Saturday, June 22, 2024

signature – What’s the transaction hash preimage for various values of SIGHASH (not SIGHASH_ALL) in P2PKH?

I’ve a couple of questions relating to the transaction hash preimage when signing with totally different values of the SIGHASH flag within the case of the P2PKH script.

I do know what the transaction hash preimage seems to be like in case of SIGHASH_ALL, however what does it appear like for different values of this flag.

So as an instance our transaction has 3 inputs and 4 outputs and we will denote it as T(I1, I2, I3; O1, O2, O3, O4), the preimage within the case of SIGHASH_ALL might be as follows.

Let’s begin with the enter. We take all inputs as they’re (its full content material). After that, we clear the scriptSig discipline of all inputs and set the size of the scriptSig discipline in all inputs to zero (0x00). Then, only for the enter we’re signing, we set its scriptSig discipline to the scriptPubKey from the output (UTXO) that this enter factors to. Additionally, we’ll set the size of the scriptSig discipline on this enter to the size of this newly added script scriptPubKey. The size of the scriptSig discipline in different inputs stays zero (0x00), and the scriptSig discipline stays empty. In relation to the outputs, we copy their full contents and add them to the beforehand described barely modified contents of the inputs. Lastly, we moreover append 0x01000000, which signifies that it’s a SIGHASH_ALL sort of signature.

That is the way it works within the case of SIGHASH_ALL, however how does it work for different values of this flag.

My assumption is that it’s precisely the identical course of, the one query is which inputs and outputs are taken into consideration. Subsequently, the transaction hash preimages for the totally different values of the SIGHASH flag are as follows (I took into consideration the values outlined within the Grasp Bitcoin e book):

  1. NONE (0x02) – Signature applies to all inputs, not one of the outputs

    • for inputs, completely the identical story that I described for SIGHASH_ALL applies
    • outputs will not be taken into consideration (they aren’t a part of the transaction hash preimage, comparable as scriptSig discipline of different inputs can also be not a component)
    • append 0x02000000 to the tip
  2. SIGNLE (0x03) – Signature applies to all inputs however solely the one output with the identical index quantity because the signed enter

    • for inputs, completely the identical story that I described for SIGHASH_ALL applies
    • solely the content material of the output whose index corresponds to the enter index is taken into consideration (eg if we wish to signal I2, we’ll take inputs I1, I2 and I3, however solely output O2)
    • append 0x02000000 to the tip
  3. ALL|ANYONECANPAY (0x81) – Signature applies to at least one enter and all outputs

    • solely the enter that we signal is included within the transaction hash preimage, the opposite inputs, i.e. their content material, will not be a part of the transaction hash preimage in any type (we simply ignore the opposite inputs, an analogous situation that we’d have if the transaction had just one enter and the SIGHASH_ALL)
    • for outputs, completely the identical story that I described for SIGHASH_ALL applies (we take the complete content material of all outputs)
    • append 0x81000000 to the tip
  4. NONE|ANYONECANPAY (0x82) – Signature applies to at least one enter, not one of the outputs

    • for inputs, completely the identical story that I described for 0x81 (ALL|ANYONECANPAY) applies
    • outputs will not be taken into consideration (they aren’t a part of the transaction hash preimage)
    • append 0x82000000 to the tip
  5. SINGLE|ANYONECANPAY (0x83) – Signature applies to at least one enter and the output with the identical index quantity

    • for inputs, completely the identical story that I described for 0x81 (ALL|ANYONECANPAY) applies
    • for outputs, completely the identical story that I described for 0x03 (SIGNLE) applies
    • append 0x83000000 to the tip

So my questions are:

1. Is that this the way it works?

2. Are there another values for the SIGHASH flag that I ought to cowl?

3. Is there some associated work/paper/customary that explains this (maybe for different scripts, like P2WPKH and so forth.)?

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