AES decrypt - Android java.security

Android examples for java.security:AES

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Description

AES decrypt

Demo Code

import java.security.SecureRandom;

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

import android.os.Build;

public class Main {

  public static String decrypt(String key, String encrypted) throws Exception {
    byte[] rawKey = getRawKey(key.getBytes());
    byte[] enc = toByte(encrypted);
    byte[] result = decrypt(rawKey, enc);
    return new String(result);
  }/*from ww w.ja v a  2  s  .  c o  m*/

  private static byte[] decrypt(byte[] key, byte[] encrypted) throws Exception {
    SecretKeySpec skeySpec = new SecretKeySpec(key, "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec);
    byte[] decrypted = cipher.doFinal(encrypted);
    return decrypted;
  }

  public static byte[] toByte(String hexString) {
    int len = hexString.length() / 2;
    byte[] result = new byte[len];
    for (int i = 0; i < len; i++)
      result[i] = Integer.valueOf(hexString.substring(2 * i, 2 * i + 2), 16).byteValue();
    return result;
  }

  private static byte[] getRawKey(byte[] seed) throws Exception {
    KeyGenerator kgen = KeyGenerator.getInstance("AES");
    SecureRandom sr = null;
    if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
      sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");
    } else if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
      sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");
    } else {
      sr = SecureRandom.getInstance("SHA1PRNG");
    }
    sr.setSeed(seed);
    kgen.init(256, sr); // 256 bits or 128 bits,192bits
    SecretKey skey = kgen.generateKey();
    byte[] raw = skey.getEncoded();
    return raw;
  }

}

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