Ethernest

A multi-chain crypto wallet app for Android. You can hold ETH and tokens on many EVM networks, send and receive with QR codes, swap tokens on testnet, view your NFTs, and buy ETH with Indonesian payment methods through Midtrans.

Features

• Create or import a wallet, protected by a PIN (ready for fingerprint login)
• Many networks: Ethereum, Sepolia, BSC, Avalanche, Polygon, Arbitrum, Optimism, Base, Fantom, or any EVM network through a custom RPC
• Your assets: ETH, ERC-20 tokens, and NFTs (ERC-721 and ERC-1155), with real coin icons, candlestick price charts, and transaction history
• Send and receive ETH with QR codes, a set amount, address sharing, and "deposit from exchange"
• Swap tokens on-chain: MATS, IDRX, popular EVM tokens, and any extra token that has a pool
• Buy ETH inside the app: pay through Midtrans in an in-app page, with a live ETH/IDR price

Tech stack

• App: Java 11, Android SDK 36, Material Design 3, RecyclerView, ViewPager2, WebView
• Blockchain: Web3j 4.9 with Infura RPC
• Data: Retrofit + Gson (CoinGecko, Etherscan), Room
• Security: EncryptedSharedPreferences and the Android Keystore
• Contracts and buy server: Solidity, Hardhat, Express.js, Midtrans

How the project is split

Folder	What it is
app/	The Android app
smart-contracts/contracts/	ERC-20 token and swap pool contracts
smart-contracts/scripts/	Deploy, mint, and liquidity scripts
smart-contracts/server/	The "buy ETH" backend (Express + Midtrans)

Set up the Android app

1. Open the project in Android Studio.

2. Create local.properties in the project root (see local.properties.example) and fill it in:

   INFURA_PROJECT_ID=xxx
   ETHERSCAN_API_KEY=xxx
   BSC_RPC_URL=https://bsc-dataseed.bnbchain.org
   AVALANCHE_RPC_URL=https://api.avax.network/ext/bc/C/rpc
   POLYGON_RPC_URL=https://polygon.drpc.org
   
   # Swap tokens and pools (from the contract deploy step below)
   MATS_TOKEN_ADDRESS=xxx
   MATS_SWAP_POOL_ADDRESS=xxx
   IDRX_TOKEN_ADDRESS=xxx
   IDRX_SWAP_POOL_ADDRESS=xxx
   # Optional presets: SWAP_USDT_*, SWAP_USDC_*, ...
   # Optional extra slots: SWAP_TOKEN_1_* to SWAP_TOKEN_12_*
   
   # Buy ETH backend
   BUY_BACKEND_BASE_URL=http://10.0.2.2:8787/
   MIDTRANS_PAYMENT_URL=

3. Sync Gradle and run the app.

Reaching the buy server from the app:

• The Android emulator reaches your computer at http://10.0.2.2:8787/.
• A real phone needs your computer's or server's IP, for example http://192.168.1.10:8787/.
• Over USB, you can also run adb reverse tcp:8787 tcp:8787.

Buy server (Midtrans)

The app never stores the treasury's private key. Buying ETH works like this:

1. The app creates an order on the backend.
2. The backend creates a Midtrans payment, which opens inside the app.
3. Once Midtrans confirms the payment, the backend sends ETH to your wallet.

The ETH/IDR price is calculated on the server in real time from CoinGecko, then Indodax, with Binance ETH/USDT plus the USD/IDR rate as a fallback.

cd smart-contracts
npm install
cp .env.example .env
npm run start:buy-server

Minimum .env for the buy server:

MIDTRANS_SERVER_KEY=xxx
MIDTRANS_IS_PRODUCTION=false
INFURA_PROJECT_ID=xxx
BUY_TREASURY_PRIVATE_KEY=testnet_treasury_key_without_0x
BUY_DEV_MODE=true

Endpoint	What it does
GET /health	Health check (try http://127.0.0.1:8787/health)
GET /api/price/eth-idr	Current ETH price in rupiah
POST /api/buy/eth	Create a buy order
POST /api/midtrans/notification	Midtrans payment webhook

For production, run the buy server on a server with HTTPS and set the Midtrans webhook to https://your-domain.com/api/midtrans/notification.

Smart contracts and swaps

The smart-contracts folder has an ERC-20 token and simple ETH/token swap pools for testnet.

How swaps work in the app:

• A token can be swapped once it has a token address, a pool address, and liquidity. By default that's MATS and IDRX.
• Popular tokens (USDT, USDC, DAI, WBTC, LINK, UNI, AAVE, SHIB, PEPE, ARB, OP) also appear in the picker.
• A token without a pool shows "Butuh pool" (needs a pool) and its swap button stays locked. Once the pool is set up it shows "Aktif" (active).

Fastest way: deploy everything on Sepolia

Get some Sepolia ETH from a faucet first, then:

cd smart-contracts
cp .env.example .env

INFURA_PROJECT_ID=xxx
DEPLOYER_PRIVATE_KEY=testnet_key_without_0x
TEST_SWAP_TOKENS=MATS,IDRX,USDT,USDC,DAI,WBTC,LINK,UNI,AAVE,SHIB,PEPE,ARB,OP
TEST_POOL_ETH_LIQUIDITY=0.005

npm install
npm run compile
npm run deploy:testnet-routes

The script deploys mock tokens, creates an ETH/token pool for each, adds liquidity, and prints the lines to paste into local.properties. Paste them, sync Gradle, and run the app.

Step by step: one token and one pool

INFURA_PROJECT_ID=xxx
DEPLOYER_PRIVATE_KEY=xxx_without_0x
TOKEN_NAME=Mats Token
TOKEN_SYMBOL=MATS
TOKEN_INITIAL_SUPPLY=1000000
POOL_TOKEN_SYMBOL=MATS
POOL_TOKEN_ADDRESS=your_token_address
POOL_SWAP_ADDRESS=your_pool_address

npm run compile
npm run deploy:token   # deploy the ERC-20 token
npm run deploy:pool    # deploy its swap pool
npm run seed:pool      # add liquidity

For another token, set POOL_TOKEN_SYMBOL and POOL_TOKEN_ADDRESS, run npm run deploy:pool, copy the printed SWAP_TOKEN_1_* lines into local.properties, then run npm run seed:pool.

Security

• Users' private keys are encrypted with the Android Keystore and EncryptedSharedPreferences.
• The buy server's treasury key lives only in the backend .env, never in the app.
• local.properties and smart-contracts/.env are ignored by Git, so secrets don't get pushed.

License

Released under the MIT License.