OP_CC: A simple introspection opcode to enable cheaper consolidations

The proposal of a new Tapscript opcode, named OP_CHECKCONSOLIDATION (OP_CC), is aimed at enhancing the efficiency of consolidation transactions within the Bitcoin network. This opcode introduces a method for making transactions that consolidate multiple Unspent Transaction Outputs (UTXOs) more space-efficient by altering how inputs from the same scriptPubKey (SPK) are processed. Specifically, OP_CC differentiates between the first transaction input spending a particular SPK and subsequent inputs doing the same. For the initial input, it behaves normally, but for the following inputs, it allows them to bypass individual signatures, relying instead on the signature provided for the first input.

This innovation allows for significant savings in terms of blockchain space. By utilizing OP_CC, each input beyond the first that spends from the same SPK does not require its own signature, reducing the required witness size dramatically. In a practical scenario involving a Taproot SPK with a single Tapscript leaf containing OP_CC, consolidating three UTXOs under this scheme would save 58 witness bytes per UTXO compared to traditional key-path spends. Normally, a key-path spend requires 65 bytes per input for the signature and related data, while a script-path spend with OP_CC needs only 36 bytes per input, including the script, control block, and associated lengths.

This approach not only simplifies the process of consolidating UTXOs but also contributes to a leaner, more efficient blockchain by reducing the amount of data needed for such transactions. The potential for scaling and efficiency improvements with OP_CC extends beyond simple examples, suggesting broader implications for transaction consolidation practices on the Bitcoin network.