Bitcoin’s Quantum-Resistance Strategy: Introducing BIP-360 and Pay-to-Merkle-Root
The realm of cryptocurrency is ever-evolving, and Bitcoin’s latest move towards fortifying its security against quantum threats has taken a significant leap. An updated draft of Bitcoin Improvement Proposal (BIP) 360 has been integrated into the official Bitcoin Improvement Proposals repository. This new proposal suggests an innovative output type adjacent to Taproot, aiming to reduce vulnerability to potential quantum key-recovery attacks in the future.
Bitcoin Developers’ Pioneering Step Towards Quantum Security
Anduro, a research platform supported by Marathon Digital, highlighted on social media that the latest update introduces Pay-to-Merkle-Root (P2MR). This proposed output type eliminates Taproot’s quantum-susceptible key-path spend while maintaining full compatibility with Tapscript and script trees.
Advertisement Banner
BIP-360 is characterized as a “Consensus (soft fork)” proposal. It defines P2MR as a new SegWit v2 output, which commits directly to the Merkle root of a script tree instead of a modified public key, as seen in Pay-to-Taproot (P2TR). The significance is clear: P2MR outputs can only be spent through script-path logic, completely removing the key-path spend.
The Objective and Implications of BIP-360
BIP-360 aims to create minimal disruptions while delivering additional protection for users. The document states, “This proposal suggests a new output type: Pay-to-Merkle-Root (P2MR), via a soft fork. P2MR functions similarly to P2TR outputs but without the key path spend.” It further notes that the protection targets “long exposure attacks by Cryptographically Relevant Quantum Computers (CRQCs)” and potential future cryptanalytic methods that may compromise Bitcoin’s elliptic curve cryptography (ECC).
Long vs. Short Exposure Attacks
A crucial aspect of BIP-360 is its precise terminology, distinguishing between “long exposure” attacks, where public keys are publicly accessible for extended durations, and “short exposure” attacks, which target public keys briefly exposed in the mempool during an unconfirmed spend.
Limitations and Future Steps
BIP-360 acknowledges that P2MR does not offer complete protection against quantum threats. “It is noteworthy that proposed P2MR outputs are only resistant to ‘long exposure attacks’ on elliptic curve cryptography,” the document clarifies. “Protection against more sophisticated quantum attacks, including those targeting private key recovery from public keys in the mempool during transaction confirmation (a.k.a. ‘short exposure attacks’), may necessitate the introduction of post-quantum signatures in Bitcoin.” The authors have expressed their intention to introduce separate proposals addressing these concerns as research progresses.
Compatibility and the Path Forward
The proposal emphasizes tapscript compatibility, positioning P2MR as a script-tree output type. If Bitcoin incorporates post-quantum signature opcodes, P2MR could facilitate a smoother transition than older script mechanisms that lack tapscript’s evolutionary path.
Anduro emphasized that the change is implemented as a soft fork, ensuring it does not disrupt existing Taproot outputs. Instead, P2MR would represent a new output type, featuring bech32m addresses starting with bc1z, distinct from the current bc1p Taproot UTXOs.
Potential Trade-offs and Privacy Considerations
While P2MR removes key-path spends, it sacrifices Taproot’s most compact witness path—a single Schnorr signature. The BIP estimates that a minimal P2MR spend witness is 37 bytes larger than a Taproot key-path spend, although it remains smaller than an equivalent Taproot script-path spend due to P2MR’s omission of an internal public key.
Privacy dynamics shift as well. With every spend revealing a script tree, P2MR users inherently signal that they are spending from a script tree—something Taproot key-path spends can avoid.
Addressing Concerns and Looking Ahead
Anduro underscored that the update addresses concerns that Bitcoin developers were not adequately addressing quantum threats. The addition of Isabel Foxen Duke as a co-author aims to enhance the BIP’s clarity for the general public, not just the Bitcoin developer community.
Though BIP-360 remains in “Draft” status, its integration into the official repository marks a significant milestone. The proposal shifts the quantum-safety discussion from theoretical concerns to a concrete consensus change proposal, inviting wallets, libraries, and reviewers to analyze it line-by-line.
The next phase of the debate will likely focus on whether “prepared not scared” opt-ins like P2MR provide sufficient groundwork or if Bitcoin will eventually need to tackle post-quantum signatures and the operational realities of large-scale value migration.
Commitment to Editorial Integrity
Our Editorial Process at Bitcoinist prioritizes delivering meticulously researched, accurate, and unbiased content. We adhere to stringent sourcing standards, ensuring every page undergoes rigorous review by our team of top technology experts and seasoned editors. This commitment guarantees the integrity, relevance, and value of our content for our readers.
