Taproot & Advanced Scripts

The Taproot upgrade, activated on November 14, 2021 (block 709,632), was the most significant improvement to Bitcoin's scripting capabilities since SegWit. Taproot fundamentally changes how Bitcoin scripts work — making complex transactions cheaper, more private, and more flexible.

The Problem Before Taproot

Before Taproot, complex Bitcoin scripts (like multisig or time-locked transactions) had several issues:

• Privacy: When you spent from a P2SH multisig address, the full script was revealed on-chain. Anyone could see it was a 2-of-3 multisig, exposing your security setup to the world.
• Cost: Complex scripts required more data on-chain, meaning higher transaction fees.
• Distinguishability: Different transaction types looked different on-chain — a simple payment looked different from a multisig spend, reducing fungibility.

How Taproot Works

Taproot combines three technologies:

1. Schnorr Signatures (BIP 340):

Taproot replaces ECDSA signatures with Schnorr signatures, which have a crucial property: linearity. This means multiple signatures can be mathematically combined into a single signature that is indistinguishable from a regular one-person signature. A 2-of-3 multisig transaction can now appear on-chain as a simple single-signature payment.

2. MAST (Merkelized Abstract Syntax Trees — BIP 341):

With MAST, you can create a script with many spending conditions, but only reveal the one you actually use. Imagine a script with three possible spending paths:

• Path A: Alice and Bob sign together (cooperative close).
• Path B: Alice alone after 30 days (timeout).
• Path C: Arbiter signs (dispute resolution).

If Alice and Bob cooperate (Path A), only Path A is revealed. Paths B and C remain completely hidden — no one even knows they existed. This is a massive privacy improvement.

3. Tapscript (BIP 342):

Tapscript updates Bitcoin's scripting language with new opcodes and rules optimized for the Taproot framework. It makes it easier to add new opcodes in the future through soft forks, ensuring Bitcoin's programmability can evolve over time.

Taproot Addresses: P2TR

Taproot introduced a new address format: Pay-to-Taproot (P2TR), which starts with bc1p. These addresses encode a single public key that can be spent in two ways:

• Key path spend: A simple signature (or aggregated Schnorr signature from multiple parties) — cheap and private.
• Script path spend: Falls back to a MAST tree of scripts if the key path isn't used.

Real-World Impact

Taproot's benefits are substantial for the entire ecosystem. Lightning Network channel opens and closes now look identical to regular transactions. Multisig wallets gain significant privacy. Complex contracts become cheaper. For Sri Lankan Bitcoin users, Taproot means that whether you are making a simple payment at a Colombo merchant or managing a sophisticated multisig treasury, your transactions look the same on-chain — enhancing financial privacy in an environment where economic surveillance is an increasing concern.