Add BIP: QES2 – Hybrid PQC-based Digital Signature Algorithm

Summary: This pull request introduces a new Bitcoin Improvement Proposal (BIP) for QES2, a hybrid digital signature algorithm that combines post-quantum cryptography (PQC) with traditional ECDSA. The proposal aims to address the potential vulnerabilities posed by quantum computing while preserving backward compatibility with existing Bitcoin infrastructure.

Details:

Abstract: QES2 leverages a dual-signature mechanism to incorporate both a post-quantum signature and a classical ECDSA signature into Bitcoin transactions.

Motivation: With the emerging threat of quantum computers, classical cryptographic methods may become vulnerable. QES2 presents a transitional solution that enhances security during the shift towards quantum-safe systems.

Specification: The BIP outlines the structure, key generation, signing, and verification methods for the hybrid scheme.

Rationale: The hybrid approach ensures that if one signature method is compromised, the other still provides protection, offering a balanced trade-off between security and backward compatibility.

Reference Implementation: A reference implementation will be linked later for further review and testing.