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I managed to create a raw tx using Bitcoinj but not able to figure out how to verify its signatures. Assuming I know the addresses corresponding to the (supposedly) unspent outputs used as inputs to the Tx, what is the easiest way to verify the Tx?

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You're interested in the following API calls:

public List<TransactionInput> Transaction.getInputs()
public Script TransactionInput.getScriptSig() throws ScriptException
public void Script.correctlySpends(Transaction txContainingThis, long scriptSigIndex, Script scriptPubKey)

Use them like so:

Transaction tx = ...
List<TransactionInput> inputs = tx.getInputs();
for(int i = 0; i < inputs.size(); i++) {
    TransactionInput input = inputs.get(i);
    Script scriptSig = input.getScriptSig();
    Script scriptPubKey = ...
    scriptSig.correctlySpends(tx, i, scriptPubKey);
}

The tricky bit is getting scriptPubKey. If you have the transactions you're spending in memory, it's as simple as input.getConnectedOutput().getScriptPubKey();

If it isn't, then you can make an educated guess by converting the address to a P2PKH scriptPubKey.

public static Script ScriptBuilder.createOutputScript(Address to)

This creates an edge case where if someone tries to spend a P2PK output, it will appear to be signed incorrectly to your program. (Both are represented by addresses.)

  • Seems to answer the question. Will check and revert. Thanks for mentioning the P2PK outputs. The transactions are created by me and are standard so I can probably ignore this. – Jus12 Jan 8 '15 at 5:22
  • correctlySpends requires a 4th boolean parameter (enforceP2SH). What is that? – Jus12 Jan 11 '15 at 5:07
  • @Jus12 It's for implementing a rare edge case of BIP0016. Set it to true. P.S. You are using an old version of BitcoinJ. You should update it. – Nick ODell Jan 11 '15 at 5:17
  • Thanks. I set it to true. There are significant changes from 0.11 to 0.12. I tried to upgrade but it breaks my code (requires some refactoring). Will get to it eventually. Are there any serious issues in using 0.11? – Jus12 Jan 12 '15 at 5:18
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    As an update, there are actually some serious in using 0.11 based on this bug report: github.com/bitcoinj/bitcoinj/issues/1082 – Jus12 Oct 15 '15 at 7:07

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