated. Furthermore, unlike stateless schemes, SHRINCS is stateful and stores used keys directly on the user's device to save space.
This design choice creates additional user failure modes and maintenance obligations. Signatures grow by 16 bytes each time they are used, and losing a device requires a large stateless fallback transaction of around 5,777 bytes to recover funds. Industry experts note that while the scheme represents pragmatic engineering to maximize throughput and minimize computation, it introduces added complexity and potential fragility.
Ongoing Development and Governance Challenges
p>Blockstream has continued refining the scheme, recently demonstrating that SHRINCS can run on common hardware wallets, though the BIP cautions that importing keys across incompatible implementations could result in lost funds. The companion scheme previously known as SHRIMPS has also been incorporated as a built-in stateless path under the same 48-byte public key, optimized to be about 26% smaller.
p>While Blockstream has separated the SHRINCS proposal from more radical changes like zero-knowledge proof aggregation or block size increases to ease adoption, experts emphasize that the primary hurdle for any quantum upgrade remains governance rather than cryptography.
