CTV
OP_CHECKTEMPLATEVERIFY
Links
Introduction
OP_CHECKTEMPLATEVERIFY (CTV) is a proposed new opcode that takes a commitment hash as a parameter
and requires any transaction executing the opcode include a set of outputs that match the
commitment. This makes it possible to create an address that specifies how any funds received to
that address may be spent — a design known in Bitcoin as a covenant.
Originally introduced under the name OP_CHECKOUTPUTSHASHVERIFY (COSHV) and later renamed
OP_SECURETHEBAG, the proposal initially focused on the ability to create congestion control
transactions where a spender pays a single address using CTV which, when confirmed to a suitable
depth, then assures several receivers that they can each be paid. This two-step process can probably
be used anywhere payment batching is an option but it can likely reduce fees even further than
payment batching.
Later versions of the proposal placed greater emphasis on other contracts and covenants that could be created using the new opcode, such as the ability to create channel factories, vaults, and coinjoin transactions in new ways that might simplify construction or reduce fees. Other authors have mentioned that the new opcode could possibly be used to allow users to trustlessly pool their funds together into a single UTXO in a way that would increase privacy.
The original proposal also emphasized other contracts and covenants that could be created using the new opcode, such as the ability to create channel factories, vaults, coinjoin transactions in new ways that might simplify construction or reduce fees, and described how the new opcode could possibly be used to allow users to trustlessly pool their funds together into a single UTXO in a way that would increase privacy. These other concepts have been described in further detail in subsequent works by a variety of authors.
Criticisms of the proposal have focused on it being too specific to the congestion control use case rather than providing a generic covenant capability.
Specification
This proposal has been specified in BIP-119.
Use Cases
For use cases that are enabled by CTV, we refer to the more general use case page of transaction templating, or to the summary table.