OP_CHECKUTXOSETHASH idea

This soft fork suggestion would allow miners the option to embed a deterministic hash of the current Unspent Transaction Output (UTXO) set within a block. Though the inclusion of this hash would not be mandatory, its presence would necessitate verification by all nodes, with failure to do so resulting in block rejection. Blocks lacking this hash would remain valid, thus ensuring backward compatibility with older nodes, which would simply deem the new opcode unspendable. The proposal underscores that the computation of the full UTXO root is deliberately resource-intensive to align incentives properly, meaning miners are likely to generate these checkpoints only when the associated fees adequately cover the involved costs. To preclude abuse and uphold system efficiency, it's suggested that such checkpoint inclusions be capped at one per block, fostering a voluntary, fee-motivated mechanism that endorses consensus enforcement of checkpoints without mandating them for every mined block. This strategy aims to alleviate the demands on node resources both during initial syncs and regular operations by enabling most nodes to depend on a rolling history validated by sporadic high-value commitments, thereby reducing the network's overall resource footprint while still accommodating archival nodes that opt to store the entire blockchain.

Moonsettler raises concerns regarding the computational expense of nodes computing and the potential for denial-of-service (DOS) attacks within Bitcoin's development, suggesting a limitation of UTXO set commitments to every 2016 blocks to coincide with Bitcoin's difficulty adjustment epochs. This would involve committing to the UTXO set at the epoch's start or end, thereby avoiding disruption to mining operations. Moonsettler also points out the challenge scripts face in validation until they're included in a block, hinting at the possibility for transactions that might be invalid for mining to enter the mempool, thus requiring additional eviction steps. This situation could introduce new types of pinning attacks exploiting this vulnerability without incurring costs, leading Moonsettler to suggest addressing these concerns through a soft fork targeting the coinbase transaction structure rather than integrating this solution into the script directly.

Further discussions on the Bitcoin Development Mailing List have focused on optimizing network operations without sacrificing security or performance, particularly concerning the efficiency of validating block authenticity. A significant inefficiency noted is the requirement for each participant to individually recompute certain data to verify a block's validity. Peter Todd's work on delayed TXO commitments offers an expanded analysis of a proposed solution to this issue, emphasizing the use of the UTXO set root from prior intervals as a strategy for security and efficient synchronization without centralized checkpoint producers. Incremental hashing techniques and various data structures like Merkleized trees or accumulators such as Utreexo are mentioned as methods to enhance this process's efficiency, focusing updates only on changed UTXOs to hasten the procedure and reduce resource intensity.

Criticism has also been voiced against the idea of relying significantly on high-value commitments and archival nodes for preserving the complete chain, likening it to SPV (Simplified Payment Verification) and questioning its effectiveness in maintaining validation beyond majority hash power control. Concerns were raised about the economic viability and technical efficacy of implementing such a system, highlighting the need for a balance between innovation and preserving Bitcoin's foundational principles.