Android AES Encryption and Decryption

1. EncryptUtil

import android.util.Base64;

import java.security.InvalidParameterException;
import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

/**
 * AES encryption and decryption
 * 

 * 1. key's length >= 16
 * 2. iv's length > 16
 * 3. "transformation": AES/CBC/PKCS5Padding
 * 4. iv=12(bytes) length=128(bits)
 * 5. iv=24(bytes) length=192(bits)
 * 6. iv=32(bytes) length=256(bits)
 * 

 * Created by Anter on 2018/4/11.
 */

public class EncryptUtil {

    private EncryptUtil() {
    }

    /**
     * Base64 decode then AES decrypt
     *
     * @param data           Data to decrypt
     * @param key            Decrypt key
     * @param iv             Decrypt key
     * @param transformation AES/CBC/PKCS5Padding
     * @return Decrypted bytes
     * @throws Exception Decrypt exception
     */
    public static byte[] decryptBase64EncodeData(byte[] data, byte[] key, byte[] iv, String transformation) throws Exception {

        if (data == null || data.length == 0
                || key == null || key.length < 16
                || iv == null || iv.length < 16
                || transformation == null || transformation.length() == 0) {
            throw (new InvalidParameterException());
        }

        byte[] textBytes = Base64.decode(data, Base64.DEFAULT);
        AlgorithmParameterSpec ivSpec = new IvParameterSpec(iv);
        SecretKeySpec newKey = new SecretKeySpec(key, "AES");
        Cipher cipher = Cipher.getInstance(transformation);
        cipher.init(Cipher.DECRYPT_MODE, newKey, ivSpec);
        return cipher.doFinal(textBytes);
    }

    /**
     * AES encrypt then base64 decode
     *
     * @param data           Data to encrypt
     * @param key            Encrypt key
     * @param iv             Encrypt key
     * @param transformation AES/CBC/PKCS5Padding
     * @return Encrypted bytes
     * @throws Exception Encrypt exception
     */
    public static byte[] encryptAndBase64Encode(byte[] data, byte[] key, byte[] iv, String transformation) throws Exception {

        if (data == null || data.length == 0
                || key == null || key.length == 0
                || iv == null || iv.length == 0
                || transformation == null || transformation.length() == 0) {
            throw (new InvalidParameterException());
        }

        AlgorithmParameterSpec ivSpec = new IvParameterSpec(iv);
        SecretKeySpec newKey = new SecretKeySpec(key, "AES");
        Cipher cipher = Cipher.getInstance(transformation);
        cipher.init(Cipher.ENCRYPT_MODE, newKey, ivSpec);
        return Base64.encode(cipher.doFinal(data), Base64.DEFAULT);
    }

}

2. Usage

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;

import java.util.Arrays;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewById(R.id.aes_btn_encryption).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });

        findViewById(R.id.aes_btn_decryption).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });

        // Unsupported key size: 15 bytes
        // expected IV length of 16 but was 8

        try {
            String originalString = "Hello";

            byte[] encryptedData = EncryptUtil.encryptAndBase64Encode(originalString.getBytes(), "1234567812345678".getBytes(), "1234567812345678".getBytes(), "AES/CBC/PKCS5Padding");
            byte[] decryptedData = EncryptUtil.decryptBase64EncodeData(encryptedData, "1234567812345678".getBytes(), "1234567812345678".getBytes(), "AES/CBC/PKCS5Padding");

            String decryptedString = new String(decryptedData);
            String encryptedString = new String(encryptedData);

            if (Arrays.equals(encryptedData, encryptedData)) {
                Log.d("MainActivity", "onCreate: Good job!");
            }

            Log.d("MainActivity", "originalString = " + originalString + ", decryptedString = " + decryptedString + ", encryptedString = " + encryptedString);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

3. 小解

1. Android AES 加密时加密的key和iv(bytes)的长度需要>= 16
2. 加密位数要求iv(bytes)的长度：16 =>128, 24 => 192, 32 => 256