[BIP proposal] Pay to Schnorr Key Hash (P2SKH)

The recent upgrade to Schnorr signatures for P2WPKH, denoted as Saint Wenhao P2WPKH, marks a significant enhancement in the Bitcoin protocol, aiming to optimize transactional efficiency without altering the fundamental user experience associated with P2WPKH. This modification introduces the adoption of the same Schnorr signature scheme found in Taproot's key-path but applies it to the existing P2WPKH framework, which is characterized by its compact 20-byte hash commitment, absence of script path, and focus on single-key payments. The primary objective of this upgrade is to leverage the witness efficiency benefits provided by Schnorr signatures while maintaining the simplicity and directness favored by users of the P2WPKH model. This approach allows for continued usage of a straightforward payment verification method without necessitating a shift to a 34-byte output type that accommodates a broader range of features unnecessary for certain users.

Despite the enhancements brought about by this upgrade, it is acknowledged that the P2SKH (Schnorr-based Pay to Script Hash) is not equipped with quantum resistance. Like its predecessor P2WPKH, P2SKH relies on the secp256k1 cryptographic algorithm, which is not designed to withstand potential future quantum computing attacks. This limitation underscores a recognized need for eventual migration to post-quantum cryptographic schemes within the Bitcoin network. However, until such technologies are implemented and become standard, P2SKH serves to efficiently meet the needs of current P2WPKH users. The transition to quantum-resistant mechanisms will be necessary in the future, mirroring the expected migration paths for both P2PKH and P2WPKH users to ensure sustained security and functionality of Bitcoin transactions.