Bitcoin Script 101 (4): Step‑by‑Step P2PKH Walkthrough

This post walks through a classic P2PKH example so the “script + stack execution” model becomes concrete.

1) Locking Script (scriptPubKey)

OP_DUP OP_HASH160 <PubKeyHash> OP_EQUALVERIFY OP_CHECKSIG

Meaning:

• Duplicate the public key
• Hash and compare to the address hash
• Verify the signature if the hash matches

2) Unlocking Script (scriptSig)

<sig> <pubkey>

Meaning: provide signature and public key to prove ownership.

3) Concatenated Execution (Conceptual Steps)

Order: unlocking script first, then locking script.

Initial stack: empty

1. Push <sig>
2. Push <pubkey>
3. OP_DUP duplicates the pubkey
4. OP_HASH160 hashes the pubkey
5. Push <PubKeyHash>
6. OP_EQUALVERIFY compares hashes, fails if not equal
7. OP_CHECKSIG verifies signature with the pubkey

If the signature matches the transaction, the stack ends with true and the input is valid.

4) Summary

P2PKH’s core logic is simple:
“Give me a signature + pubkey → I verify you own the private key.”

Once this is clear, you can read P2SH, multisig, and Taproot scripts more easily.

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That’s the four‑part BTC Script 101 series. If you want, I can continue with multisig, timelocks (CLTV/CSV), and Taproot script paths.

Next: Back to Part 1 — Stack Model and Core Concepts