CHECKSEQUENCEVERIFY

The five-minute read

One action, walked through

1. Open BIP 112 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 (CHECKSEQUENCEVERIFY) for the Bitcoin scripting system that in combination with BIP 68 allows execution pathways of a script to be restricted based on the age of the output being spent.
3. Name the object that changes: CHECKSEQUENCEVERIFY, NOP3, NOT.
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 112 at the status the text itself states: Deployed.
• The object that has to change is CHECKSEQUENCEVERIFY, NOP3, NOT. 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 deployed. That is a statement about the text, not a promise that every wallet or node has shipped it. 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 CHECKSEQUENCEVERIFY, 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: CHECKSEQUENCEVERIFY, NOP3, NOT?

Terms

BIP 112

The public text titled CHECKSEQUENCEVERIFY.

Deployed

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 (CHECKSEQUENCEVERIFY) for the Bitcoin scripting system that in combination with BIP 68 allows execution pathways of a script to be restricted based on the age of the output being spent.
• CHECKSEQUENCEVERIFY redefines the existing NOP3 opcode.
• When executed, if any of the following conditions are true, the script interpreter will terminate with an error: the stack is empty; or the top item on the stack is less than 0; or the top item on the stack has the disable flag (1 / Below flags apply in the context of BIP 68 / / If this flag set, CTxIn::nSequence is NOT interpreted as a relative lock-time.

How the mechanism is specified

• Taken from the specification, the next constraint is: CHECKSEQUENCEVERIFY redefines the existing NOP3 opcode.
• Locate CHECKSEQUENCEVERIFY, NOP3, NOT in BIP 112 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 deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

Why a venture studio still reads it

Use BIP 112 when a pitch says 'CHECKSEQUENCEVERIFY' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.