A "Free" Relay Attack Taking Advantage of The Lack of Full-RBF In Core

The proposed Bitcoin Improvement Proposal (BIP) for the Transaction Output for Contract Upgradeability (TRUC) has sparked a notable discussion within the Bitcoin community, particularly among those utilizing Child Pays For Parent in Coinjoin Outputs (CPFP-CO), such as Lightning Network (LN) anchor channels. The essence of this BIP is its opt-in nature, requiring users to adopt a new commitment transactions format. This transition, however, necessitates the closing and reopening of all LN anchor channels, presenting a significant obstacle due to the need for widespread user software upgrades. Such a requirement could severely delay the implementation of cluster mempool, contingent on the universal upgrade of LN users' software.

In efforts to mitigate these challenges, there has been considerable debate and exploration into an alternative approach involving imbued semantics for TRUC that can be applied retroactively to existing LN-style anchor outputs. This method would circumvent the need for immediate software upgrades, thereby allowing for the seamless introduction of cluster mempool functionality without necessitating widespread user action. The discussions and analyses concerning this imbued-semantics version of TRUC suggest a promising avenue for facilitating easier adoption and integration within the existing LN infrastructure.

For further details, the specifications and discussions around these proposals are documented and available for review. The original specification for the proposed BIP can be found on GitHub at this link, and an analysis of the imbued semantics approach is available at DelvingBitcoin.org. These resources provide in-depth insight into the technical considerations and potential impacts of the TRUC proposal on the Bitcoin ecosystem, specifically regarding LN operations and the broader implications for transaction output upgradeability.