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6.3: Sending & Spending an Automated Multisig

The standard technique for creating multisignature addresses and for spending their funds is complex, but it's a worthwhile exercise for understanding a bit more about how they work, and how you can manipulate them at a relatively low level. However, Bitcoin Core has made multisigs a little bit easier in new releases.

⚠️ VERSION WARNING: The addmultisigaddress command is available in Bitcoin Core v 0.10 or higher.

Create a Multisig Address in Your Wallet

In order to make funds sent to multisig addresses easier to spend, you just need to do some prep using the addmultisigaddress command. It's probably not what you'd want to do if you were writing multisig wallet programs, but if you were just trying to receive some funds by hand, it might save you some hair-pulling.

Collect the Keys

You start off creating P2PKH addresses and retrieving public keys, as usual, for each user who will be part of the multisig:

machine1$ address3=$(bitcoin-cli getnewaddress)
machine1$ echo $address3
tb1q4ep2vmakpkkj6mflu94x5f94q662m0u5ad0t4w
machine1$ bitcoin-cli -named getaddressinfo address=$address3 | jq -r '.pubkey'
0297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc

machine2$ address4=$(bitcoin-cli getnewaddress)
machine2$ echo $address4
tb1qa9v5h6zkhq8wh0etnv3ae9cdurkh085xufl3de
machine2$ bitcoin-cli -named getaddressinfo address=$address4 | jq -r '.pubkey'
02a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f

Create the Multisig Address Everywhere

Next you create the multisig on each machine that contributes signatures using a new command, addmultisigaddress, instead of createmultisig. This new command saves some of the information into your wallet, making it a lot easier to spend the money afterward.

machine1$ bitcoin-cli -named addmultisigaddress nrequired=2 keys='''["'$address3'","02a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f"]'''
{
  "address": "tb1q9as46kupwcxancdx82gw65365svlzdwmjal4uxs23t3zz3rgg3wqpqlhex",
  "redeemScript": "52210297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc2102a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f52ae",
  "descriptor": "wsh(multi(2,[d6043800/0'/0'/15']0297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc,[e9594be8]02a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f))#wxn4tdju"
}

machine2$ bitcoin-cli -named addmultisigaddress nrequired=2 keys='''["0297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc","'$address4'"]'''
{
  "address": "tb1q9as46kupwcxancdx82gw65365svlzdwmjal4uxs23t3zz3rgg3wqpqlhex",
  "redeemScript": "52210297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc2102a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f52ae",
  "descriptor": "wsh(multi(2,[ae42a66f]0297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc,[fe6f2292/0'/0'/2']02a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f))#cc96c5n6"
}

As noted in the previous section, it currently doesn't matter whether you use addresses or public keys, so we've shown the other mechanism here, mixing the two. You will get the same multisig address either way. However, you must use the same order. Thus, it's best for the members of the multisig to check amongst themselves to make sure they all got the same result.

Watch for Funds

Afterward, the members of the multisig will still need to run importaddress to watch for funds received on the multisig address:

machine1$ bitcoin-cli -named importaddress address=2Mzw7WBvh9RAQ4ssKqxyNyP7L9NAojLqSW8 rescan="false"

machine2$ bitcoin-cli -named importaddress address=2Mzw7WBvh9RAQ4ssKqxyNyP7L9NAojLqSW8 rescan="false"

Respend with an Automated Transaction

Afterward, you will be able to receive funds on the multisignature address as normal. The use of addmultisigaddress is simply a bureaucratic issue on the part of the recipients: a bit of bookkeeping to make life easier for them when they want to spend their funds.

But, it makes life a lot easier. Because information was saved into the wallet, the signers will be able to respend the funds sent to the multisignature address exactly the same as any other address ... other than the need to sign on multiple machines.

You start by collecting your variables, but you no longer need to worry about scriptPubKey or redeemScript.

