BIP: 384
  Layer: Applications
  Title: combo() Output Script Descriptors
  Author: Pieter Wuille <pieter@wuille.net>
          Ava Chow <me@achow101.com>
  Comments-Summary: No comments yet.
  Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0384
  Status: Final
  Type: Informational
  Created: 2021-06-27
  License: BSD-2-Clause

Abstract

This document specifies combo() output script descriptors. These take a key and produce P2PK, P2PKH, P2WPKH, and P2SH-P2WPKH output scripts if applicable to the key.

Copyright

This BIP is licensed under the BSD 2-clause license.

Motivation

In order to make the transition from traditional key based wallets to descriptor based wallets easier, it is useful to be able to take a key and produce the scripts which have traditionally been produced by wallet software.

Specification

A new top level script expression is defined: combo(KEY). This expression can only be used as a top level expression. It takes a single key expression as an argument and produces either 2 or 4 output scripts, depending on the key. A combo() expression always produces a P2PK and P2PKH script, the same as putting the key in both a pk() and a pkh() expression. If the key is/has a compressed public key, then P2WPKH and P2SH-P2WPKH scripts are also produced, the same as putting the key in both a wpkh() and sh(wpkh()) expression.

Test Vectors

Valid descriptors followed by the scripts they produce. Descriptors involving derived child keys will have the 0th, and 1st scripts in additional sub-bullets.

• combo(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1)
  • 2103a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bdac
  • 76a9149a1c78a507689f6f54b847ad1cef1e614ee23f1e88ac
  • 00149a1c78a507689f6f54b847ad1cef1e614ee23f1e
  • a91484ab21b1b2fd065d4504ff693d832434b6108d7b87
• combo(04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)
  • 4104a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235ac
  • 76a914b5bd079c4d57cc7fc28ecf8213a6b791625b818388ac
• combo([01234567]xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL)
  • 2102d2b36900396c9282fa14628566582f206a5dd0bcc8d5e892611806cafb0301f0ac
  • 76a91431a507b815593dfc51ffc7245ae7e5aee304246e88ac
  • 001431a507b815593dfc51ffc7245ae7e5aee304246e
  • a9142aafb926eb247cb18240a7f4c07983ad1f37922687
• combo(xprvA2JDeKCSNNZky6uBCviVfJSKyQ1mDYahRjijr5idH2WwLsEd4Hsb2Tyh8RfQMuPh7f7RtyzTtdrbdqqsunu5Mm3wDvUAKRHSC34sJ7in334/*)
  • Child 0
    • 2102df12b7035bdac8e3bab862a3a83d06ea6b17b6753d52edecba9be46f5d09e076ac
    • 76a914f90e3178ca25f2c808dc76624032d352fdbdfaf288ac
    • 0014f90e3178ca25f2c808dc76624032d352fdbdfaf2
    • a91408f3ea8c68d4a7585bf9e8bda226723f70e445f087
  • Child 1
    • 21032869a233c9adff9a994e4966e5b821fd5bac066da6c3112488dc52383b4a98ecac
    • 76a914a8409d1b6dfb1ed2a3e8aa5e0ef2ff26b15b75b788ac
    • 0014a8409d1b6dfb1ed2a3e8aa5e0ef2ff26b15b75b7
    • a91473e39884cb71ae4e5ac9739e9225026c99763e6687

Invalid descriptors

• combo() in sh : sh(combo(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))
• combo() in wsh : wsh(combo(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))
• Script in combo(): combo(pkh(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))

Backwards Compatibility

combo() descriptors use the format and general operation specified in 380. As this is a wholly new descriptor, it is not compatible with any implementation. However the scripts produced are standard scripts so existing software are likely to be familiar with them.

Reference Implementation

combo() descriptors have been implemented in Bitcoin Core since version 0.17.