P2SH ScriptPubKey Structure

The beauty of P2SH lies in its minimalist locking script. Regardless of how complex the underlying smart contract is, the ScriptPubKey on the blockchain always looks exactly the same.

1. The Locking Script (ScriptPubKey)

A P2SH script follows this three-part template: OP_HASH160 [20-Byte Script Hash] OP_EQUAL

• OP_HASH160: Hashes whatever is on the top of the stack (the Redeem Script provided by the spender) using SHA256 + RIPEMD160.

• [20-Byte Hash]: The target provided by the sender.

• OP_EQUAL: Returns 1 if the hashes match, otherwise 0.

2. Raw Hex Representation

In a raw transaction, a P2SH script is very compact: a9 14 [20-byte-hash] 87

Hex	Opcode	Purpose
0x49	OP_HASH160	Hash the provided script
0x14	Push 20 Bytes	The length of the hash data
0x87	OP_EQUAL	Verify the hashes match

3. Comparison to P2PKH

You might notice that OP_HASH160 and a 20-byte hash are also used in P2PKH.

• In P2PKH, the hash is of a Public Key.

• In P2SH, the hash is of a Script (the Redeem Script).

4. The Hidden Logic

Because the script only contains a hash, a miner or observer cannot tell if the output is:

• A 2-of-3 Multisig.

• A Timelocked transaction (CLTV).

• A complex escrow script. This is a massive boost for Privacy and Fungibility, as all P2SH outputs look identical on the ledger.

In the next section, we will break down the Redeem Script and how to unlock a P2SH output.