Strict DER signatures

The five-minute read

One action, walked through

1. Open BIP 66 and read the status line before the examples.
2. Write down the rule in one sentence. A fair version of that sentence is: This document specifies proposed changes to the Bitcoin transaction validity rules to restrict signatures to strict DER encoding.
3. Name the object that changes: DER, OP_CHECKSIG, OP_CHECKSIGVERIFY.
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 66 at the status the text itself states: Deployed.
• The object that has to change is DER, OP_CHECKSIG, OP_CHECKSIGVERIFY. 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 Strict DER signatures, 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: DER, OP_CHECKSIG, OP_CHECKSIGVERIFY?

Terms

BIP 66

The public text titled Strict DER signatures.

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

• This document specifies proposed changes to the Bitcoin transaction validity rules to restrict signatures to strict DER encoding.
• Bitcoin's reference implementation currently relies on OpenSSL for signature validation, which means it is implicitly defining Bitcoin's block validity rules.
• Unfortunately, OpenSSL is not designed for consensus-critical behaviour (it does not guarantee bug-for-bug compatibility between versions), and thus changes to it can - and have - affected Bitcoin software.

How the mechanism is specified

• Taken from the specification, the next constraint is: Bitcoin's reference implementation currently relies on OpenSSL for signature validation, which means it is implicitly defining Bitcoin's block validity rules.
• Locate DER, OP_CHECKSIG, OP_CHECKSIGVERIFY in BIP 66 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 66 when a pitch says 'Strict DER signatures' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.