Anonymous transactions engine for Waves blockchain

This is anonymous transaction engine, implemented for waves blockchain. This is prototype, so, the project is very experimental.

Dependencies

nodejs@11.15.0

Waves node

The implementation works with modified waves node, supporting groth16verify function. The source code is at https://github.com/snjax/Waves/tree/feature/groth16verifier.

Current state of .env file is

WAVES_RPC=http://dev-node-aws-fr-2.wavesnodes.com:6869/
WAVES_CHAINID=D
DAPP=2rdJzzFcVeignvBhKyubsPjxM8WdEYyje573eaebEDM8
MNEMONIC=<your seed passphrase>

The dApp is deployed at address 3FQ19SGXg2gXcd1AvQAwaP6Sd35knEqggVm at the moment.

Faucet

Type node faucet.js to get 100 test WAVES for your address, corresponding to MNEMONIC.

Cryptography

Anonymity is zkSNARK-driven, we use circom and groth16 proving scheme at BN254. You may read more about the circuit at circuit.md.

The client use Curve25519 to sign ordinary waves transactions and BabyJubJub to prove ownership of the assets inside the zkSNARK. For hashing we use Pedersen hash anywhere.

At current version anonimity set is not merkelized. Pedersen based merkle proofs use too much constraints for current circom version. We consider to use no MiMC hashes here. For futher versions of circom or for circuits implemented with bellman anonymity set may be expanded by several orders of magnitude.

We use utxo model for this solution. All utxo data is encrypted via receiver's public key on BabyJubJub curve.

Functionality

Deposits

Deposits are signed by user's private key at Curve25519. Each deposited asset corresponds to utxo inside the dApp. The user can deposit the asset to any public key at BabyJubJub. So, the asset may be received instantly by another user without any additional transfers. The nullifier is computed from users's private key and salt, so, the sender can create the utxo, but, if he do not know the receiver's private key, he cannot compute the nullifier and track, when the asset is spent.

Transfers

We use 2to2 transfers. The transactions are not signed via any keys, we use custom transaction verifier here. The fee is payable inside the zkSNARK. Input utxos are mixed with the set of random utxos.

To get information about received utxos the user scans all messages and tries to decrypt them. If the message is decrypted successfully, the user can manage utxo, corresponding to this message.

Withdrawals

The transactions are not signed, the fee is payable inside the snark. The receiver address is specified inside the public input of the snark. Input utxo is mixed with the set of random utxos.

Deploy

The first clone this repository via

git clone https://github.com/wavesplatform/anonymous-transactions-prototype

After that install all npm packages

cd anonymous-transactions-prototype && npm i&& cd zksnark && npm i && cd .. && cd zcrypto && npm i && cd ..

Provide trusted setup of circuits

cd zksnark && npm run compile && npm run setup && cd ..

Specify .env file and deploy the contract to the blockchain

WAVES_RPC	url of waves node
WAVES_CHAINID	chain id letter
MNEMONIC	seed passphrase
DAPP	dapp public key

node deploy.js

Specify DAPP property at .env file.

Client usage

Install all dependencies

npm i&& cd zksnark && npm i && cd .. && cd zcrypto && npm i && cd ..

.env file must be composite of following variables

WAVES_RPC	url of waves node
WAVES_CHAINID	chain id letter
MNEMONIC	seed passphrase
DAPP	dapp public key

Now MNEMONIC is the seed of current user account and DAPP is dApp account public key, obtained from MNEMONIC at Deploy stage. You may setup several client enviroments for different MNEMONIC and play with client using following commands:

nodejs cli.js <command> <options>
account details command
=============
    nodejs cli.js details <option>
    Print details of current seed (pubkey and address at waves, pubkey and
    private key at the DApp)
    Print anonymous and not anonymous balance
    -s or --seed <seed>

deposit command
=========================
    nodejs cli.js deposit <options>
    Deposit waves to the DApp.
    -s or --seed <seed>
      or
    --pub <pubkey>

    -b or --balance <balance>

withdrawal command
========================
    nodejs cli.js withdrawal <options>
    Withdraw waves to address
    -s or --seed <seed>
      or
    -a or --address <address>

    -b or --balance <balance>

transfer command
==============
    nodejs cli.js transfer <options>
    Transfer waves to another address.
    -s or --seed <seed>
     or
    --pub <pubkey>

    -b or --balance <balance>


Options:
  --version   Show version number                                      [boolean]
  -h, --help  Show help                                                [boolean]

TODO

• Multiparty trusted setup
• More powerful engines (further versions of circom or current version of bellman) for circuit and anonimity set merkelization (we are still not going to use MiMC here)
• Coinselect library for more optimized operations with assets