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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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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 as `multi()` does but the keys are reordered in the resulting script such that they
are lexicographically ordered as described in BIP67. 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 ### BIP32 derived keys and chains
Most modern wallet software and hardware uses keys that are derived using 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 #### 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 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 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 they also have a personal wallet, this can be accomplished through the