diff --git a/09_5_Testing_a_Bitcoin_Script.md b/09_3_Testing_a_Bitcoin_Script.md similarity index 100% rename from 09_5_Testing_a_Bitcoin_Script.md rename to 09_3_Testing_a_Bitcoin_Script.md diff --git a/09_3_Scripting_a_P2PKH.md b/09_4_Scripting_a_P2PKH.md similarity index 100% rename from 09_3_Scripting_a_P2PKH.md rename to 09_4_Scripting_a_P2PKH.md diff --git a/09_5_Scripting_a_P2WPKH.md b/09_5_Scripting_a_P2WPKH.md new file mode 100644 index 0000000..f87bba4 --- /dev/null +++ b/09_5_Scripting_a_P2WPKH.md @@ -0,0 +1,297 @@ +# 7.3: Scripting a P2PKH + +> :information_source: **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning. + +With a basic understanding of Bitcoin Scripting in hand, you can now easily analyze the functioning of a standard P2PKH script. + +## Understand the Unlocking Script + +We've long said that when funds are sent to a Bitcoin address, they're locked to the private key associated with that address. This is managed through the `scriptPubKey` of a P2PKH transaction, which is designed such that it requires the recipient to have the private key associated with the the P2PKH Bitcoin address. To be precise, the recipient must supply both the actual public key and a signature generated by the private key. + +That's what the `scriptSig` unlocking script seen in the previous section showed, a ` `: +`3045022100c4ef5b531061a184404e84ab46beee94e51e8ae15ce98d2f3e10ae7774772ffd02203c546c399c4dc1d6eea692f73bb3fff490ea2e98fe300ac6a11840c7d52b6166[ALL] 0319cd3f2485e3d47552617b03c693b7f92916ac374644e22b07420c8812501cfb`. + +## Understand the Locking Script + +The associated `scriptPubKey` locking script from the previous section was `OP_DUP OP_HASH160 371c20fb2e9899338ce5e99908e64fd30b789313 OP_EQUALVERIFY OP_CHECKSIG`, which is the standard locking methodology for a P2PKH address. That long string in the middle is a ``. + +## Run a P2PKH Script + +When you unlock a P2PKH UTXO, you (effectively) concatenate the unlocking and locking scripts, producing: +``` +Script: OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG +``` +Now, you can evaluate how the P2PKH UTXO is unlocked. + +First, you put the initial constants on the stack, then make a duplicate of the pubKey with `OP_DUP`: +``` +Script: OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG +Stack: [ ] + +Script: OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG +Stack: [ ] + +Script: OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG +Stack: [ ] + +Script: OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG +Running: OP_DUP +Stack: [ ] +``` +Why the duplicate? Because that's what's required by the script! + +Next, `OP_HASH160` pops the `` off the stack, hashes it, and puts the result back on the stack. +``` +Script: OP_EQUALVERIFY OP_CHECKSIG +Running: OP_HASH160 +Stack: [ ] +``` +Then, you place the `` that was in the locking script on the stack: +``` +Script: OP_EQUALVERIFY OP_CHECKSIG +Stack: [ ] +``` +`OP_EQUALVERIFY` is effectively two opcodes: `OP_EQUAL`, which pops two items from the stack and pushes `True` or `False` depending on if they're equal; and `OP_VERIFY` which pops that result and immediately marks the transaction as invalid if it's `False`. (Chapter 10 talks more about the use of `OP_VERIFY` as a conditional.) + +Assuming the two `es` are equal, you will have the following result: +``` +Script: OP_CHECKSIG +Running: OP_EQUALVERIFY +Stack: [ ] +``` +At this point you've proven that the `` supplied in the `scriptSig` hashes to the Bitcoin address in question, so you know that the redeemer knew the public key. They just need to prove knowledge of the private key, which is done with `OP_CHECKSIG`, which confirms that the unlocking script's signature matches that public key. +``` +Script: +Running: OP_CHECKSIG +Stack: [ True ] +``` +The Script now ends and the transaction is allowed to respend the UTXO in question. + + +## Running through a real example + +If you have a scriptPubKey (the script) and a signature and pubkey (the result of running the sigScript of the input), you can debug these by doing + +```Bash +$ btcdeb