Bitcoin users may, before long, be able to benefit from a trick called “Taproot.” First proposed[1] by Bitcoin Core contributor and former Blockstream CTO Gregory Maxwell, Taproot would expand on Bitcoin’s smart contract flexibility, while offering more privacy in doing so. Even the most complex smart contracts would, on the blockchain, typically be indistinguishable from regular transactions.
While a big undertaking, this is not just theory. Several of the most prolific Bitcoin Core contributors — including Pieter Wuille, Anthony Towns, Johnson Lau, Jonas Nick, Andrew Poelstra, Tim Ruffing, Rusty Russell and, indeed, Gregory Maxwell — are working on a Schnorr signature[2] proposal that would include Taproot, all in one protocol upgrade.
Here’s what Taproot is and how it works.
MAST
All bitcoins are essentially “locked up” in scripts: a couple lines of code embedded in a transaction included in the blockchain, that define how the coins can be spent in the next transaction. Spending conditions usually involve providing a signature to prove ownership of the coins. But other, well-known conditions for example include timelocks (coins can only be spent after a specific block height or date) or multisig (coins can only be spent if some number of private keys out of a set of private keys provide signatures).
Different conditions can be mixed and matched, to create complex types of smart contracts. An example of such a contract could be that coins can be spent if both Alice and Bob sign, or if Alice alone signs after a week has passed, or if Bob alone signs while also providing a secret number. Whichever of these three conditions is met first, is how the coins are spent.
Since 2012, scripts (the conditions) are often not publicly visible at first; only the
