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Bitcoin researchers propose quantum fix that would not crowd out transactions
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- DeepHorus
Bitcoin researchers at Blockstream have introduced a novel quantum-resistant signature scheme called SHRINCS, designed to secure Bitcoin transactions against future quantum computing threats without severely limiting network capacity. The proposal, published on Thursday, addresses a critical vulnerability: a sufficiently powerful quantum computer could theoretically break Bitcoin's current elliptic-curve cryptography, allowing an attacker to forge signatures and steal coins from addresses where public keys are exposed, including over 1.1 million BTC belonging to Satoshi Nakamoto.
The challenge with existing post-quantum signatures standardized by NIST is their large size. If Bitcoin were to adopt a standard like SLH-DSA, transaction throughput could plummet from roughly 6.5 transactions per second (TPS) with current Schnorr signatures to just 0.36 TPS, as larger signatures fill up the limited space in blocks far more quickly. This would drastically reduce the network's utility and scalability.
SHRINCS aims to solve this efficiency problem. Its signatures start at approximately 324 bytes, compared to 64 bytes for Schnorr, and grow by about 16 bytes per key use. In a configuration targeting three TPS, it uses 580-byte signatures. This moderate size increase is partially mitigated by Bitcoin's SegWit upgrade, which gives a discount to signature data, meaning a five-fold increase in size does not consume five times the block space.
A key feature of SHRINCS is its foundation on SHA-256, the same hash function already integral to Bitcoin's security and mining. This means it does not rely on new, untested mathematical assumptions, potentially simplifying its integration. Researchers Jonas Nick and Mikhail Kudinov describe it as the first concrete post-quantum signature proposal specifically tailored for Bitcoin's unique constraints.
However, the proposal is still in an early draft stage. It lacks a completed security proof, and the accompanying reference software is not intended for production use. The researchers also warn of risks, noting that moving certain keys between incompatible wallets could lead to a loss of funds. Deploying SHRINCS on Bitcoin would ultimately require a soft fork upgrade and widespread network consensus.
This development represents a significant step in the proactive defense of Bitcoin's long-term security. While not a final or perfect solution on every measure, SHRINCS offers a tangible pathway to mitigate the quantum threat while preserving much of Bitcoin's transactional capacity. The proposal will now undergo scrutiny from the broader cryptographic and Bitcoin developer communities as the timeline for quantum computing threats continues to be debated.
