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doc: M-of-N multisig using descriptor wallets and PSBTs, as well as a signing flow

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Michael Dietz 2021-05-26 10:37:24 -04:00
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26
doc/descriptors.md
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@ -139,6 +139,32 @@ Key order does not matter for `sortedmulti()`. `sortedmulti()` behaves in the sa
as `multi()` does but the keys are reordered in the resulting script such that they
are lexicographically ordered as described in BIP67.
#### Basic multisig example
For a good example of a basic M-of-N multisig between multiple participants using descriptor
wallets and PSBTs, as well as a signing flow, see [this functional test](/test/functional/wallet_multisig_descriptor_psbt.py).
The basic steps are:
1. Every participant generates an xpub. The most straightforward way is to create a new descriptor wallet.
Avoid reusing this wallet for any other purpose. Hint: extract the wallet's xpubs using `listdescriptors`
and pick the one from the `pkh` descriptor since it's least likely to be accidentally reused (legacy addresses)
2. Create a watch-only descriptor wallet (blank, private keys disabled). Now the multisig is created by importing the two descriptors:
`wsh(sortedmulti(<M>,XPUB1/0/*,XPUB2/0/*,…,XPUBN/0/*))` and `wsh(sortedmulti(<M>,XPUB1/1/*,XPUB2/1/*,…,XPUBN/1/*))`
(one descriptor w/ `0` for receiving addresses and another w/ `1` for change). Every participant does this
3. A receiving address is generated for the multisig. As a check to ensure step 2 was done correctly, every participant
should verify they get the same addresses
4. Funds are sent to the resulting address
5. A sending transaction is created using `walletcreatefundedpsbt` (anyone can initiate this). It is simple to do this in
the GUI by going to the `Send` tab in the multisig wallet and creating an unsigned transaction (PSBT)
6. At least `M` users check the PSBT with `decodepsbt` and (if OK) signs it with `walletprocesspsbt`. It is simple to do
this in the GUI by Loading the PSBT from file and signing it
7. The signed PSBTs are collected with `combinepsbt`, finalized w/ `finalizepsbt`, and
then the resulting transaction is broadcasted to the network
8. Checks that balances are correct after the transaction has been included in a block
[The test](/test/functional/wallet_multisig_descriptor_psbt.py) is meant to be documentation as much as it is a functional test, so
it is kept as simple and readable as possible.
### BIP32 derived keys and chains
Most modern wallet software and hardware uses keys that are derived using

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doc/psbt.md
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@ -92,6 +92,9 @@ hardware implementations will typically implement multiple roles simultaneously.
#### Multisig with multiple Bitcoin Core instances
For a quick start see [Basic M-of-N multisig example using descriptor wallets and PSBTs](./descriptors.md#basic-multisig-example).
If you are using legacy wallets feel free to continue with the example provided here.
Alice, Bob, and Carol want to create a 2-of-3 multisig address. They're all using
Bitcoin Core. We assume their wallets only contain the multisig funds. In case
they also have a personal wallet, this can be accomplished through the