[0/4] A Bitcoin Scripting Proposal BIP Quartet

The email from Rusty Russell introduces a discussion on the intricacies of naming and functionality within Tapscript v2, focusing on the clarification and enhancement of script selection mechanisms for Bitcoin development. The message emphasizes the confusion arising from the multiple uses of the term "script" within the context of Bitcoin transactions, suggesting a more precise naming convention to avoid ambiguity. Specifically, it proposes renaming certain selectors to reflect their function more accurately, such as using TXSELECT_INPUT_OUTPOINT_{AMOUNT,SCRIPTPUBKEY} (or alternatives like COIN or UTXO) to denote that these are derived from the outpoint being spent, rather than directly from the input.

Further, Russell suggests adding a new selector, TXSELECT_INPUT_OUTPOINT_HEIGHT, which would push the height of the block in which the coin being spent was confirmed onto the stack. This addition aims to convert relative timelocks into absolute ones, facilitating the implementation of eltoo mechanisms for state finalisation in blockchain protocols. The proposal outlines how this feature could mitigate delays in adversarial scenarios by allowing for an on-chain transaction that replaces a relative timelock with an absolute one, ensuring timely state finalisation regardless of subsequent updates by counterparties.

Additionally, the email touches upon the potential inclusion of TXSELECT_INPUT_OUTPOINT_WAS_COINBASE, which might serve utility in redesigning drivechains to reduce the need for additional consensus support by leveraging miner influence over coin movements. This suggestion underscores an ongoing exploration of ways to refine and evolve Bitcoin scripting capabilities to support more sophisticated and secure transaction mechanisms.

The conversation is enriched with a reference to a detailed discussion on contract-level relative timelocks, ancestry proofs, and singletons, available at delvingbitcoin.org. This link provides readers with a deeper dive into the technical considerations and potential implementations of the concepts discussed in Russell's email, highlighting the collaborative and open-ended nature of Bitcoin protocol development discussions.