Bitcoin Developers Propose BIP 360 to Mitigate Long-Exposure Quantum Vulnerabilities

Bitcoin developers Hunter Beast, Ethan Heilman, and Isabel Foxen Duke have introduced BIP 360, proposing a new consensus soft fork named Pay-to-Merkle-Root (P2MR) ¹. Assigned on Dec. 18, 2024, the draft specification aims to protect Bitcoin script trees against long-exposure quantum computer attacks by removing the direct key path spend found in Pay-to-Taproot (P2TR) outputs ¹.

Under current network rules, P2TR outputs expose internal public keys directly on the ledger, leaving them vulnerable to Shor's algorithm, which enables cryptographically relevant quantum computers to resolve the Discrete Logarithm Problem and derive private keys ¹. P2MR circumvents this vulnerability by committing exclusively to the 32-byte Merkle root of a script tree hashed with the "TapBranch" tag, rather than tweaking an internal key ¹. This architecture provides tapscript support while concealing public keys until a spending transaction is published ¹.

Long vs. Short Exposure Quantum Risks

The authors note that P2MR addresses "long exposure attacks," which target public keys exposed indefinitely across blockchain history, such as reused addresses, legacy Pay-to-Public-Key (P2PK) outputs, and standard Taproot addresses ¹. However, P2MR does not protect against "short exposure attacks"—scenarios where quantum attackers recover private keys from public keys exposed in the mempool before a transaction confirms ¹. Mitigating short-exposure risks will ultimately require integrating native post-quantum signature schemes into the protocol ¹.

The initiative comes as broader digital asset ecosystems consider quantum readiness, including ongoing research into post-quantum migration frameworks ¹. The BIP 360 proposal references federal transitions like the CNSA 2.0 timeline mandating software upgrades to post-quantum algorithms by 2030, alongside NIST IR 8547 guidelines aiming to phase out standard elliptic curve cryptography in US federal systems after 2035 ¹. The authors plan to submit a separate proposal addressing post-quantum signatures following further research ¹. At the time of writing, $BTC traded at $83,308.