Merkleized Abstract Syntax Tree (MAST) is a technique used to improve the efficiency and flexibility of Bitcoin’s scripting language. MAST allows for more complex smart contracts by breaking them down into smaller parts, which can be selectively activated by certain conditions.
This means that only the parts of a smart contract that are needed for a particular transaction are executed, making transactions smaller, faster, and more efficient. To understand MAST, it’s important to understand the basics of Bitcoin’s scripting language.
Bitcoin transactions consist of inputs and outputs, and each input has a script attached to it. This script contains instructions that specify the conditions that must be met for the transaction to be valid. These conditions can be simple, such as requiring a particular digital signature, or they can be more complex, such as requiring multiple signatures or the fulfillment of a particular condition.
MAST allows these complex conditions to be broken down into smaller parts, which are stored in a Merkle tree. Each leaf node of the Merkle tree contains a small script fragment, and each non-leaf node contains a hash of its child nodes. The root of the Merkle tree is included in the transaction, along with a Merkle proof that allows a node to prove the presence of a specific script fragment in the tree.
When a transaction is executed, the relevant script fragments are activated, based on the conditions specified in the input script. This means that only the parts of the smart contract that are necessary for a particular transaction are executed, making transactions smaller, faster, and more efficient.