## Description of the Synchronization Task

- Note decryption
- Commitment Tree Witnesses

When you spend you need to create a spending Proof Spending proof includes statement that there is a note commitment for which you have the plain data. That note commitment was published before and is an output of a previous transaction.

Nodes track all the outputs and their commitments. But you have to prove that your secret note commitment (you don't want to reveal which one) is one of them.

The classic method for proving that your item is part of a list is to use a Merkle Proof. We'll explain what it is later.

Here the twist is that the Merkle Proof is secret. We know how to make it because we know the details of the note we spend. But we don't want to reveal it otherwise everyone will know it too. Therefore the Merkle Proof is a hidden parameter to the ZK circuit.

However, we still need to be able to calculate the MP for any of our unspent note, at any block height.

How we do that is the top of this section.