multi signature – Can I sign multisig transaction only with private key in a descriptor based wallet?

All public keys or redeem script/witness script is required to sign the transaction when spending bitcoin multisig UTXO.

An experiment to see if you can sign the transaction without public keys:

Run bitcoind -signet=1 -rpcport=38332 -rpcuser=user -rpcpassword=password

Create 3 wallets m1, m2 and m3

$ bitcoin-cli -named createwallet wallet_name=m1 descriptors=false

Get 3 public keys from each wallet:

$ bitcoin-cli -rpcwallet=m1 getnewaddress

tb1q8hz93lwkmzjq2yapxr6mnsfwjt5wvp2f5zgm98

$ bitcoin-cli -rpcwallet=m1 getaddressinfo tb1q8hz93lwkmzjq2yapxr6mnsfwjt5wvp2f5zgm98

{
  "address": "tb1q8hz93lwkmzjq2yapxr6mnsfwjt5wvp2f5zgm98",
  "scriptPubKey": "00143dc458fdd6d8a40513a130f5b9c12e92e8e60549",
  "ismine": true,
  "solvable": true,
  "desc": "wpkh([045471ed/0'/0'/1']039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716)#wht4f5zk",
  "iswatchonly": false,
  "isscript": false,
  "iswitness": true,
  "witness_version": 0,
  "witness_program": "3dc458fdd6d8a40513a130f5b9c12e92e8e60549",
  "pubkey": "039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716",
  "ischange": false,
  "timestamp": 1663309171,
  "hdkeypath": "m/0'/0'/1'",
  "hdseedid": "ccd54fe6a42efde5251f8443f1edd7ebcf25fefa",
  "hdmasterfingerprint": "045471ed",
  "labels": [
    ""
  ]
}

Create 2 of 3 multisig with the public keys:

$ bitcoin-cli createmultisig 2 "[\"039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716\",\"0359591df29bbcdb8fb2e4cde5d92ecc8c6698d9f0ab27f2f76938cdddc2323279\",\"037e44526a83fdb2c89de80356eeda1bbfdb3738a1b3b70c3c71ea95feaeec4046\"]"

{
  "address": "2N7WpySLj8bBGFrZE8hxQUm29ZCwaqz5FvT",
  "redeemScript": "5221039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716210359591df29bbcdb8fb2e4cde5d92ecc8c6698d9f0ab27f2f76938cdddc232327921037e44526a83fdb2c89de80356eeda1bbfdb3738a1b3b70c3c71ea95feaeec404653ae",
  "descriptor": "sh(multi(2,039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716,0359591df29bbcdb8fb2e4cde5d92ecc8c6698d9f0ab27f2f76938cdddc2323279,037e44526a83fdb2c89de80356eeda1bbfdb3738a1b3b70c3c71ea95feaeec4046))#jqk9dcqj"
}

Send 0.001 sBTC to multisig address using signet faucet: 0b30a06e2653b84b0b976559a0efc9018a6da2a4ea6c71c346496d2ac36e43b5

Create a PSBT to spend this UTXO:

$ bitcoin-cli createpsbt "[{\"txid\":\"0b30a06e2653b84b0b976559a0efc9018a6da2a4ea6c71c346496d2ac36e43b5\",\"vout\":1}]" "[{\"tb1qvl3a3l8ejuyk62qfz2kjjxdndcrk99ldxchqvx\":\"0.0009\"}]" 

cHNidP8BAFICAAAAAbVDbsMqbUlGw3Fs6qSibYoBye+gWWWXC0u4UyZuoDALAQAAAAD9////AZBfAQAAAAAAFgAUZ+PY/PmXCW0oCRKtKRmzbgdil+0AAAAAAAAA

You will get "complete": false in the output if you try signing it with any 2 wallets using walletprocesspsbt or individually sign, combine with combinepsbt followed by finalizepsbt
Import multisig address in m1, descriptor (has all public keys) in m2 and redeemscript in m3 wallet:

$ bitcoin-cli -rpcwallet=m1 importmulti '[{ "scriptPubKey": { "address": "2N7WpySLj8bBGFrZE8hxQUm29ZCwaqz5FvT" }, "timestamp":"now", "watchonly": true }]'

 [
   {
     "success": true
   }
 ]

$ bitcoin-cli -rpcwallet=m2 importmulti '[{ "desc": "sh(multi(2,039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716,0359591df29bbcdb8fb2e4cde5d92ecc8c6698d9f0ab27f2f76938cdddc2323279,037e44526a83fdb2c89de80356eeda1bbfdb3738a1b3b70c3c71ea95feaeec4046))#jqk9dcqj", "timestamp":"now", "watchonly": true }]'

 [
   {
     "success": true
   }
 ]

$ bitcoin-cli -rpcwallet=m3 importmulti '[{ "scriptPubKey": "a9149c85346a6ea0c2b6c6904e5c464df6ef84fe170587", "redeemscript": "5221039927842080cc4a22d2d4a63c13b3d9a66564e230775981f03976787afe6cf716210359591df29bbcdb8fb2e4cde5d92ecc8c6698d9f0ab27f2f76938cdddc232327921037e44526a83fdb2c89de80356eeda1bbfdb3738a1b3b70c3c71ea95feaeec404653ae", "timestamp":"now", "watchonly": true }]'

 [
   {
     "success": true
   }
 ]

Try signing it with m1 and m2 or m1 and m3. It won’t work.

