ecdh key exchange ; aes-256-gcm

Aes256Gcm.java

import org.bitcoinj.core.Utils;

import javax.crypto.Cipher;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.SecureRandom;
import java.util.Base64;

/**
 * @Author:yong.huang
 * @Date:2020-07-16 18:13
 */
public class Aes256Gcm {

    public static final int GCM_IV_LENGTH = 12;
    public static final int GCM_TAG_LENGTH = 16;

    public static byte[] encryptAES256GCM(byte[] plaintext, byte[] secret, byte[] nonce) throws Exception {
        // Get Cipher Instance
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        // Create SecretKeySpec
        SecretKeySpec keySpec = new SecretKeySpec(secret, "AES");
        // Create GCMParameterSpec
        GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, nonce);
        // Initialize Cipher for ENCRYPT_MODE
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmParameterSpec);
        // Perform Encryption
        return cipher.doFinal(plaintext);
    }

    public static String decryptAES256GCM(byte[] cipherText, byte[] secret, byte[] nonce) throws Exception {
        // Get Cipher Instance
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        // Create SecretKeySpec
        SecretKeySpec keySpec = new SecretKeySpec(secret, "AES");
        // Create GCMParameterSpec
        GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, nonce);
        // Initialize Cipher for DECRYPT_MODE
        cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmParameterSpec);
        // Perform Decryption
        byte[] decryptedText = cipher.doFinal(cipherText);
        return new String(decryptedText);
    }

    public static void main(String[] args) throws Exception {
        byte[] secret = Utils.HEX.decode("88daf6993cd89eb2f95da19c961962ed1ed017edb44816e778497538e06e86fb");
        int GCM_IV_LENGTH = 12;

        byte[] nonce = new byte[GCM_IV_LENGTH];
        SecureRandom random = new SecureRandom();
        random.nextBytes(nonce);

        String plainText = "{\"jsonrpc\":\"2.0\",\"method\":\"open_wallet\",\"id\":1,\"params\":{\"name\":null,\"password\":\"\"}}";
        System.out.println("Original Text : " + plainText);
        byte[] cipherText = Aes256Gcm.encryptAES256GCM(plainText.getBytes(), secret, nonce);
        System.out.println("Encrypted Text : " + Base64.getEncoder().encodeToString(cipherText));
        String decryptedText = Aes256Gcm.decryptAES256GCM(cipherText, secret, nonce);
        System.out.println("Decrypted Text : " + decryptedText);
    }
}

EcdhKeyExchange.java

import org.apache.commons.codec.binary.Hex;
import org.bitcoinj.core.ECKey;
import org.bitcoinj.core.Utils;
import org.bouncycastle.jce.ECNamedCurveTable;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.jce.spec.ECParameterSpec;
import org.bouncycastle.jce.spec.ECPrivateKeySpec;
import org.bouncycastle.jce.spec.ECPublicKeySpec;

import javax.crypto.KeyAgreement;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Security;

/**
 * @Author:yong.huang
 * @Date:2020-07-16 18:12
 */
public class EcdhKeyExchange {

    public static byte[] computeSecret(byte[] priv, byte[] otherPub) throws Exception {
        KeyAgreement ka = KeyAgreement.getInstance("ECDH", "BC");
        PrivateKey privateKey = loadPrivateKey(priv);
        PublicKey publicKey = loadPublicKey(otherPub);
        ka.init(privateKey);
        ka.doPhase(publicKey, true);
        byte[] secret = ka.generateSecret();
        return secret;
    }

    private static PrivateKey loadPrivateKey(byte[] priv) throws Exception {
        ECParameterSpec params = ECNamedCurveTable.getParameterSpec("secp256k1");
        ECPrivateKeySpec keySpec = new ECPrivateKeySpec(new BigInteger(priv), params);
        KeyFactory kf = KeyFactory.getInstance("ECDH", "BC");
        return kf.generatePrivate(keySpec);
    }

    private static PublicKey loadPublicKey(byte[] pub) throws Exception {
        ECParameterSpec params = ECNamedCurveTable.getParameterSpec("secp256k1");
        ECPublicKeySpec pubKey = new ECPublicKeySpec(params.getCurve().decodePoint(pub), params);
        KeyFactory kf = KeyFactory.getInstance("ECDH", "BC");
        return kf.generatePublic(pubKey);
    }

    public static void main(String[] args) throws Exception {
        Security.addProvider(new BouncyCastleProvider());
        String priv = "465568154bbf7448f2678cd4ef08fa0ae8e57a6a978e032386860f34e86f9507";
        ECKey ecKey = ECKey.fromPrivate(new BigInteger(priv, 16));
        byte[] privKeyBytes = ecKey.getPrivKeyBytes();
        String otherPub = "03a9120b42a6d8d4051af874c230841e5794367bb8792c55bcb1ce2e379cc9a826";
        byte[] secret = EcdhKeyExchange.computeSecret(privKeyBytes, Utils.HEX.decode(otherPub));
        System.out.println("secret:" + Hex.encodeHexString(secret));
    }
}