How can i generate private key and address using web3j instead of creating keystore json file

  • it is a good question – Nulik Feb 27 '18 at 15:10

Below is my approach, verified by importing the result privatekey into MetaMask and get the same address as expected.

private static JSONObject process(String seed){

         JSONObject processJson = new JSONObject();

         try {
            ECKeyPair ecKeyPair = Keys.createEcKeyPair();
            BigInteger privateKeyInDec = ecKeyPair.getPrivateKey();

            String sPrivatekeyInHex = privateKeyInDec.toString(16);

            WalletFile aWallet = Wallet.createLight(seed, ecKeyPair);
            String sAddress = aWallet.getAddress();

            processJson.put("address", "0x" + sAddress);
            processJson.put("privatekey", sPrivatekeyInHex);

        } catch (CipherException e) {
        } catch (InvalidAlgorithmParameterException e) {
        } catch (NoSuchAlgorithmException e) {
        } catch (NoSuchProviderException e) {

        return processJson;

main(){  // unit test 
    String seed = UUID.randomUUID().toString();
    JSONObject result = process(seed); // get a json containing private key and address
  • String sPrivatekeyInHex = privateKeyInDec.toString(16); What this line does ? Could you explian ? – Ajit Soman Feb 28 '18 at 5:12
  • 1
    @Ajit Soman getPrivateKey() is returning decimal, usually we need to use hex string private key. – pyang Feb 28 '18 at 5:42
  • I have posted a question . could you provide me some information regarding this: ethereum.stackexchange.com/questions/41194/… – Ajit Soman Feb 28 '18 at 7:54

This is what I did:

public class MainActivity extends AppCompatActivity {
    private WalletFile wallet;
    private String password = "PASSWORD";
    protected void onCreate(Bundle savedInstanceState) {


        try {
            wallet = createWallet();
        } catch (Exception e) {
            System.out.println("BIG RIP");

    public WalletFile createWallet() throws Exception {
        ECKeyPair keyPair = Keys.createEcKeyPair();
        return Wallet.createLight(password, keyPair);


    private void setupBouncyCastle() {
        final Provider provider = Security.getProvider(BouncyCastleProvider.PROVIDER_NAME);
        if (provider == null) {
            // Web3j will set up the provider lazily when it's first used.
        if (provider.getClass().equals(BouncyCastleProvider.class)) {
            // BC with same package name, shouldn't happen in real life.
        // Android registers its own BC provider. As it might be outdated and might not include
        // all needed ciphers, we substitute it with a known BC bundled in the app.
        // Android's BC has its package rewritten to "com.android.org.bouncycastle" and because
        // of that it's possible to have another BC implementation loaded in VM.
        Security.insertProviderAt(new BouncyCastleProvider(), 1);

For some reason, in newer versions of web3j, Keys.createEcKeyPair() throws an error, so I copied some code from here: https://github.com/serso/web3a/blob/4dda74db948f8cbd9a79ba4b9ab456316ea52c4d/app/src/main/java/org/solovyev/android/web3a/App.java#L47 to set up bouncy castle before running.

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