Output descriptors to specify custom derivations and change

[gabridome]

this is the actual way to specify the derivation of the key
{ "xpub": "xpub...", "index": 0, "derivationMode": "native_segwit", "birthday": "2017/08/29" } Which is straight, simple and compatible with data a user can get from Ledger Live. To make the application more future proof, It would be convenient to be able to specify somehow the Output Descriptor (https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md) of the watch-only wallet we are going to import into bitcoin core. It could cover:

1. Different derivations than bip44, bip49 or bip84
2. Internal addresses
3. In future also multisig configurations

Also importmulti RPC call in bitcoin core supports Output Descriptors and the future version of the wallet will be more and more "descriptor based". I would think something like:

  {
      "descriptor": "wpkh([18734cbe/84'/1'/0']tpubDAZhhJ9SaAKCt2gngU8aA2babxVAM93oBgo2wGknMUDmtLrzvLnynFuAYo4eME3MqWpcTM3DpGL9J45nQw7CA7VroAY8e7v9Zo6r7mddUMS/0/*)#4c563hxu",
      "index": 0,
      "birthday": "2017/08/29"
    }

[onyb]

Thanks for your feedback @gabridome. It's a great suggestion indeed.

We actually already import output descriptors (see this). The descriptors, however, are constructed from the xpub, index, and derivationMode. To be fair, this is really brittle and much more error-prone than what you suggest.

I think specifying output descriptors in the config is not so user friendly, and easy to get wrong if you don't understand the schema. So for me, it needs to be complemented with displaying the receive and change descriptors directly on Ledger Live, in the account details section, so users can just copy-paste it in the config.

[gabridome]

So for me, it needs to be complemented with displaying the receive and change descriptors directly on Ledger Live, in the account details section, so users can just copy-paste it in the config.

I agree and will try to suggest it.

Il giorno lun 15 giu 2020 alle ore 12:02 Anirudha Bose < notifications@github.com> ha scritto:

Thanks for your feedback @gabridome https://github.com/gabridome. It's a great suggestion indeed.

We actually already import output descriptors (see this https://github.com/onyb/ledger-sats-stack/blob/634dc011dda2f7c0bc12cbfe478360315457b12e/bus/wallet.go#L91-L98). The descriptors, however, are constructed from the xpub, index, and derivationMode. To be fair, this is really brittle and much more error-prone than what you suggest.

I think specifying output descriptors in the config is not so user friendly, and easy to get wrong if you don't understand the schema. So for me, it needs to be complemented with displaying the receive and change descriptors directly on Ledger Live, in the account details section, so users can just copy-paste it in the config.

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[onyb]

@gabridome In your example config, you used only the external chain, i.e. 0, in the output descriptor.

wpkh([18734cbe/84'/1'/0']tpubDAZhhJ9SaAKCt2gngU8aA2babxVAM93oBgo2wGknMUDmtLrzvLnynFuAYo4eME3MqWpcTM3DpGL9J45nQw7CA7VroAY8e7v9Zo6r7mddUMS/0/*)#4c563hxu

This also means that we'll need to add another output descriptor in the JSON config for the change path, i.e. 1, which seems repetitive to me. Do you think it is a problem to have two config entries per account, or is it better to be explicit even at the cost of some repetition?

[onyb]

This has been fixed in https://github.com/onyb/ledger-sats-stack/commit/f1677b44df05152eaacae099b8c3842ce9aa193f, and available in v0.4.0-alpha. The descriptor will be available on Ledger Live in a future release.

The configuration is now purely based on output descriptors. Here's an example of the new config format:

{
  "accounts": [
    {
      "descriptor": "wpkh([18734cbe/84'/1'/0']tpubDAZhhJ9...7mddUMS)#4c563hxu",
      "birthday": "2020/01/01"
    }
  ],
  "rpcurl": "localhost:8332",
  "rpcuser": "user",
  "rpcpass": "pass",
  "notls": true
}

Notice that the descriptor now describes the account rather than the address path, hence there needs to be only one entry per account, to answer my own question in the previous comment.

[gabridome]

Notice that the descriptor now describes the account rather than the address path, hence there needs to be only one entry per account, to answer my own question in the previous comment.

Yeah. Sorry for the late reply.

I would have been very explicit with something like:

{
  "accounts": [
    {
      "external": "wpkh([18734cbe/84'/1'/0']tpubDAZhhJ9...7mddUMS/0/*)#xxxxxxxx", # obviously the checksum don't match
      "internal": "wpkh([18734cbe/84'/1'/0']tpubDAZhhJ9...7mddUMS/1/*)#xxxxxxxx",
      "birthday": "2020/01/01"
    }
  ],
  "rpcurl": "localhost:8332",
  "rpcuser": "user",
  "rpcpass": "pass",
  "notls": true
}

But I think that even if the solution you choose is not perfect (it doesn't define the whole path) at least is not "wrong".

We can see in the future what decisions will be taken at the "Ledger Live Level" to rethink about the issue.

[onyb]

Reopening this issue, because your suggestion is quite cool! 👍

It's always better to have the exact descriptors that'll be imported in the config file. The account-level descriptor is more convenient (less no. of characters), but is less transparent.

[onyb]

Fixed in v0.5.0-alpha. Thanks for your valuable feedback!