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I have some funds locked in a testnet P2SH address which requires 2-of-3 signatures.
This is the address: 2NEKRqUqoDtsELzpBa5wuWEiJeVbio5cSa2
and the 3 keys:

#1 - cU1mPkyNgJ8ceLG5v2zN1VkZcvDCE7VK8KrnHwW82PZb6RCq7zRq
#2 - cPTFNJD7hgbZTqNJgW89HABGtRzYo5aLpCQKvmNdtRNGWo49NAky
#3 - cNUe2L9CNJZoedMU8YNrzRuxFc56dvMjFxzK4mTsSGhXwbidAyog

The multisig script is: OP_2 <Key #1 length> <Key #1 PubKey> <Key #2 length> <Key #2 PubKey> <Key #3 length> <Key #3 PubKey> OP_3 OP_CHECKMULTISIG

I have also created a transaction spending the funds in this address, however I cannot broadcast this transaction because it gives the error Mempool accept test failed: 16: mandatory-script-verify-flag-failed (Signature must be zero for failed CHECK(MULTI)SIG operation).

Here is the transaction:

01000000  //Version
01        //Input Count
e29cf4dad1c36d5e316bac18edfc665f8323050d7260b94b72777b12a4eecba0  //TXID
00000000  //Out index
fb        //ScriptSig size
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     //ScriptSig (2 signatures followed by the redeem script)
ffffffff         //Sequence
01               //Output count
204e000000000000 //Output Value
16               //ScriptPubKey size
001491c6c31a62b37a16447ccf44224eb1ab78ca0299  //scriptPubKey (Segwit P2PKH)
00000000         //Locktime

Here are the steps I took to sign the input:

1. Hash the input with the scriptPubKey as the scriptSig and SigHash ALL appended
2. Sign the hashed signature with Key #1 and Key #2
3. Construct the scriptSig by concatenating the 2 signatures and redeem script
4. Place the scriptSig in the scriptSig field of the input

Im not sure if I am missing a step or have done a step incorrectly. I did pretty much the same steps as signing a P2PKH input which I can successfully create, just with different scriptSigs.

Any help would be appreciated.

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  • The signature verification seems to have failed. The calculation of the sighash used for the signature may be wrong. BTW, e29cf4dad1c36d5e316bac18edfc665f8323050d7260b94b72777b12a4eecba0 is tx hash, not TXID. If the endianness is reversed, it becomes TXID.
    – Shigeyuki Azuchi
    Commented Oct 4, 2021 at 1:11
  • I found where I went wrong. When creating the hashpreimage for the input, I was substituting in the scriptPubKey of the input instead of the redeemScript. When I used the redeemScript instead of the scriptPubKey, the signature was correct.
    – Keijyu
    Commented Oct 4, 2021 at 1:51
  • @Keijyu: You could add your last comment as an answer in the "Your Answer" section below - if you think it might help others in future, or delete the question if not.
    – RedGrittyBrick
    Commented Oct 4, 2021 at 9:01

1 Answer 1

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I found where I went wrong.

When creating the hashpreimage for the input, I was substituting in the scriptPubKey of the input instead of the redeemScript into the scriptSig.

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