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

==Abstract==

This document specifies <tt>combo()</tt> 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: <tt>combo(KEY)</tt>.
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 <tt>combo()</tt> expression always produces a P2PK and P2PKH script, the same as putting the key in both a <tt>pk()</tt> and a <tt>pkh()</tt> 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 <tt>wpkh()</tt> and <tt>sh(wpkh())</tt> expression.

==Test Vectors==

TBD

==Backwards Compatibility==

<tt>combo()</tt> descriptors use the format and general operation specified in [[bip-0380.mediawiki|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 Implemntation==

<tt>combo</tt> descriptors have been implemented in Bitcoin Core since version 0.17.