Bitcoin Prepares for Quantum Computing Threat With New SHRINCS Signature Proposal

The Quantum Computing Challenge Facing Bitcoin

Bitcoin faces a looming cryptographic vulnerability that could potentially compromise the security of billions in digital assets. Scientists broadly agree that sufficiently advanced quantum computers possess the theoretical capability to reverse-engineer private keys from public keys, a feat that would enable attackers to steal funds from virtually any Bitcoin address.

While debate persists about the timeline for quantum computer maturation, major research institutions are taking proactive steps. Blockstream, the prominent Bitcoin infrastructure company, has positioned itself at the forefront of developing defensive solutions. The firm published a Bitcoin Improvement Proposal for SHRINCS, a new post-quantum signature scheme specifically engineered for Bitcoin’s constraints and requirements. Earlier this year, the scheme was successfully tested in production on Blockstream’s Liquid sidechain.

SHRINCS: Solving the Size-Performance Dilemma

The primary challenge in upgrading Bitcoin to quantum-resistant cryptography is managing a fundamental tradeoff: security versus scalability. Post-quantum signature schemes endorsed by the National Institute of Standards and Technology are dramatically larger than Bitcoin’s existing cryptographic signatures, ranging from 38 to 123 times bigger. Deploying these standard algorithms would severely cripple Bitcoin’s transaction throughput, potentially reducing it to less than 1 transaction per second.

Blockstream’s researchers developed SHRINCS by compressing hash-based post-quantum signatures to approximately 13.23 times smaller than NIST-approved alternatives. The resulting signatures range from a minimum of 548 bytes to a maximum of 4,619 bytes, paired with a 48-byte public key. This optimization preserves network functionality: under SHRINCS, Bitcoin could maintain approximately 3 transactions per second—roughly consistent with today’s throughput levels. By contrast, deploying the NIST lattice-based scheme ML-DSA would reduce the network to 0.5 TPS, while the NIST hash-based SPHINCS+ would bottleneck the system to just 0.36 TPS.

Bitcoin’s Segregated Witness architecture amplifies these efficiency gains. Witness data, which includes signatures, occupies only one-quarter the blockspace of standard transaction data, meaning SHRINCS signatures—while nine times larger than current Schnorr signatures—consume proportionally less resources than raw size comparisons suggest.

Promising But Not Yet Mature

Jonas Nick of Blockstream Research called SHRINCS “the first concrete proposal for a post-quantum signature scheme designed specifically for Bitcoin,” though cautioning it represents a practical tradeoff rather than an optimal final solution. The scheme benefits from Bitcoin-native design, full BIP-39 seed recovery support, and reliance on the same SHA-256 assumptions underlying Bitcoin mining itself.

However, the proposal remains early-stage. The security proof is incomplete, independent cryptographic audits are pending, and the scheme lacks the years of public analysis that established NIST alternatives have undergone. Each SHRINCS signature requires a new one-time key, adding operational complexity. Network implementation would require storing used keys on individual devices rather than relying on simpler stateless structures.

Despite these caveats, the March 2026 production deployment on Blockstream’s Liquid sidechain—which even embedded the Bitcoin whitepaper in the test—demonstrated practical viability. A quantum-resistant Bitcoin strengthens the security foundation of the entire cryptocurrency ecosystem, protecting distributed finance against future cryptographic threats.

Source: Blockstream, via Cointelegraph. Not financial advice.