Changes to BIP-360 - Pay to Quantum Resistant Hash (P2QRH)

The discussion revolves around the effectiveness of a current proposal in enhancing quantum protection within Bitcoin's protocol. The initial critique suggests that the proposal fails to achieve meaningful quantum protection unless it specifically disables Deterministic List (DL) spending through a separate consensus change. This critique is countered with the argument that Pay-to-Taproot (P2TR) transactions are indeed susceptible to a long exposure attack through key path spending, a vulnerability that does not apply to the proposed P2QRH. By incorporating P2QRH, TapScript becomes safeguarded against such attacks, thereby making Taproot transactions secure in a post-quantum scenario. This modification allows wallet users the flexibility to choose between spending their coins using either Elliptic Curve Cryptography (ECC) or Post-Quantum Cryptography (PQC), depending on their preference for script path.

The significance of P2QRH lies in its ability to make Taproot applicable and useful in a context where quantum threats are a consideration. Without such a provision, Taproot would remain ineffective against potential quantum computing advances. Furthermore, the assertion highlights an important consideration regarding the potential risks associated with disabling key path spends in P2TR transactions. Such a move could inadvertently lead to the confiscation of funds, a scenario the author strongly advises against, especially given the nascent adoption of P2TR compared to the more widespread use of P2PKs and reused addresses. The comparison of coins held in P2TR versus those in P2PKs or reused addresses—150K versus 1.7M—underscores the relatively limited impact of P2TR in the current state but also emphasizes the importance of ensuring its security against future quantum threats.