OP_CIV - Post-Quantum Signature Aggregation

The discussion centers on a novel idea related to Bitcoin transactions, specifically addressing the limitations that could arise when committing each script pubkey to previous outputs in a transaction. This approach poses practical challenges, particularly for deterministic backup wallets which represent a significant portion of modern Bitcoin usage. The implementation of this concept could be especially difficult for offline or hardware wallets due to the complexity and resource requirements involved.

A more conservative use case is highlighted, focusing on the aggregation of inputs controlled by the same owner. In such scenarios, the essential requirement isn't to prove the commitment of one UTXO to another but rather to demonstrate that two or more UTXOs are spendable under the same pubkey and that their common owner has authorized their spending with a single signature. This shifts the focus from committing a taptree to pre-existing UTXOs, which introduces statefulness, to committing a taptree to a deterministic set of pubkeys. An example provided suggests using "the nearest 100 addresses in the same BIP32 account" for this purpose. At the time of spending, revealing the same pubkey's script leaf across all inputs, alongside a signature covering all these inputs, would facilitate stateless address generation and enable a single signature to authenticate all common inputs within a wallet.

This approach, however, comes with privacy trade-offs. Specifically, it would strengthen the common-owner heuristic, making the association between commonly owned inputs provable on-chain, thereby potentially undermining UTXO privacy. The discussion acknowledges that operating code (OP_CIV) might have a similar impact on chain analysis techniques. Despite these concerns, the potential for fee savings, especially for large entities like exchanges that consolidate numerous UTXOs, is considered possibly advantageous. The conversation reflects a balanced view on evolving Bitcoin transaction methodologies, recognizing both the technical hurdles and the strategic benefits that could accompany their adoption.