CHECKTEMPLATEVERIFY

The five-minute read

One action, walked through

1. Open BIP 119 and read the status line before the examples.
2. Write down the rule in one sentence. A fair version of that sentence is: A new opcode, OP_CHECKTEMPLATEVERIFY, to be activated as a change to the semantics of OP_NOP4.
3. Name the object that changes: OP_CHECKTEMPLATEVERIFY, OP_NOP4, NOP.
4. Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

The argument, unpacked

What has to be true

• You are implementing BIP 119 at the status the text itself states: Draft.
• The object that has to change is OP_CHECKTEMPLATEVERIFY, OP_NOP4, NOP. A neighbouring document with a similar name is not this one.
• Activation is a separate mechanism from the opcode or the sighash. This page does not pick a height.

What happened after the paper

The source marks this draft. It is not a live consensus rule just because it has a number. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

What to check before you use the idea

• Which bytes become invalid under CHECKTEMPLATEVERIFY, and which old transactions stay valid?
• Is enforcement in consensus, or only in the mempool policy of one client?
• Which of these objects does the text actually define: OP_CHECKTEMPLATEVERIFY, OP_NOP4, NOP?

Terms

BIP 119

The public text titled CHECKTEMPLATEVERIFY.

Draft

The document's own label for how finished the text is. It is not a market fact.

The problem the paper names

Bitcoin script and block validity only change when a soft fork says an old pattern is now invalid. Without that rule, every node is free to accept what this document wants to reject.

What the design proposes

• A new opcode, OP_CHECKTEMPLATEVERIFY, to be activated as a change to the semantics of OP_NOP4.
• OP_CHECKTEMPLATEVERIFY uses opcode OP_NOP4 (0xb3) as a soft fork upgrade.
• OP_CHECKTEMPLATEVERIFY does the following: There is at least one element on the stack, fail otherwise The element on the stack is 32 bytes long, NOP otherwise The DefaultCheckTemplateVerifyHash of the transaction at the current input index is equal to the element on the stack, fail otherwise The DefaultCheckTemplateVerifyHash commits to the serialized version, locktime, scriptSigs hash (if any non-null scriptSigs), number of inputs, sequences hash, number of outputs, outputs hash, and currently executing input index.

How the mechanism is specified

• Taken from the specification, the next constraint is: OP_CHECKTEMPLATEVERIFY uses opcode OP_NOP4 (0xb3) as a soft fork upgrade.
• Locate OP_CHECKTEMPLATEVERIFY, OP_NOP4, NOP in BIP 119 and apply it to one transaction or call.
• Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

• A soft fork does not bind a node that never upgrades. It binds the nodes that enforce the new rejection.
• Activation is a separate mechanism from the opcode or the sighash. This page does not pick a height.
• The source marks this draft. It is not a live consensus rule just because it has a number.

Why a venture studio still reads it

Use BIP 119 when a pitch says 'CHECKTEMPLATEVERIFY' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.