[Bug] Multi-sig on Sparrow Wallet

[Bastien-Satochip]

Reported on Telegram by user "JR":

Creating a multisig in sparrow wallet (2of3), let's say I do it with 3 Satochip cards and it goes alright. When finalized sparrow shows the output descriptor and warns the need to save it as multisig 2of3 means we can sign with two keys always that we also provide the output descriptor (if we don't have it, shall use the 3 keys to compose the wallet and then, 2of3 for signing). I save that output descriptor, in text and qr.

Now the wallet works perfectly, being able to sign transactions with no problem.

Now let's say I delete the wallet, I distribute the 3 Keys to 3 persons so every person has one key and one copy of the output descriptor.

At any other moment let's imagine 2 of the 3 keys meet together and want to operate with the wallet. They download sparrow, create new wallet and introduce the output descriptor. The wallet loads correctly, shows addresses, balances, utxo... All seems good.

Now is where problem happens. Trying to create a transaction, every seems good, but when signing with either one of the cards, an error appears and the signing fails. Later I will show you an screenshot if needed. I could reproduce this issue many times, was never possible to sign. Only with wallets constructed with the 3 keys don't give this error.

[Toporin]

I was able to reproduce the issue by doing the following:

• create new wallet
• import a multisig 2of3 descriptor
• Do not configure the keystores in settings, so they remain configured as watch only.
• Create a new transaction.
• When signing the transaction, a window opens to check for hardware wallet and if a Satochip is found, it tries to sign tx with it, but since the keystores are not configured as satochip, the 'fullpath' variable remains undefined, leading to the error.

A patch has been submitted (sparrowwallet/sparrow#1591) to avoid this error even if the keystores are not configured.

Without the patch, user can avoid this error by configuring at least one keystore as Satochip.