Encrypt/Decrypt with with AES/ECB/PKCS7Padding

In this example we shall show you how to encrypt/decrypt data with the AES/ECB/PKCS 7Padding. To encrypt data using the AES algorithm,in ECB mode and with PKCS7Padding one should perform the following steps:

  • Create a byte array to be used as input to be encrypted and a byte array to be used as a key.
  • Create a new SecretKeySpec for the AES algorithm.
  • Create a new Cipher for the “AES/ECB/PKCS7Padding” transformation, using an org.bouncycastle.jce.provider.BouncyCastleProvider().
  • Initialize the cipher in encryption mode using the key, with the init(int opmode, Key key) API method.
  • Do the encryption. Create a new byte array. Its length is set by the bytes to be returned after the encryption, with the getOutputSize(int inputLen) API method. Invoke the update(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset) and doFinal(byte[] output, int outputOffset) API methods of the Cipher for the encryption.
  • Initialize the cipher in decryption mode and do the decryption, using the same steps as in the encryption.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;

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

 * Basic symmetric encryption example
public class Main {

    public static void main(String[] args) throws Exception {

  Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

  byte[] input = "".getBytes();

  byte[] keyBytes = new byte[]{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,

0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17};

  SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");

  Cipher cipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC");

  System.out.println(new String(input));

  // encryption pass

  cipher.init(Cipher.ENCRYPT_MODE, key);

  byte[] cipherText = new byte[cipher.getOutputSize(input.length)];

  int ctLength = cipher.update(input, 0, input.length, cipherText, 0);

  ctLength += cipher.doFinal(cipherText, ctLength);

  System.out.println(new String(cipherText).getBytes("UTF-8").toString());


  // decryption pass

  cipher.init(Cipher.DECRYPT_MODE, key);

  byte[] plainText = new byte[cipher.getOutputSize(ctLength)];

  int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0);

  ptLength += cipher.doFinal(plainText, ptLength);

  System.out.println(new String(plainText));


Output: [B@ebe9f73 32

This was an example of how to encrypt/decrypt data with the AES/ECB/PKCS 7Padding in Java.

Ilias Tsagklis

Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.
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