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cryptoadvance / specter-diy

DIY airgapped hardware wallet that uses QR codes for communication with the host
MIT License
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import multisig wallet - "My key" not found - watch only #186

Closed chri2 closed 2 years ago

chri2 commented 2 years ago

I tried to import a multisig wallet per json and wondered why I always ended up with a watch only wallet.

Looking at the specter-diy master public key for multisig and one of the master public keys of the imported watch only wallet I found them to be the same.

Both start with [aabbccdd/48h/0h/0h/2h] followed by the same master public key.

The aabbccdd part differed in the both keys.

I didn't find reference to the format, but it seems that the aabbccdd part is kind of a serial number of the device the key has been generated on.

I edited my wallet.json to make that part match the part my specter-diy showed to me and imported the multisig wallet again.

This time specter-diy recognized that it had already the private key for that one public key and saved the multisig wallet - not as 'watch only', but as I'd expected as a normal wallet I could sign with.

My question is whether it wouldn't be better to ignore the suspected 'serial number' aabbccdd-'serial number'-part since it wouldn't be an unusual use case to import a multisig wallet to a replacement device already holding the correct private key. A replacement device would in most cases have a different aabbccdd-'serial number'-part I suspect.

stepansnigirev commented 2 years ago

aabbccdd is a fingerprint of the root key, not a serial number of the device. It helps the device to understand if this key belongs to the wallet or not. What software wallet do you use to import the multisig setup to DIY? Specter-Desktop or something else?

chri2 commented 2 years ago

Thanks and sorry for the disturbance. I guess I just didn't find the documentation how to build the []-derivation-part correctly. I had to add the []-part in front of a key manually to import a key to some wallet and it just worked with putting some values for the fingerprint in there and the correct derivation path. I then saved that key and reused it to test signatures on specter-diy. Thanks for clarifying! If you'd have any reference to the description of the []key-format at hand I'd be happy if you'd share it. I guess I failed twice in searching for it.

stepansnigirev commented 2 years ago

Check out key expressions in descriptors (bip-380): https://github.com/bitcoin/bips/blob/master/bip-0380.mediawiki#key-expressions

Fingerprint is the first 4 bytes of hash-160 of the root public key in hex. For example if you have a root key from mnemonic abandon*11 about, the root xprv is xprv9s21ZrQH143K3GJpoapnV8SFfukcVBSfeCficPSGfubmSFDxo1kuHnLisriDvSnRRuL2Qrg5ggqHKNVpxR86QEC8w35uxmGoggxtQTPvfUu, corresponding public key is 03d902f35f560e0470c63313c7369168d9d7df2d49bf295fd9fb7cb109ccee0494, it's hash160 is 73c5da0a03d2d0803b731f04242bb40ced2f8bbc and therefore the fingerprint is 73c5da0a. So to make sure your software wallet uses correct derivation path in PSBT you should include fingerprint and derivation like this: segwit xpub: [73c5da0a/84h/0h/0h]xpub6CatWdiZiodmUeTDp8LT5or8nmbKNcuyvz7WyksVFkKB4RHwCD3XyuvPEbvqAQY3rAPshWcMLoP2fMFMKHPJ4ZeZXYVUhLv1VMrjPC7PW6V and corresponding receiving descriptor will be

wpkh([73c5da0a/84h/0h/0h]xpub6CatWdiZiodmUeTDp8LT5or8nmbKNcuyvz7WyksVFkKB4RHwCD3XyuvPEbvqAQY3rAPshWcMLoP2fMFMKHPJ4ZeZXYVUhLv1VMrjPC7PW6V/0/*)
chri2 commented 2 years ago

Just to fill in the information: I ran into the issue, because I tried to generate a multisig wallet in specter using as one device an electrum wallet. On the electrum wallet I only got the xpub or Zpub not including the xfp which is needed by other software to import the xpub to form a multisig wallet. Long story short, I just added it. Later I played with the specter-diy and imported the seed from electrum to the specter-diy. On the specter-diy I tried to rebuild the multisig wallet using the data of electrum with a freely invented xfp which specter-diy correctly identified as not fitting its seed and derived keys.

Electrum has got an open issue related to this problem even though they only mention coldcard as a problematic device in a multisig setup. Will add the information there that their issue might also inflict problems when using specter-diy as a replacement for a former electrum wallet.