offchainer

Tools to have ethereum develop smart contract interacting with off-chain data and computation. Aims at facilitating development of smart contract in scenarios where some data and associated computation needs to be off-chain, either for privacy or efficiency reasons. We take computations out of the smart contract, while ensuring correctness, using commitments and zk-proofs.

Reference Paper

Smart contract with secret parameters Marin Thiercelin, Chen-Mou Cheng, Atsuko Miyaji, Serge Vaudenay SCIS 2020

Dependencies

Library dependencies:

• nodejs v12 or above
• solc v 0.5.13 to 0.5.16 (Bug with versions 0.6.1)
• zokrates

Nb: Current Zokrates version doesn't work with latest solc version (0.6.1), you should downgrade solc to 0.5.*

Test network dependencies:

• geth

Use the library:

Development

In your project workspace:

• run npm install git+https://github.com/marinthiercelin/offchainer.git
• run nodejs offchainer init <project_name>
• write your onchain code in ./src/<project_name>_onchain.sol
• write your offchain code in ./src/<project_name>_offchain.zok.

Ethereum network

You need to have a running ethereum node on your machine. We've provided a script to generate a test private network with 3 accounts with some ether:

• "2db685e56b28f87e60fdd62eee66d8b7c5a9ba8e"
• "3fa68075aa987cf3b61ed52b54c936ab2007f38b"
• "f593c5e1899a255ded9a7bb90355cfd12a82bda3"

They can be unlocked with password : 'the_password'.

To start the test network, run:

• cd ./nodes_modules/offchainer/test_network
• ./start.sh

Configuration

You can configure the project by modifying ./src/config.json

Execution

Generate the SNARKS keys:

run nodejs offchainer generate

or use as a nodejs module:

const offchainer = require('offchainer');
const config = require('./config.json');
offchainer.generate(config);

The owner can deploy the contracts with:

nodejs node_modules/offchainer deploy <account> <password> <value> <secret> <arg1> <arg2> etc.

or use as a nodejs module:

offchainer.deploy(config, account, password, value, secret, arg1, arg2);

This will generate 2 files in the folder instances a public file that can be shared with the users, and a key file that needs to stay private.

The owner can start listening for private computations requests with:

nodejs node_modules/offchainer listen <account> <password> <instance_pub> <instance_key>

or use as a nodejs module:

offchainer.listen(config, account, password, instance_pub, instance_key);

The user can interact with the contract using:

nodejs node_modules/offchainer call <account> <password> <instance_pub> <method_name> <value> <arg1> <arg2> etc.

or use as a nodejs module:

offchainer.call(config, account, password, instance_pub, method_name, value, arg1, arg2);