Mining Theory – How to make a coinbase? How to use witnesses?

adminDecember 13, 2023

BIP141 added a new rule called “witness appointments.” “Promises are written to the scriptPubKey of the Coinbase transaction,” the document states. I didn’t quite understand what it meant, so I directly placed ‘default_witness_commitment’ provided in the block template when creating Coinbase in the scriptPubKey location. Here is my code:

def makeCoinbase()->None:
    global coinbase,tmpl
    version=pack('<L',1)
    inputCount=unhexlify('01')
    txHash=unhexlify('0000000000000000000000000000000000000000000000000000000000000000')
    preSequence=unhexlify('ffffffff')
    eh=encodeHeight(tmpl('height'))  #Don't worry about this function, it handles height
    msg=eh+b'my message'
    msgSize=pack('B',len(msg))
    sequence=unhexlify('ffffffff')
    outCount=unhexlify('01')
    amount=pack('<Q',tmpl('coinbasevalue'))
    script=unhexlify(tmpl('default_witness_commitment'))
    scriptSize=pack('B',len(script))
    lockTime=unhexlify('00000000')
    coinbase=version+inputCount+txHash+preSequence+msgSize+msg+\
        sequence+outCount+amount+scriptSize+script+lockTime
    tmpl('transactions').insert(0,
        'data':coinbase.hex(),
        'txid':dblsha(coinbase)(::-1).hex()
    )

The tmpl variable is the template obtained using the “getblocktemplate” command. I am testing my code in regtest. When you submit a block, Bitcoin Core creates a new block. And my balance increased. However, when I checked Coinbase for the newly created block, the results were as follows.


    'txid': '9cb794f3292d1ece3af6c1d3055cf6fb26cf2126ff48b39b229bfec5ec651ec4', 
    'hash': 'de081b2a9552ac559d3501ed0669f675530fe9890e27d263c1aff65e678ddc4e', 
    'version': 1, 
    'size': 153, 
    'vsize': 126, 
    'weight': 504, 
    'locktime': 0, 
    'vin': (
        'coinbase': '016c54686520477265617420476f642050616e', 
        'txinwitness': ('0000000000000000000000000000000000000000000000000000000000000000'), 
        'sequence': 4294967295), 
    'vout': (
        'value': Decimal('50.00063100'), 
        'n': 0, 
        'scriptPubKey': 
            'asm': 'OP_RETURN aa21a9edb14717ddf39dacad0babfff4d8d951c076e95d11d2b1f328632c32f98c015d2c', 
            'desc': 'raw(6a24aa21a9edb14717ddf39dacad0babfff4d8d951c076e95d11d2b1f328632c32f98c015d2c)#psf60z3m', 
            'hex': '6a24aa21a9edb14717ddf39dacad0babfff4d8d951c076e95d11d2b1f328632c32f98c015d2c', 
            'type': 'nulldata'
        
    ), 
    'hex': '010000000001010000000000000000000000000000000000000000000000000000000000000000ffffffff13016c54686520477265617420476f642050616effffffff017ce8062a01000000266a24aa21a9edb14717ddf39dacad0babfff4d8d951c076e95d11d2b1f328632c32f98c015d2c0120000000000000000000000000000000000000000000000000000000000000000000000000'

As you can see, it only contains one vout. And that vout doesn’t contain any address. But if you look at Coinbase for a block on the main network, it always contains more than one vout, and the vout contains an address. My question is, am I building Coinbase the right way? If not, how do I fix it? Bitcoin Core did not report any errors, but I always suspected that I had lost the miner’s address.

adminDecember 13, 2023