OP_CAT Enables Winternitz Signatures

The conversation revolves around the necessity for smaller signature schemes within a post-quantum Bitcoin network, highlighting the potential of lattice-based cryptography over larger hash-based alternatives like Lamport, WOTS, or SPHINCS signatures. These larger signatures pose challenges, such as reducing transactions per second (TPS) or necessitating increased block sizes—outcomes that the community aims to avoid.

One practitioner suggests an interim solution involving WOTS, acknowledging its limitations but valuing its minimal assumptions compared to more novel approaches like lattices. The ideal future posited involves developing a compact, quantum-resistant signature scheme facilitating easy migration via new opcodes or address formats. This approach underscores a strategic diversification in cryptographic methods to safeguard against consensus failures or unforeseen vulnerabilities in adopted schemes.

Further technical discourse introduces concrete implementations that leverage Bitcoin's scripting capabilities to enable post-quantum signature algorithms. Jeremy Rubin's work with OP_CAT and Lamport signatures is cited as foundational, achieving significantly reduced witness sizes by employing RMD-160 hashes. Building on this, another contribution showcases the application of Winternitz One-Time Signatures (WOTS) within Bitcoin's scripting environment. This method utilizes SHA256 hash chains and a checksum compression technique inspired by the SPHINCS+ paper, demonstrating a prototype that considerably lowers script and witness stack sizes compared to previous Lamport signature implementations.

This discussion not only highlights the ongoing efforts to quantum-proof Bitcoin but also points to essential technical innovations and community collaboration aimed at securing the network's future. The sharing of ideas and prototypes, including links to GitHub for code review and testing (prototype implementation), exemplifies the open-source ethos and collective problem-solving characteristic of Bitcoin development.