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Describe adding a new leaf to the merkle tree.

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Justin Martin 2021-10-10 16:20:56 -07:00
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@ -77,4 +77,17 @@ forged "commitment" which has a colliding path within the merkle tree.
### Inserting a Commitment
When you insert a commitment into the Tornado contract's merkle tree, you are adding a new leaf node whose label is the
MiMC hash of your Pedersen commitment, and then traversing up the tree updating each subsequent parent node with a new
label based on the label updates that your new leaf introduces below.
Once your deposit has updated the tree, the label of the top-most node becomes the tree's new "root", and is added to
a rolling history containing the labels of the last 100 roots, for later use in processing withdrawal transactions.
The Tornado.cash deposit contracts are deployed with 20 "levels", with each level increasing the number of potential
leaves by a power of 2. That means that the contract's merkle tree supports up to 2^20 leaves, allowing for up to
1,048,576 deposits to be made into the contract before it needs to be replaced.
The reason behind this seemingly-low number of levels is that every deposit has to perform as many updates to the tree
as there are levels. A tree with more levels would require more gas per deposit, as well as correspondingly larger
proof sizes when withdrawing notes.