Bitcoin quantum plan takes shape around P2MR and SHRINCS

Bitcoin’s quantum security roadmap is starting to take shape. In the latest edition of Protocol Watch, researcher Christine D. Kim describes how two proposals, BIP-360 with Pay-to-Merkle-Root and Blockstream Research’s SHRINCS signature scheme, complement each other. Both target the same goal: protecting users before quantum computers become powerful enough to crack existing cryptography. Even so, important steps remain before these solutions are ready for production.

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In brief:

• BIP-360 introduces Pay-to-Merkle-Root to limit the exposure of public keys and to provide an upgrade path for quantum-resistant signatures.
• SHRINCS from Blockstream Research is a signature scheme based on SHA-256 that fits into that upgrade path, but the formal security assessment has not yet been completed.
• Protocol Watch was founded by Christine D. Kim, a former researcher at Galaxy and CoinDesk.

What is BIP-360 and what does Pay-to-Merkle-Root do?

BIP-360 currently holds Draft status and proposes Pay-to-Merkle-Root, abbreviated as P2MR. This mechanism limits the long-term exposure of public keys on the Bitcoin blockchain. That matters because quantum computers could in theory use public keys to calculate the corresponding private keys, which poses a direct threat to funds held for long periods at the same addresses.

P2MR also creates an upgrade path: once sufficiently robust quantum-resistant signatures become available, they can be integrated through this mechanism without having to rewrite the protocol entirely.

SHRINCS completes the upgrade path, but has not yet been fully assessed

Blockstream Research is developing SHRINCS as a complement to this upgrade path. It is a signature scheme based on SHA-256, an algorithm already widely used within Bitcoin and regarded as quantum-resistant. The idea is that users can move their funds to this new scheme before quantum computers actually pose a threat.

But according to Kim, SHRINCS is not yet finished. The formal security assessment is still missing and an independent review has not yet been carried out. That means the scheme cannot yet be designated as safe for use in practice.

Kim published her analysis in edition 54 of Protocol Watch, an independent research publication she founded after her time as a researcher at Galaxy and CoinDesk. The publication focuses on developments in the protocols of Bitcoin and Ethereum. At the time of writing, the Bitcoin price stands at $77K, a decline of 0.1% over the past 24 hours.