Failed CHECK(MULTI)SIG operation - BIP143 hash pre-image

Question

Using Blockstream's api to broadcast a raw transaction to the Bitcoin testnet, I encountered the following error:

sendrawtransaction RPC error: {"code":-26,"message":"non-mandatory-script-verify-flag (Signature must be zero for failed CHECK(MULTI)SIG operation) (code 64)"}

I've noticed that many people have ran into a similar issue before. However, all of the proposed solutions didn't fix my issue. I've looked at the Bitcoin source code on Github and determined that the data I am committing to my hash for signing is incorrect.

Below is the hash pre-image that I'm creating for bip143 p2sh(p2wpkh).

    nVersion:     01000000
    hashPrevouts: 4f3c0f6726ec7f020da2a01598d1741225ea429a34bfdd4c4af2a1c9e45a9bed
    hashSequence: 3bb13029ce7b1f559ef5e747fcac439f1455a2ec7c5f09b72290795e70665044
    outpoint:     b9d615615976600739be12a67f326836e4256d7d1c4fe50163536ad8dd7647c301000000
    scriptCode:   1976a91499f27cf1ecb8c1a4c20bdbcdc7992cdb12c9ee5d88ac
    amount:       6981680000000000
    nSequence:    ffffffff
    hashOutputs:  57dbf9cb180c89fe35000b693ea089e521097e6d3f504cfec1620325fcec0036
    nLockTime:    00000000
    nHashType:    01000000

Answer 1

After a while of debugging, I was able to find the issue.

My previous assumption that I was committing the wrong data to the hash was correct.

The transaction ID that is needed to construct hashPrevouts and outpoint was incorrect. I needed to reverse the bytes of this value for the hash to be correct.

For example:

• b9d615615976600739be12a67f326836e4256d7d1c4fe50163536ad8dd7647c3 (a searchable txid on Bitcoin testnet)

becomes...

• c34776ddd86a536301e54f1c7d6d25e43668327fa612be39076076596115d6b9.

In summary, my advice would be to step through the interpreter and reevaluate your assumptions of all the data that you're committing to the hash for signing.

A little bit of code never hurts,

Typescript: Buffer.from(transactionId, "hex").reverse().toString("hex");