Perhaps the simplest possible quantum-security upgrade

This approach is designed to provide security through economic assumptions already integral to transaction finality, without necessitating a complete overhaul of the existing Script design. The core of this method involves a minimal new introspection primitive, leveraging a single opcode that reveals a chain-derived challenge associated with the spent output's creation block hash. The challenge's offset, determined by the locking script, allows for variable confirmation depths tied to the value at risk, thus offering higher resistance to manipulation through deeper confirmation waits.

This mechanism employs a commit-challenge-response authentication model, where the future state of the blockchain itself supplies the challenge. Authorization demands both a traditional signature verification and a novel, delayed, chain-conditioned hash-based proof. This dual requirement ensures that the system's security remains robust against quantum threats while maintaining compatibility and reliance on current security assumptions. The implementation does not increase transaction sizes or introduce complex cryptographic needs, focusing instead on an economically secure model using pre-committed randomness revealed in conjunction with a blockchain challenge hash.

Erik has developed Python code to illustrate this concept in practice. The code demonstrates how a spender can publish an ephemeral anchor transaction, committing to a future secret without immediate disclosure. This commitment is later paired with the secret's revelation and the transaction spend in subsequent blocks. A new opcode verifies the temporal gap between the anchor transaction and its corresponding spend, creating an information asymmetry that secures against quantum computational advances. This solution emphasizes time-based asymmetry over conventional signatures, providing a practical and incremental path towards quantum-resistant Bitcoin transactions without altering fundamental transaction or address structures. Erik invites further discussion and development towards a Bitcoin Improvement Proposal (BIP) for this security construct, signaling open collaboration for enhancing Bitcoin's quantum resilience.