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

The latest amendments focus on transitioning P2QRH to a script-only version of Taproot, eliminating the quantum-vulnerable key-spend pathway. This move prioritizes direct commitment to the tapleaf merkle root, computed by taproot, thereby fortifying the protocol against quantum-induced vulnerabilities. The technical adjustments include defining the scriptPubKey for P2QRH outputs as OP_PUSHNUM_3 OP_PUSHBYTES_32, leveraging the familiarity and infrastructure of P2TR to ensure seamless adaptation within the Bitcoin community. By omitting the taptweak steps and emphasizing script and tapleaf compatibility, this approach simplifies implementation while significantly bolstering defenses against long-exposure attacks—deemed more likely to precede short-exposure ones due to technological progression.

Furthermore, the updated proposal presents a strategic foresight regarding Post-Quantum (PQ) signatures, proposing their discussion and specification be conducted independently of BIP-360. This separation allows for continuous enhancement of P2QRH without binding it to any specific PQ signature algorithms prematurely. It is suggested that tapscript PQ signature verification opcodes for ML-DSA (CRYSTALS-Dilithium) and SLH-DSA (SPHINCS+) could be introduced through OP_SUCCESSx opcodes, providing a flexible mechanism for future activation of PQ signatures. This method not only facilitates the potential introduction of new signature algorithms but also ensures the Bitcoin protocol can adapt to emerging cryptographic standards without necessitating comprehensive overhauls.

These developments underscore a proactive approach to cryptographic evolution, recognizing the necessity for Bitcoin to remain secure in an era marked by rapid advances in quantum computing. By decoupling the introduction of PQ signatures from the core enhancements proposed in BIP-360, the Bitcoin community is afforded the flexibility to address quantum threats in a phased and informed manner. This strategy reflects a broader vision for Bitcoin's sustainability, focusing on incremental, forward-compatible improvements that safeguard the protocol against both current and speculative future vulnerabilities.