P2TR ScriptPubKey Structure

The Taproot locking script is the pinnacle of minimalist design. It doesn't contain hashes or complex opcodes; it simply presents a single public key and tells the validator which version of the rules to apply.

1. The Locking Script (ScriptPubKey)

A P2TR script is exactly 34 bytes long: 51 20 [32-Byte Tweaked Public Key]

• 0x51: This is the opcode for OP_1. It signals that this output uses Witness Version 1.

• 0x20: The push-data opcode for 32 bytes (hex 0x20).

• [32-Byte Public Key]: Known as the Output Key (Q).

2. Why 32 bytes instead of 33?

Legacy and SegWit public keys are 33 bytes (1 byte prefix + 32 byte X-coordinate).

• Taproot uses Schnorr Signatures, which only require the X-coordinate.

• The 'parity' of the Y-coordinate is handled by the Schnorr math, allowing us to drop 1 byte from every public key on the blockchain.

3. The "Tweaked" Key

The 32-byte key in the script is not just a standard public key. It is a Tweaked Key (Q). Q = P + h(P, m)G

• P: The "Internal Key" (the base public key).

• m: The root of a Merkle tree containing hidden scripts.

• h: A cryptographic hash. This math allows the single key Q to "commit" to an entire tree of scripts without revealing any of them.

4. No Hashing

Notice that unlike P2WPKH or P2WSH, Taproot does not store a hash of the key. It stores the Public Key itself.

• This is safe because the public key is already a 32-byte value.

• It saves the step of hashing during validation, making Taproot spends slightly more efficient for nodes to process.

Attribute	P2WSH (V0)	P2TR (V1)
Witness Version	0x00	0x51 (OP_1)
Data Length	32 Bytes	32 Bytes
Data Type	Hash of Script	The Tweaked Public Key
Key Type	ECDSA (33b)	Schnorr (32b)

In the next section, we will explore the Key Path vs. Script Path spending mechanisms.