Derivation Scheme for MuSig2 Aggregate Keys

The five-minute read

One action, walked through

1. Open BIP 328 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 how BIP 32 extended public keys can be constructed from a BIP 327 MuSig2 aggregate public key and how such keys should be used for key derivation.
3. Name the object that changes: SHA256.
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 328 at the status the text itself states: Complete.
• The object that has to change is SHA256. A neighbouring document with a similar name is not this one.
• Wallet support is not the same as consensus validity.

What happened after the paper

The source marks this complete. 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

• What is covered by the signed bytes in Derivation Scheme for MuSig2 Aggregate Keys?
• Can the same signature be replayed on another chain, account, or message?
• Which primitive does the text require: SHA256?

Terms

BIP 328

The public text titled Derivation Scheme for MuSig2 Aggregate Keys.

Complete

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

The problem the paper names

A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

What the design proposes

• This document specifies how BIP 32 extended public keys can be constructed from a BIP 327 MuSig2 aggregate public key and how such keys should be used for key derivation.
• Multiple signers can create a single aggregate public key with MuSig2 that is indistinguishable from a random public key.
• The cosigners need a method for generating additional aggregate pubkeys to follow the best practice of using a new address for every payment.

How the mechanism is specified

• Taken from the specification, the next constraint is: Multiple signers can create a single aggregate public key with MuSig2 that is indistinguishable from a random public key.
• Locate SHA256 in BIP 328 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 signature scheme is not a privacy system. It hides the signer only if the protocol says so.
• Wallet support is not the same as consensus validity.
• The source marks this complete. 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 328 when a pitch says 'Derivation Scheme for MuSig2 Aggregate Keys' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.