P2WPKH (Pay to Witness Public Key Hash)

In 2015, Pieter Wuille introduced a new feature to bitcoin called Segregated Witness or shorter, segwit. Basically, Segregated Witness move the proof of ownership from the scriptSig part of the transaction, to a new part called the witness of the input.

There is several reason to use this new scheme, here is a summary, for more details go to https://bitcoincore.org/en/2016/01/26/segwit-benefits/

• Third party Malleability Fix: Previously, a third party could change the transaction id of your transaction before it was confirmed. Not anymore.
• Linear sig hash scaling: Signing a transaction would require hashing the whole transaction for every input. This was a potential DDoS vector attack for large transactions.
• Signing of input values: The amount that is spent in an input is also signed, meaning the signer can’t be tricked about the amount of fee that is actually paid.
• Capacity increase: It will now be possible to have more than 1MB of transactions every 10 min, up to around 1.75.
• Fraud proof: Will be developed later, but SPV wallet will be able to validate more consensus rule than just following the longest chain.

Before the transaction signature belonged to the calculation of the transaction id, not anymore.

The signature contains the same information as a P2PKH spending, but is located in the witness instead of the scriptSig. The scriptPubKey though, is modified from

OP_DUP OP_HASH160 0067c8970e65107ffbb436a49edd8cb8eb6b567f OP_EQUALVERIFY OP_CHECKSIG

To

0 0067c8970e65107ffbb436a49edd8cb8eb6b567f

For nodes which did not upgrade, this looks like as two pushes on the stack. This means that any scriptSig can spend them. So even without the signatures, old nodes will consider such transactions valid. New nodes interprete the first push as the witness version and the second push as the witness program.

But new nodes will require the signature to get the transaction verified.

In NBitcoin, spending a P2WPKH output is not different from spending a normal P2PKH.
To get the ScriptPubKey to use from a public key, use PubKey.WitHash instead of PubKey.Hash.

var key = new Key();
Console.WriteLine(key.PubKey.WitHash.ScriptPubKey);

Which will output your something like

0 0067c8970e65107ffbb436a49edd8cb8eb6b567f

Signing the spending of such coin will be explained in the “Using the TransactionBuilder part”, and does not differ, in any way, from the code for signing a P2PKH output.

The witness, similar to the scriptSig of P2PKH, and the scriptSig empty:

"in": [
{
  "prev_out": 
    {
      "hash": "725497eaef527567a0a18b310bbdd8300abe86f82153a39d2f87fef713dc8177",
      "n": 0
    },
  "scriptSig": "",
  "witness": "3044022079d443be2bd39327f92adf47a34e4b6ad7c82af182c71fe76ccd39743ced58cf0220149de3e8f11e47a989483f371d3799a710a7e862dd33c9bd842c417002a1c32901 0363f24cd2cb27bb35eb2292789ce4244d55ce580218fd81688197d4ec3b005a67"
}

Once again, the semantic of P2WPKH is the same as the semantic of P2PKH, except that the signature is not placed at the same location as before.