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

The discourse revolves around the P2QRH protocol, emphasizing its dual capability to enable quantum-secure transactions alongside the utilization of Schnorr signatures to mitigate high transaction fees. This approach allows users and exchanges to adopt P2QRH without incurring significant costs while benefiting from enhanced security against quantum computing threats. However, the critique raises concerns about the effectiveness of this security measure in scenarios where a Cryptographically Relevant Quantum Computer (CRQC) emerges. The argument posits that if elliptic curve (EC) cryptography is not disabled in the wake of a CRQC's existence, Bitcoin could potentially lose all value, as the primary function of securing millions of BTC would be compromised.

Further analysis dismisses the scenario of maintaining EC cryptography in a quantum-threatened landscape, suggesting that any discussion should proceed under the assumption that EC would inevitably be disabled in such cases. This presumption shifts the focus towards the practicality and relevance of P2QRH and PQC (Post-Quantum Cryptography) mechanisms. The critique argues that for mixed EC-or-PQC spending conditions, the P2TR protocol offers superior functionality, privacy, and cost-effectiveness compared to P2QRH. However, the potential utility of P2QRH in purely PQC conditions remains uncertain without a definitive PQC scheme in place.

Moreover, the commentary touches upon the notion that P2QRH could have been envisioned as a protocol that inherently disables EC cryptography, thereby transitioning exclusively to quantum-resistant outputs. Such an approach would align with policies or consensus rules mandating the use of PQC outputs, though it is noted that revealing minimal information through outputs is preferable. Despite initial assumptions, it becomes apparent that BIP360 does not aim to fulfill this concept, leading to skepticism regarding the overall purpose and efficacy of the P2QRH proposal.