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I'm not sure I understand the fields of my input. I have a P2SH address (Testnet). This is the input of my transaction:

  "vin": [
    {
      "txid": "a61389ff9af670770182198a984a4c1785625c60795bd57645ecc78765b23679",
      "vout": 1,
      "scriptSig": {
        "asm": "0014778daf651b21684b572644b47d551fce0ff71c74",
        "hex": "160014778daf651b21684b572644b47d551fce0ff71c74"
      },
      "txinwitness": [
        "3044022034a07f088dd88396cd378912a4ed6a156701b075f0facbbae810677048c390e602205df07e13bf4d56feece791a1b5e4d94bec9c93aae14bb87a1b4c6c54ae9bf2f701",
        "032c27921f2d15e7eca768c0e8a8b1aeb863328c74d6c194d41dde2888d4b0e75b"
      ],
      "sequence": 4294967295
    }
  ],

I understand that: in "asm" i have RedeemScript. In txinwitness i have my signature and the pubblic key. Correct?

Now, from the utxo used:

"txid": "a61389ff9af670770182198a984a4c1785625c60795bd57645ecc78765b23679",
    "vout": 1,
    "address": "2N7MaihNErbNH8XTkuZWtJYPzMQAWMPVKHd",
    "label": "",
    "redeemScript": "0014778daf651b21684b572644b47d551fce0ff71c74",
    "scriptPubKey": "a9149ac58ff47e27214b158b38da04bc8cbf72def14387",
    "amount": 0.01944571,
    "confirmations": 116,
    "spendable": true,
    "solvable": true,
    "desc": "sh(wpkh([7de694b7/0'/0'/7']032c27921f2d15e7eca768c0e8a8b1aeb863328c74d6c194d41dde2888d4b0e75b))#6z7uwusp",
    "safe": true

I deduce that I have used a P2SH-P2WPKH output. So in the ScriptPubkey I find the unlock condition (HASH160 of the public key of my address). In the redeem script I find HASH160 of the compressed public key 032c27921f2d15...

is it correct to say that, as an additional condition, to unlock a UTXO P2SH-P2WPKH, compared to a P2PKH, you need the HASH of an additional public key?

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I understand that: in "asm" i have RedeemScript. In txinwitness i have my signature and the pubblic key. Correct?

Correct. in a P2SH-P2WPKH the witness contains the signature and the public key, and the script signature contains the redeem script.

is it correct to say that, as an additional condition, to unlock a UTXO P2SH-P2WPKH, compared to a P2PKH, you need the HASH of an additional public key?

This is where you are kind of wrong.

The address of a P2SH-P2WPKH is the hash160 of the serialized redeem script of the P2WPKH, which has to be OP_0 <hash160_of_public_key> according to BIP0141. So it looks like you need an extra public key, but in reality you are just using the same public key twice. One that goes inside a redeem script to the script_signature, and another for the witness field that goes naked alongside the signature.

In other words, there is no extra public key. It's the same public key that is wrapped inside a smart contract (redeem script) defined by BIP0141, serialized, and then hashed. Now, this hash is the same hash used for the public keys (hash160), therefore the outputs of these smart-contract hashes have the same length of those public-key hashes, and that's why they can be confused with public keys when in reality they are smart contracts. This is done on purpose to make P2SH backward compatible .

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  • Therefore, the correct interpretation of the ScriptPubkey for a P2SH-P2WPKH address is "OP_HASH160 RedeemScript (= HASH160 Public Key) . Correct?
    – MaXbeMan
    Commented May 5, 2020 at 6:51
  • 1
    Almost. The script_pubkey would be "OP_HASH160 < HASH160 RedeemScript(= OP_0 <HASH160 Public Key>) > OP_EQUAL". You are omitting the "OP_0" in the redeem script (besides the OP_EQUAL in the script_pubkey). This OP_0 is very important because that is the pattern that will trigger the special rule in the nodes to process this as a segregated witness transaction, and not just as a regular P2SH transaction. This will allow the node to extract the signature and the public key from the witness field and to put it in the stack for final evaluation.
    – Oscar Serna
    Commented May 5, 2020 at 7:47

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