1# miksi [![Test](https://github.com/miksi-labs/miksi-core/workflows/Test/badge.svg)](https://github.com/miksi-labs/miksi-core/actions?query=workflow%3ATest)
 2
 3*From Esperanto, **miksi** (miks·i): to mingle, to blend, to mix, to shuffle*
 4
 5Ethereum mixer where all the computation & constructions are done offchain and then proved inside a zkSNARK to the smart-contract (both to *deposit* and *withdraw*).
 6
 7The client builds a MerkleTree, carries out the required computation, and then generates a zk-proof proving that the offchain computation has been done correctly (no leaf deletion, and only one correctly formatted leaf addition).
 8This approach requires only `~325.000 gas` to *deposit* (compared to `~1M gas` for an onchain computation approach) , and `~308.000 gas` to *withdraw*.
 9
10These gas savings come from the fact that we don't need to carry out the MerkleTree computations onchain. Instead, we prove the correctness of these offchain computations inside the snark proof, and verify this proof onchain. It's much cheaper to verify the proof than to carry out the necessary computations onchain.
11
12![](miksi-logo00-small.png)
13
14**Warning:** This repository is in a very early stage. The current version works, but is not finished. There are some improvements in the works.
15
16The WebApp to use miksi-core can be found at https://github.com/arnaucube/miksi-app
17
18## Circuits tests
19```
20npm run test-circuits
21```
22
23## Smart Contracts tests
24```
25npm run test-sc
26```
27
28### Compile circom circuit & generate Groth16 verifier contract
29
30```
31./compile-circuits.sh
32```
33
34
35## Spec draft
36**Note:** Both the spec and the code are works in progress. There are some pending improvements in the works, and some diagrams are needed to better explain things.
37
38### Deposit
39*All computations and constructions are done offchain and then proved inside a zkSNARK to the smart-contract*
40
41From the depositer's perspective, the interface facilitates the following flow:
42
431. Generate a random `secret` & `nullifier`
44
452. Compute the `commitment`, which is the Poseidon hash: `commitment = H(coinCode, amount, secret, nullifier)`, where:
46	- `coinCode`: code that specifies which currency is being used (`0`==ETH)
47	- `amount`: the amount to be deposited
48	- `secret`: random, private
49	- `nullifier`: random
50	
513. Fetch all the commitments from the smart-contract
52
534. Build the MerkleTree with the fetched commitments
54
555. Add the newly computed `commitment` to the MerkleTree
56
576. Generate a zkSNARK proof, which proves:
58	- you know the `secret` & `nullifier` for the `commitment` contained in the leaf you've just added to the MerkleTree
59	- the transition from `RootOld` (the current one in the Smart Contract) to `RootNew` has been done following the rules (no leaf deletion, and only one correctly formatted leaf addition, etc.)
60	
617. Send ETH to the smart-contract `deposit` call, together with the zkProof data
62
63Once these steps have been carried out, the smart-contract verifies the zkProof of the deposit, and if everything checks out ok, stores the commitment and the new root.
64
65The deposit circuit can be found [here](https://github.com/miksi-labs/miksi-core/blob/master/circuits/deposit.circom).
66
67### Withdraw
68*As before, all computations and constructions are done offchain and then proved inside a zkSNARK to the Smart Contract*
69
70From the withdrawer's perspective, the interface facilitates the following flow:
71
721. Fetch all the commitments from the smart-contract
73
742. Build the MerkleTree with the fetched commitments
75
763. Generate the siblings (merkle proof) for the `commitment` whose `secret` & `nullifier` you know
77
784. Generate a zkSNARK proof, which proves:
79        - you know a `secret` for a `nullifier` you reveal, whose `commitment` is in a MerkleTree with `root` matching the one stored in the smart-contract
80	
81If the zkProof verification passes, and the nullifier has not already been used, the smart-contract sends the ETH to the specified address.
82
83The withdraw circuit can be found [here](https://github.com/miksi-labs/miksi-core/blob/master/circuits/withdraw.circom).
84
85
86# Thanks
87Miksi is made possible thanks to [circom](https://github.com/iden3/circom), [circomlib](https://github.com/iden3/circomlib), [wasmsnark](https://github.com/iden3/wasmsnark), and the ideas developed in the [Zexe paper](https://eprint.iacr.org/2018/962.pdf).