CryptographyHelper.java

import android.util.Base64;

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

public class CryptographyHelper {

    private static final String ALGORITHM = "AES/ECB/ZeroBytePadding";

    public static String encrypt(String plaintext, String key) throws Exception {
        return Base64.encodeToString(encrypt(plaintext.getBytes("UTF-8"), key.getBytes("UTF-8"), ALGORITHM), Base64.NO_WRAP);
    }

    public static String decrypt(String ciphertext, String key) throws Exception {
        return new String(decrypt(Base64.decode(ciphertext, Base64.NO_WRAP), key.getBytes("UTF-8"), ALGORITHM), "UTF-8");
    }

    private static byte[] encrypt(byte[] plaintext, byte[] key, String algorithm) throws Exception {
        SecretKeySpec secretKeySpec = new SecretKeySpec(key, algorithm);
        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec);
        return cipher.doFinal(plaintext);
    }

    private static byte[] decrypt(byte[] ciphertext, byte[] key, String algorithm) throws Exception {
        SecretKeySpec secretKeySpec = new SecretKeySpec(key, algorithm);
        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec);
        return cipher.doFinal(ciphertext);
    }

}