Overview

⚠️⚠️⚠️ Caution! This is beta / testnet technology ⚠️⚠️⚠️

WIP - TODO

• better documentation for contract to contract example
• document Rust contract for contract to contract example

Introduction

NEAR's MPC allows a NEAR Account to create derivative accounts (public keys) and signatures of transactions for other blockchains.

Several MPC nodes maintain a single public key. This key is combined with your NEAR AccountId (unique) and a chosen "path" offset (chosen by client). This produces a new and unique public key. The generation of signatures via the MPC nodes can only be authorized by same NEAR Account by calling the sign method of the MPC contract.

The creation of secp256k1 public keys for Bitcoin and EVM chains is currently supported.

Flow (how it works)

1. Obtain the MPC public key (near view [MPC_CONTRACT_ID] public_key) and hardcode into .env or code
2. Choose a path for the derived account (public key) see: Path naming conventions
3. Use ./src/kdf.ts -> generateAddress to generate the derived account address and public key
4. Use the sign method of ./src/near.ts -> sign which calls the MPC contract to sign payload (hash of TX)
5. Using a library (ethers/bitcoinjs-lib) combine the transaction and signature to create signed transaction
6. Broadcast the transaction e.g. sendRawTransaction

Installation

yarn

CREATE .env FILE in root of project

NEAR_ACCOUNT_ID="[NEAR_TESTNET_ACCOUNT]"
NEAR_PRIVATE_KEY="[NEAR_ACCOUNT_PRIVATE_KEY]"
MPC_PATH="[MPC_PATH]"
MPC_CHAIN="[ethereum|bitcoin]"
MPC_CONTRACT_ID="multichain-testnet-2.testnet"
MPC_PUBLIC_KEY="secp256k1:4HFcTSodRLVCGNVcGc4Mf2fwBBBxv9jxkGdiW2S2CA1y6UpVVRWKj6RX7d7TDt65k2Bj3w9FU4BGtt43ZvuhCnNt"

For dogecoin testnet (link below)

TATUM_API_KEY=""

For MPC_PATH please refer to:

Path naming conventions

How to Use Commands

(as a user or dev to verify everything works)

1. Read the Installation steps and set up all environment variables first with .env file.
2. Use the commands to generate addresses first.
3. Fund these addresses with the Testnet Faucets provided in the links below.
4. Use the commands to send funds from your generated addresses.

Prebuilt Commands

yarn start [commands]

Command List

• -ea - ethereum addressm (EVM)
• -ba - bitcoin testnet address
• -da - dogecoin testnet address
• -ra - ripple testnet address
• -s - sign sample payload using NEAR account
• -etx - send ETH
• -btx - send BTC
• -dtx - send DOGE (requires API KEY)
• -rtx - send XRP

Sending Options

• --amount - amount to send (ETH or sats)
• --to - destination address

EVM Contract Deployment and Interactions (advanced)

Usage: yarn start [commands]

Command List

• -d, -edc - deploy contract
• --to - the contract address to view/call
• -v, -view - view contract state (readonly call)
• -c, -call - call contract method
• --path - path to EVM bytecode file from root of this project
• --method - name of method view/call
• --args - arguments e.g. '{"address":"0x525521d79134822a342d330bd91da67976569af1"}' in single quotes
• --ret - list of return parameter types (if any) e.g. ['uint256']

NFT Example

After setting up all your environment variables and ensuring your calling EVM address has ETH for gas.

Start by deploying a new NFT contract:

1. yarn start -d

Check explorer link and make sure contract is deployed successfully.

Take contract address from console result and call:

2. yarn start -c --to 0x[CONTRACT ADDRESS FROM STEP 1]

This will mint a token to default address 0x525521d79134822a342d330bd91da67976569af1.

View the balanance of the default address using:

3. yarn start -v --to 0x[CONTRACT ADDRESS FROM STEP 1]

Which should output 1 the NFT balance of default address 0x525521d79134822a342d330bd91da67976569af1

Proxy call MPC sign from NEAR Contract (advanced)

To deploy the NEAR contract use cargo-near.

Install cargo-near and near-cli

• cargo-near - NEAR smart contract development toolkit for Rust
• near CLI-rs - Iteract with NEAR blockchain from command line

cargo build

cargo near create-dev-account

cargo near deploy [ACCOUNT_ID]

The NEAR contract has the following features:

1. sign method accepts a payload that is the unhashed RLP encoded EVM transaction data e.g. 6a627842000000000000000000000000525521d79134822a342d330bd91DA67976569aF1 calls the method mint with an address argument of 525521d79134822a342d330bd91DA67976569aF1
2. PUBLIC_RLP_ENCODED_METHOD_NAMES stores public EVM method name hashes that can be called from this NEAR contract to the destination address e.g. the method name mint hashes 6a627842000000000000000000000000
3. COST must be paid in NEAR
4. path and key_version arguments are passed through to MPC sign call, but in the future could be used as additional features for applications or security

To use, set the following .env vars accordingly:

NEAR_PROXY_ACCOUNT="true"
NEAR_PROXY_CONTRACT="true"
NEAR_PROXY_ACCOUNT_ID="futuristic-anger.testnet"
NEAR_PROXY_PRIVATE_KEY="ed25519:..."

With NEAR_PROXY_CONTRACT="true" the script will call sign method of the proxy contract you deployed using cargo near deploy.

To verify, send some ETH using yarn start -etx.

With NEAR_PROXY_ACCOUNT="false" you will not be able to send ETH using the sign method of the proxy contract. Why? Because this would mean any NEAR account can send ETH from the derived account of the proxy contract. Oh no! The proxy contract protects against arbitrary transactions using this check:

let owner = env::predecessor_account_id() == env::current_account_id();

// check if rlp encoded eth transaction is calling a public method name
let mut public = false;
for n in PUBLIC_RLP_ENCODED_METHOD_NAMES {
	if rlp_payload.find(n).is_some() {
		public = true
	}
}

// only the NEAR contract owner can call sign of arbitrary payloads for chain signature accounts based on env::current_account_id()
if !public {
	require!(
		owner,
		"only contract owner can sign arbitrary EVM transactions"
	);
}

Enjoy!

References & Useful Links

Examples

Live Example - NEAR Testnet, Sepolia, Bitcoin Testnet

A frontend example you can run locally

Docs

Path naming conventions

Chain Signatures Docs

Chain Signatures Use Cases

MPC Repositories

MPC Repo

Faucets and API Keys

Sepolia Faucet

Bitcoin Testnet Faucet

For Dogecoin, you will need to register for Tatum API (free plan):

Dogecoin Tatum API and docs

Dogecoin Testnet Faucet

XRP Ledger

XRP Ledger Testnet Faucet

XRP Ledger Testnet Explorer