Bitcoin’s Post-Quantum Roadmap Takes Shape Around P2MR And SHRINCS, But Key Gaps Remain
Bitcoin’s response to the threat posed by quantum computers is gradually converging into a coherent strategy, according to Protocol Watch founder Christine D. Kim, who outlined how several independent proposals could combine into a layered defense for the network.
Two complementary proposals form the core of what can be done before cryptographically relevant quantum computers (CRQCs) become a reality. BIP-360, still in draft status, introduces Pay-to-Merkle-Root (P2MR), a new output type that would be activated via a soft fork. Its primary function is to conceal users’ public keys until funds are spent — a critical safeguard, since a sufficiently powerful quantum computer could otherwise derive a private key from an exposed public key. P2MR also supports multiple spending paths and is designed to be cryptography-agnostic, meaning it could accommodate future post-quantum signature schemes without further structural changes.
The second pillar is SHRINCS (“Shrunken SPHINCS”), a hash-based signature scheme developed by Blockstream Research. Notably, it relies exclusively on SHA-256 — the same hash function Bitcoin already uses for mining — avoiding any new mathematical assumptions. According to its draft BIP, authored by Bitcoin Core contributor “conduition,” SHRINCS public keys are just 48 bytes, with stateful signatures as small as 548 bytes, making it roughly an order of magnitude more compact than comparable post-quantum schemes. Paired with P2MR and a dedicated verification opcode, SHRINCS would give users an optional, backward-compatible path to quantum-resistant security well before CRQCs exist.
Rescue Protocols for Late Migrants
For users who fail to migrate in time, developers have proposed two “rescue” mechanisms: Lifeboat, presented by researcher Tadge Dryja, and Dropkick, authored by conduition. Both rely on commit-reveal schemes, allowing users to prove on-chain that they controlled an address before any attacker did, thereby enabling safe migration of coins even after quantum adversaries emerge. Lifeboat would activate automatically via a conditional soft fork triggered by evidence of a quantum attack on-chain.
However, developers caution that significant questions remain unresolved. SHRINCS lacks a formal security proof and independent peer review; its BIP, published in late August, explicitly acknowledges this gap. Signature size is another concern — SHRINCS signatures are still roughly ten times larger than Bitcoin’s current Schnorr signatures, raising questions about block space if widely adopted, with aggregation research still ongoing. Finally, the fate of lost coins, whose owners cannot migrate them, remains an open and contentious question. As Kim notes, the pieces are coming together — but Bitcoin’s quantum problem is far from solved.
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About The Author
Alisa, a dedicated journalist at the MPost, specializes in crypto, AI, investments, and the expansive realm of Web3. With a keen eye for emerging trends and technologies, she delivers comprehensive coverage to inform and engage readers in the ever-evolving landscape of digital finance.
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Alisa, a dedicated journalist at the MPost, specializes in crypto, AI, investments, and the expansive realm of Web3. With a keen eye for emerging trends and technologies, she delivers comprehensive coverage to inform and engage readers in the ever-evolving landscape of digital finance.
