Create PSBT from a Transaction

[andreasgriffin]

Describe the enhancement

psbt.finalize() creates Tx from a PSBT. I would like to be able to reverse this, given the corresponding wallet is available. I am not sure this is possible, but would be great for the use case below.

PSBT.from_tx(transaction: Transaction, wallet:Wallet)->PSBT

Use case

• A finalizes multisig transaction contains signatures. However it is not clear which signer (fingerprint) created which signatures. A PSBT has however this association of fingerprints with signature: Feature request: PSBT (missing) signature info bdk-ffi#419
  • Why would one like to do this identification? Because that allows one to check when a signer was last able to sign. This gives a health status for each signer.
  • Why not get it from the PSBT directly? Because the last hardware signer typically finalizes the tx to have a smaller QR code. (Or the final tx is broadcasted another method via push_tx for example)

[nymius]

The clearance of the bip32_derivation or tap_key_origin, or any other fields is a requirement from BIP 174:

All other data except the UTXO and unknown fields in the input key-value map should be cleared from the PSBT.

I had a similar issue for silent payments.
I need the witness as well as the key source information. To accomplish it I sign, then finalize, then use miniscript planning module to replenish those fields with key source data and finally call the function to derive the silent payments¹.
Maybe some of this helps you. Have in mind that this flow is intended for a single party flow.
For your case, I guess the planning module doesn't work, so I would recommend if possible to clone the psbt before finalization and later match the data between the finalized and unfinalized psbts.

Footnotes

1. https://github.com/bitcoindevkit/bdk-sp/blob/master/silentpayments/tests/integration_tests/psbt.rs#L126-L131 ↩