arbo

arbo: tree in Esperanto.

MerkleTree implementation in Go. Compatible with the circomlib implementation of the MerkleTree, following the specification from https://docs.iden3.io/publications/pdfs/Merkle-Tree.pdf and https://eprint.iacr.org/2018/955.

Allows to define which hash function to use. So for example, when working with zkSnarks the Poseidon hash function can be used, but when not, it can be used the Blake2b hash function, which has much faster computation time.

Usage

// create new database
database, err := db.NewBadgerDB(c.TempDir())

// create new Tree with maxLevels=100 and Blake2b hash function
tree, err := arbo.NewTree(database, 100, arbo.HashFunctionBlake2b)


key := []byte("hello")
value := []byte("world")
err = tree.Add(key, value)


// There are cases where multiple key-values (leafs) are going to be added to a
// Tree, for these cases is more effitient to use:
invalids, err := tree.AddBatch(keys, values)

// generate the merkle proof of a leaf by it's key
value, siblings, err := tree.GenProof(key)

// verify the proof
verified, err := arbo.CheckProof(tree.hashFunction, key, value, tree.Root(), siblings)
if !verified {
	fmt.Println("proof could not be verified")
}

// get the value of a leaf assigned to a key
gettedKey, gettedValue, err := tree.Get(key)

// update the value of a leaf assigned to a key
err = tree.Update(key, value)

// dump the tree (the leafs)
dump, err := tree.Dump(nil) // instead of nil, a root to start from can be used

// import the dump into a tree
err = tree.ImportDump(dump)

// print graphviz diagram of the tree
err = tree.PrintGraphviz(nil) // instead of nil, a root to start from can be used

Usage with SNARKs compatibility

Arbo is designed to be compatible with circom merkle tree's snark-friendly merkletree. The only change needed is the hash function used for the Tree, for example using the Poseidon hash function:

tree, err := arbo.NewTree(database, 100, arbo.HashFunctionPoseidon)

Be aware of the characteristics of this kind of hashes, such as using values inside the finite field used by the hash, and also the computation time.

The interface of arbo uses byte arrays, and for the case of these kind of hashes (that usually work directly with finite field elements), arbo expects those values to be represented by little-endian byte arrays. There is a helper method to convert a *big.Int to []byte using little-endian:

bLen := tree.HashFunction().Len()
kBigInt := big.NewInt(100)

// convert *big.Int to byte array
kBytes := arbo.BigIntToBytes(bLen, kBigInt)

// convert byte array to *big.Int
kBigInt2 := arbo.BytesToBigInt(kBytes)