$ bitcoin-cli -rpcwallet=m1 walletprocesspsbt cHNidP8BAFICAAAAAbVDbsMqbUlGw3Fs6qSibYoBye+gWWWXC0u4UyZuoDALAQAAAAD9////AZBfAQAAAAAAFgAUZ+PY/PmXCW0oCRKtKRmzbgdil+0AAAAAAAAA
{
  "psbt": "cHNidP8BAFICAAAAAbVDbsMqbUlGw3Fs6qSibYoBye+gWWWXC0u4UyZuoDALAQAAAAD9////AZBfAQAAAAAAFgAUZ+PY/PmXCW0oCRKtKRmzbgdil+0AAAAAAAEAcgIAAAABf9MjFLP83xBP8nl17j6VId+Y2UW/5seoLnxCqNnLOAcAAAAAAP7///8CMew0w1QGAAAWABRA3SSDttwD9s5g86KiG+bhufb1caCGAQAAAAAAF6kUnIU0am6gwrbGkE5cRk3274T+FwWH1qYBAAAA",
  "complete": false
}

$ bitcoin-cli -rpcwallet=m2 walletprocesspsbt cHNidP8BAFICAAAAAbVDbsMqbUlGw3Fs6qSibYoBye+gWWWXC0u4UyZuoDALAQAAAAD9////AZBfAQAAAAAAFgAUZ+PY/PmXCW0oCRKtKRmzbgdil+0AAAAAAAEAcgIAAAABf9MjFLP83xBP8nl17j6VId+Y2UW/5seoLnxCqNnLOAcAAAAAAP7///8CMew0w1QGAAAWABRA3SSDttwD9s5g86KiG+bhufb1caCGAQAAAAAAF6kUnIU0am6gwrbGkE5cRk3274T+FwWH1qYBAAAA
{
  "psbt": "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",
  "complete": false
}

However, it will work with m2 and m3:

$ bitcoin-cli -rpcwallet=m2 walletprocesspsbt cHNidP8BAFICAAAAAbVDbsMqbUlGw3Fs6qSibYoBye+gWWWXC0u4UyZuoDALAQAAAAD9////AZBfAQAAAAAAFgAUZ+PY/PmXCW0oCRKtKRmzbgdil+0AAAAAAAAA
{
  "psbt": "cHNidP8BAFICAAAAAbVDbsMqbUlGw3Fs6qSibYoBye+gWWWXC0u4UyZuoDALAQAAAAD9////AZBfAQAAAAAAFgAUZ+PY/PmXCW0oCRKtKRmzbgdil+0AAAAAAAEAcgIAAAABf9MjFLP83xBP8nl17j6VId+Y2UW/5seoLnxCqNnLOAcAAAAAAP7///8CMew0w1QGAAAWABRA3SSDttwD9s5g86KiG+bhufb1caCGAQAAAAAAF6kUnIU0am6gwrbGkE5cRk3274T+FwWH1qYBACICA1lZHfKbvNuPsuTN5dkuzIxmmNnwqyfy92k4zd3CMjJ5RzBEAiB1+POriSk9sPSZnMxkCE6oDKiLmYNW5KxuRN/q0nJJmgIgWM3ZX3ryJEDKhcyM4NI9wnLpMqkIXZwTueM33kYUysgBAQRpUiEDmSeEIIDMSiLS1KY8E7PZpmVk4jB3WYHwOXZ4ev5s9xYhA1lZHfKbvNuPsuTN5dkuzIxmmNnwqyfy92k4zd3CMjJ5IQN+RFJqg/2yyJ3oA1bu2hu/2zc4obO3DDxx6pX+ruxARlOuIgYDWVkd8pu824+y5M3l2S7MjGaY2fCrJ/L3aTjN3cIyMnkExzmGAiIGA35EUmqD/bLInegDVu7aG7/bNzihs7cMPHHqlf6u7EBGBIup2JAiBgOZJ4QggMxKItLUpjwTs9mmZWTiMHdZgfA5dnh6/mz3FgQ9xFj9AAA=",
  "complete": false
}

$ bitcoin-cli -rpcwallet=m3 walletprocesspsbt 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
{
  "psbt": "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",
  "complete": true
}

This transaction can be finalized and broadcasted:

$ bitcoin-cli finalizepsbt 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
{
  "hex": "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",
  "complete": true
}

$ bitcoin-cli sendrawtransaction 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

6f56b1b93a6053cb9e7b91ae4786a20f8d34f1d183022142c2fbf8a16d780766

Tx: 6f56b1b93a6053cb9e7b91ae4786a20f8d34f1d183022142c2fbf8a16d780766

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