Proposing a P2QRH BIP towards a quantum resistant soft fork

The discussion revolves around the proactive measures against potential quantum computing threats to Bitcoin's security, emphasizing the importance of developing a quantum-resistant address type without resorting to immediate hard or soft forks. The suggested approach includes finalizing a secure and straightforward quantum-proof signature scheme, such as Lamport signatures, despite their large size, and integrating these into SegWit version 2 addresses (bc1z…). This integration would combine ECDSA, Schnorr, and Lamport signatures, enabling immediate implementation by wallets through standard practice of including at least one Quantum Lamport signature path within every taproot address's script tree. This strategy offers a safeguard against sudden quantum attacks by facilitating a swift transition to the new quantum address type via a soft fork, thereby protecting transactions from being compromised.

The plan acknowledges the current improbability of a quantum computer breaching Bitcoin encryption within the next 15-20 years but argues for preemptive action to leverage time for developing robust mathematical solutions suitable for Bitcoin. It proposes a gradual consensus shift towards lattice-based cryptography and eventually to compact, proven supersingular EC Isogeny cryptography, all achievable without any blockchain forks. In a future quantum attack scenario, the majority of users could switch their taproot addresses to the latest quantum algorithm, with fallback options for others based on older algorithms or direct mining pool connections for spend transactions, albeit with some trust assumptions in miners.

Furthermore, the strategy highlights the tactical advantage of taproot addresses in deterring quantum attacks. By making the primary path unspendable and potentially creating honeypot addresses, it sets traps for quantum computers that, if sprung, would alert the Bitcoin community to the presence of such a threat. This approach relies on game theory, suggesting that an adversary with quantum capabilities would likely refrain from attacking Bitcoin to avoid revealing their advantage. Additionally, it mentions recommendations for exchanges and large ETFs to use taproot addresses with unspendable primary paths for significant holdings, enhancing collective security.

The narrative concludes by emphasizing the value of time this method buys for the development of quantum-resistant technologies and maintaining vigilance against quantum threats. It suggests the eventual goal is achieving a compact quantum proof of knowledge, complemented by client-side verification and quantum trustless bridges, ideally before a real quantum threat emerges. The interim solution involves leaving behind a series of impractically large quantum spending paths in never-revealed script leaves, serving as a temporary measure until more feasible quantum-resistant solutions are developed.