PSBT_file.md

# Generally, each of the above (excluding Creator and Extractor) will simply add more and more data to a particular PSBT, until all inputs are fully signed. In a naive workflow, they all have to operate sequentially, passing the PSBT from one to the next, until the Extractor can convert it to a real transaction. In order to permit parallel operation, Combiners can be employed which merge metadata from different PSBTs for the same unsigned transaction.

The names above in bold are the names of the roles defined in BIP174. They're useful in understanding the underlying steps, but in practice, software and hardware implementations will typically implement multiple roles simultaneously.

PSBT

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+#PSBT Howto for Bitcoin Core
+Since Bitcoin Core 0.17, an RPC interface exists for Partially Signed Bitcoin Transactions (PSBTs, as specified in BIP 174).
+
+This document describes the overall workflow for producing signed transactions through the use of PSBT, and the specific RPC commands used in typical scenarios.
+
+#PSBT in general
+PSBT is an interchange format for Bitcoin transactions that are not fully signed yet, together with relevant metadata to help entities work towards signing it. It is intended to simplify workflows where multiple parties need to cooperate to produce a transaction. Examples include hardware wallets, multisig setups, and CoinJoin transactions.
+# Overall workflow
+Overall, the construction of a fully signed Bitcoin transaction goes through the following steps:
+
+<> A Creator proposes a particular transaction to be created. They construct a PSBT that contains certain inputs and outputs, but no additional metadata.
+<> For each input, an Updater adds information about the UTXOs being spent by the transaction to the PSBT. They also add information about the scripts and public keys involved in each of the inputs (and possibly outputs) of the PSBT.
+<> Signers inspect the transaction and its metadata to decide whether they agree with the transaction. They can use amount information from the UTXOs to assess the values and fees involved. If they agree, they produce a partial signature for the inputs for which they have relevant key(s).
+<> A Finalizer is run for each input to convert the partial signatures and possibly script information into a final scriptSig and/or scriptWitness.
+<> An Extractor produces a valid Bitcoin transaction (in network format) from a PSBT for which all inputs are finalized.