Here's a new transaction sent to our new multisig address:

machine1$ utxo_txid=b9f3c4756ef8159d6a66414a4317f865882ee04beb57a0f8349dafcc98f5acbc
machine1$ utxo_vout=0
machine1$ recipient=$(bitcoin-cli getrawchangeaddress)

You create a raw transaction:

machine1$ rawtxhex=$(bitcoin-cli -named createrawtransaction inputs='''[ { "txid": "'$utxo_txid'", "vout": '$utxo_vout' } ]''' outputs='''{ "'$recipient'": 0.00005}''')

Then you sign it:

machine1$ bitcoin-cli -named signrawtransactionwithwallet hexstring=$rawtxhex
{
  "hex": "02000000000101bcacf598ccaf9d34f8a057eb4be02e8865f817434a41666a9d15f86e75c4f3b90000000000ffffffff0188130000000000001600144f93c831ec739166ea425984170f4dc6bac75829040047304402205f84d40ba16ff49e60a7fc9228ef5917473aae1ab667dad01e113ca0fef3008b02201a50da2c65f38798aea94bcbd5bbf065bc1e38de44bacee69d525dcddcc11bba01004752210297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc2102a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f52ae00000000",
  "complete": false,
  "errors": [
    {
      "txid": "b9f3c4756ef8159d6a66414a4317f865882ee04beb57a0f8349dafcc98f5acbc",
      "vout": 0,
      "witness": [
        "",
        "304402205f84d40ba16ff49e60a7fc9228ef5917473aae1ab667dad01e113ca0fef3008b02201a50da2c65f38798aea94bcbd5bbf065bc1e38de44bacee69d525dcddcc11bba01",
        "",
        "52210297e681bff16cd4600138449e2527db4b2f83955c691a1b84254ecffddb9bfbfc2102a0d96e16458ff0c90db4826f86408f2cfa0e960514c0db547ff152d3e567738f52ae"
      ],
      "scriptSig": "",
      "sequence": 4294967295,
      "error": "CHECK(MULTI)SIG failing with non-zero signature (possibly need more signatures)"
    }
  ]
}

Note that you no longer had to give signrawtransactionwithkey extra help, because all of that extra information was already in your wallet. Most importantly, you didn't make your private keys vulnerable by directly manipulating them. Instead the process was exactly the same as respending a normal UTXO, except that the transaction wasn't fully signed at the end.

Sign It On Other Machines

The final step is exporting the partially signed hex to any other machines and signing it again:

machine2$ signedtx=$(bitcoin-cli -named signrawtransactionwithwallet hexstring=02000000014ecda61c45f488e35c613a7c4ae26335a8d7bfd0a942f026d0fb1050e744a67d000000009100473044022025decef887fe2e3eb1c4b3edaa155e5755102d1570716f1467bb0b518b777ddf022017e97f8853af8acab4853ccf502213b7ff4cc3bd9502941369905371545de28d0147522102e7356952f4bb1daf475c04b95a2f7e0d9a12cf5b5c48a25b2303783d91849ba421030186d2b55de166389aefe209f508ce1fbd79966d9ac417adef74b7c1b5e0777652aeffffffff0130e1be07000000001976a9148dfbf103e48df7d1993448aa387dc31a2ebd522d88ac00000000 | jq -r '.hex')

When everyone that's required has signed, you're off to the races:

machine2$ bitcoin-cli -named sendrawtransaction hexstring=$signedtx
3ce88839ac6165aeadcfb188c490e1b850468eff571b4ca78fac64342751510d

As with the shortcut discussed in §4.5: Sending Coins with Automated Raw Transactions, the result is a lot easier, but you lose some control in the process.

Summary: Sending & Spending an Automated Multisig

There's an easier way to respend funds sent to multisig addresses that simply requires use of the addmultisigaddress command when you create your address. It doesn't demonstrate the intricacies of P2SH respending, and it doesn't give you expansive control, but if you just want to get your money, this is the way to go.

What's Next?

Learn more about "Expanding Bitcoin Transactions" with Chapter Seven: Expanding Bitcoin Transactions with PSBTs.