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Lesson 14 / 21 · Advanced

PSBT: separate construction from signing

Follow a portable transaction through distinct responsibilities.

14 MIN WITH PRACTICEREAD → TRY → REFLECTNO WALLET NEEDED

By the end, you’ll be able to…

  • Identify the main PSBT roles.
  • Explain why a signer must still review the transaction.
Your learning map

Three questions to carry into this lesson.

01Identify the main PSBT roles.
02Explain why a signer must still review the transaction.
Use these goals to guide your reading. Try the paper exercise, then explain the result in your own words.

A container for collaboration

A Partially Signed Bitcoin Transaction carries a proposed transaction and supporting data so multiple tools can participate. BIP 174 describes roles such as creator, updater, signer, combiner, finalizer and extractor. One application may perform several roles, but the separation helps explain where data is added and where spending authorization occurs.

Portable does not mean trustworthy

A coordinator can prepare a PSBT without being allowed to spend. A signer must check the transaction and sufficient supporting information rather than assuming the coordinator is honest. Combining signatures does not authorize a different economic purpose. The final extracted transaction still needs broadcast and reconciliation; a complete signature set is not a confirmation.

Design for refusal and recovery

In a fictional two-person treasury, one person prepares a payment request and two authorized signers review their own displays. A mismatch stops the workflow. Logs can preserve the approved purpose and final transaction identifier without storing private keys. Test the recovery path if the coordinator disappears: can another compatible tool reconstruct the policy and complete the process? This lesson does not ask you to sign or upload any real PSBT.

Your turn / A paper experiment

Practice on paper

A coordinator says a PSBT is “ready.” Name three checks a signer should understand before authorizing it.

I’ve tried it — show the worked answer

Check recipient outputs and amounts, correct recognition of change, and the fee/network/policy context. The exact review depends on the wallet and script. “Ready” is a workflow label, not proof that the proposal matches human intent.

Want to explore with buttons and instant feedback? Try the practice lab ↗

Think it through

Make a choice. Discover why.

Choose an answer and check the explanation. You can retry as often as you like. These are practice questions, not a test of mastery; answers are not saved or sent.

1. Does a PSBT require the coordinator to hold private keys?
  • Yes
  • No
Read the explanation

No. Construction and signing can be separated.

2. Does finalizing a PSBT prove on-chain settlement?
  • Yes
  • No
Read the explanation

No. Broadcast and settlement checks come afterward.

One idea to take with you

Keep preparation, authorization and settlement independently understandable.

Your learning, at your pace

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