Merkelized Abstract Syntax Trees (MAST) is an improvement to the bitcoin protocol that will allow for more complex unlocking scripts on the bitcoin blockchain. Taproot is one codename for an upgrade that would add MAST.
While these scripts are available now, there are several drawbacks in the current system that prevent us from using them. First, they add additional size to a transaction, thereby raising the transaction cost. Secondly, using them would compromise user privacy by adding a distinctive format to Casa user transactions on the blockchain that would stand out.
MAST would make complex unlocking scripts look identical and have identical size to simpler ones. This would allow us to add new layers of security for our users. For example, we could offer a 3-of-5 wallet that reverts to a single signature wallet after a few years have passed without spending from it. This would add a failsafe in inheritance scenarios where a user dies unexpectedly and some of their keys are unrecoverable. The single signature fallback could be controlled by the user’s estate executor.