MAST would allow larger intelligent contracts and increase privacy in blockchain

The Merkelized Abstract Syntax Trees (MAST) are an improvement proposal for Bitcoin and other cryptocurrencies that use SegWit, such as Litecoin. Its adoption would allow greater privacy, smaller transaction sizes and smaller intelligent contracts, by using a combination of  Pay To Script Hash  (P2SH), Abstract Syntax Trees (ASTs) and the tree-like data structure called Merkle Tree .

MAST is in Github as a Bitcoin Improvement Proposal or BIP, still without number and uploaded for the first time on April 2, 2016. The modality was devised by the developers Russell O'Connor, Pieter Wuille and Peter Todd , although it has been expanded or rethought by various developers, including  Johnson Lau, Mark Friedenbach, Gregory Maxwell and  MIT scholars . But, how could MASTs improve the network in such a way?

Let's suppose that Carlos has a certain amount of bitcoin , but, foreseeing that something may happen to him, chooses that if he spends six months without spending them, he would like his sister Andrea to have access to them without giving him his private keys. In the same way, Andrea would like to be able to leave her bitcoin to her husband Jesus, in case she has two months without spending it, and so a long network of infinite scripts could be made where people use conditionals to distribute their funds, which takes up a lot space.

It could also be the case that Carlos does not want his sister or brother-in-law to know what would happen to the funds if he is unable to move them, or that a company is running a confidential business from which they would not reveal all these possible transactions. . At the moment, the Bitcoin network would have all these data public, even if they were options where the funds would go to another person only when another event happens.

MAST could offer a solution to these problems. Firstly, through the Merkle Tree function, already present in the chain of blocks or blockchain,  the information blocks in pairs and generates a hash for each block of data. Then, the generated hashes are again grouped in pairs and generate a new hash that in turn is grouped with another and  repeated way up the tree until reaching a single block, the root of the tree, which is called root hash pointer (root hash) and registers in the address of the current block (block hash) in order to reduce the space occupied by each block. This structure of hash pointers allows to cross any point of the tree to  verify that the data has not been manipulated, since, as with the chain of blocks, if someone manipulates some block of data in the lower part of the tree, it will cause the pointer hash that is one level higher does not match

In MAST, the Merkle Tree would be integrated with the Abstract Syntax Trees (ASTs) function, which is a way to describe a program by dividing it into individual parts to make it easier to analyze and optimize. These parts would be verified by the Merkle Tree function without the need to present the chain as a whole whenever verification is required.

To these two functions, in the BIP proposed by Johnson Lauthe P2SH is added. Normally Bitcoin are transferred from one address to another using an output information in the form of a script. The script is a code that blocks and releases the Bitcoin again and again to perform the movements. When using Pay to Script Hash (P2SH), this script is not enough to change the site backgrounds, but it is encrypted so that it looks like a random series of characters that can not be deciphered as the original code, and can only be identified as a specific transaction with the "hash" included in the initial output information. In simpler words, the nodes can not identify the exit script of an exact address, but they can verify that the encrypted exit code of the transaction is the same, see if it meets the requirements, and then confirm it.

Combining these Merkle Trees, Abstract Syntax Tree and P2SH tools to form MASTs increases the security of transactions and reduces the amount of data used, which would not only minimize the amount of information in transactions, but it would also allow larger intelligent contracts due to the compression of the data.

This adoption could be very simple and be a soft fork to have a majority approval. Some people believe that the increasing use of atomic swaps  that allow direct changes between cryptocurrencies  makes transactions too easy to track by remaining permanently in the blockchain. The use of MAST could help make operations more private because those operations scheduled but not performed immediately are hidden. However, its adoption by the entire Bitcoin network could take a long time, as it has in the case of  SegWit.. However, it would be very beneficial for companies that want to keep their scheduled transactions hidden or to automate testaments in cases of accidental deaths.