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Tapscript Multisig Output Script Descriptors

BIP 387. Pieter Wuille.

BIP 387, Tapscript Multisig Output Script Descriptors. This document specifies multi_a() and sortedmulti_a() output script descriptors.

Status in the source: Deployed. A reading of the public specification, not a copy of it and not a certification.

Tapscript Multisig Output Script Descriptors is worth reading for the rule it actually adds: This document specifies multi_a() and sortedmulti_a() output script descriptors.
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
6

Code

Source, repository, and what is actually hosted

  • BIP 387https://bips.dev/387
  • The source URL is not a GitHub repository. No code remote is invented.
  • Full text is not mirrored. Public availability is not a licence to copy the file onto this site.
  • Add to a reading list

01 Claim ledger

What the paper is allowed to say

Each row is a sentence already in the study. The status is the same on every row: a model claim, not a live measurement.

  1. Claim 01 · Paper model

    The rule

    This document specifies multi_a() and sortedmulti_a() output script descriptors.

  2. Claim 02 · Paper model

    What was already failing

    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.

  3. Claim 03 · Paper model

    What the number does not mean

    The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

  4. Claim 04 · Paper model

    What a builder should be able to point at

    An implementation either constrains multi_a, sortedmulti_a, KEY_1 or it is a different design.

02 Three cuts

Observation, model, falsifier

A desk does not stop at the summary. Each claim is cut three ways, using only this study's own assumptions and checks. Nothing here is a new figure.

  1. 01 The rule

    Observation

    What the study says

    This document specifies multi_a() and sortedmulti_a() output script descriptors.

    Model

    What has to hold

    The object that has to change is multi_a, sortedmulti_a, KEY_1. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    What is covered by the signed bytes in Tapscript Multisig Output Script Descriptors?

  2. 02 What was already failing

    Observation

    What the study says

    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.

    Model

    What has to hold

    The object that has to change is multi_a, sortedmulti_a, KEY_1. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    Can the same signature be replayed on another chain, account, or message?

  3. 03 What the number does not mean

    Observation

    What the study says

    The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

    Model

    What has to hold

    You are implementing BIP 387 at the status the text itself states: Deployed.

    Falsifier

    What would retire it

    Which primitive does the text require: multi_a, sortedmulti_a, KEY_1?

  4. 04 What a builder should be able to point at

    Observation

    What the study says

    An implementation either constrains multi_a, sortedmulti_a, KEY_1 or it is a different design.

    Model

    What has to hold

    The object that has to change is multi_a, sortedmulti_a, KEY_1. A neighbouring document with a similar name is not this one.

    Falsifier

    What would retire it

    Which primitive does the text require: multi_a, sortedmulti_a, KEY_1?

03 Sequence

One action, as an operating tape

  1. 01Open BIP 387 and read the status line before the examples.
  2. 02Write down the rule in one sentence. A fair version of that sentence is: This document specifies multi_a() and sortedmulti_a() output script descriptors.
  3. 03Name the object that changes: multi_a, sortedmulti_a, KEY_1.
  4. 04Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

04 Load-bearing

The argument, and where a pitch drops it

  1. What the text is allowed to settle

    The cut

    Bitcoin Improvement Proposal 387 can settle the shape of Tapscript Multisig Output Script Descriptors. It cannot settle whether a later client, a later fork, or a later wallet still does this.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    Wallet support is not the same as consensus validity.

  2. What this page will not pretend

    The cut

    There is no benchmark, no adoption number, and no claim that the mechanism is safe outside the assumptions written in the source.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    The source marks this deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

05 Register

What has to be true

  • Model · Not re-measured

    You are implementing BIP 387 at the status the text itself states: Deployed.

  • Cryptography · Not re-measured

    The object that has to change is multi_a, sortedmulti_a, KEY_1. A neighbouring document with a similar name is not this one.

  • Model · Not re-measured

    Wallet support is not the same as consensus validity.

06 Divergence

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.

A later client, parameter set, or reward formula is a different object. Cite this paper for the mechanism. Cite a primary release for the network. This desk has not re-run the proof.

07 Pre-mortem

What to check before you use the idea

  4. 0 of 3 marked on this browser. A mark is a reading note, not a pass, a rating, or a recommendation.

08 Anatomy

The paper, in the order a builder needs

The problem it 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 multi_a() and sortedmulti_a() output script descriptors.
  • Like BIP 383's multi() and sortedmulti() , both functions take a threshold and one or more public keys and produce a multisig script.
  • The primary distinction is that multi_a() and sortedmulti_a() only produce tapscripts and are only allowed in a tapscript context.

How the mechanism is specified

  • Taken from the specification, the next constraint is: Like BIP 383's multi() and sortedmulti() , both functions take a threshold and one or more public keys and produce a multisig script.
  • Locate multi_a, sortedmulti_a, KEY_1 in BIP 387 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 deployed. That is a statement about the text, not a promise that every wallet or node has shipped it.

Why the desk still reads it

Use BIP 387 when a pitch says 'Tapscript Multisig Output Script Descriptors' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.

09 Lexicon

Terms, opened into the record

BIP 387
The public text titled Tapscript Multisig Output Script Descriptors.
Deployed
The document's own label for how finished the text is. It is not a market fact.

10 Repository

Every linked record on this page

Underlined words open a page that already exists: a concept, a protocol profile, a failure record, or another paper. If a word is not underlined, this desk does not have a record for it.

Protocols

This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.

Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.