P2TR: Pay-to-Taproot (BIP 341)

P2TR (Pay-to-Taproot) is the most significant upgrade to Bitcoin scripting since SegWit. Activated in November 2021, it introduced a new way to handle transactions that maximizes privacy, efficiency, and flexibility. It is the first use of Witness Version 1 and utilizes the Bech32m address format.

1. The Great Unification

Before Taproot, it was easy for a block explorer to tell the difference between a single person (P2WPKH) and a complex multisig setup (P2WSH).

• Taproot changes this. In P2TR, every output looks like a single 32-byte public key.

• Whether you are a single user or a 100-key multisig wallet, your address starts with bc1p and looks identical to everyone else's.

2. Key Technologies

Taproot is powered by three major technical pillars:

1. Schnorr Signatures (BIP 340): A more efficient and mathematically elegant alternative to ECDSA.

2. MAST (Merkleized Abstract Syntax Trees): A way to compress multiple spending conditions into a single hash.

3. Tapscript: An updated version of the Bitcoin Script language specifically for Taproot outputs.

3. Privacy by Default

In legacy multisig, you have to reveal the names (public keys) of everyone in your group when you spend. In Taproot, if everyone in the group agrees to the transaction, you can "Aggregate" your signatures into a single signature. The blockchain only sees one person signing, providing massive privacy for collaborative custody.

4. The bc1p Addresses

Taproot addresses start with the prefix bc1p.

• The 'p' represents Witness Version 1.

• They use the Bech32m encoding, which fixed a minor checksum vulnerability found in the original Bech32 standard.

Feature	SegWit (Version 0)	Taproot (Version 1)
Address Prefix	bc1q	bc1p
Signature Type	ECDSA	Schnorr
Privacy	Low (Visible Logic)	High (Hidden Logic)
Encoding	Bech32	Bech32m

In the next section, we will analyze the ScriptPubKey Structure of P2TR.