Symmetric encryption example

With this example we are going to demonstrate how to make a symmetric encryption and decryption. In symmetric encryption the same key is used for both encryption of plaintext and decryption of ciphertext. In short, to make a symmetric encryption you should:

  • Create a byte array from the initial password and a byte array from the initial key.
  • Create a new SecretKeySpec from the key byte array, using the AES algorithm.
  • Create a new Cipher for the AES/ECB/NoPadding transformation and initialize it in
    encryption mode, with the specified key, using the getInstance(String transformation) and init(int opmode, Key key)
    API methods.
  • Make the encryption, with the update(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset) and doFinal(byte[] output, int outputOffset) API methods. The result is a new byte array with the encrypted password.
  • Initialize the cipher in decryption mode, using the same key.
  • Make the decryption of the encrypted byte array. The result will be a decrypted byte array,

as shown in the code snippet below.

package com.javacodegeeks.snippets.core;

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

public class Main {

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

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

  byte[] password = "JavaJavaJavaJava".getBytes("UTF-8");

  byte[] pkey = "keykeykekeykeykekeykeykekeykeyke".getBytes("UTF-8"); 

  SecretKeySpec secretKey = new SecretKeySpec(pkey, "AES");

  Cipher c = Cipher.getInstance("AES/ECB/NoPadding");

  System.out.println("User password(plaintext) : " + new String(password));

  // encrypt password

  byte[] cText = new byte[password.length];

  c.init(Cipher.ENCRYPT_MODE, secretKey);

  int ctLen = c.update(password, 0, password.length, cText, 0);

  ctLen += c.doFinal(cText, ctLen);

  System.out.println("Password encrypted: " + cText.toString().getBytes("UTF-8").toString() + " bytes: " + ctLen);

  // decrypt password

  byte[] plainText = new byte[ctLen];

  c.init(Cipher.DECRYPT_MODE, secretKey);

  int plen = c.update(cText, 0, ctLen, plainText, 0);

  plen += c.doFinal(plainText, plen);

  System.out.println("User password(plaintext) : " + new String(plainText) + " bytes: " + plen);


User password(plaintext) : JavaJavaJavaJava
Password encrypted: [B@64b045f4 bytes: 16
User password(plaintext) : JavaJavaJavaJava bytes: 16

This was an example of how to make symmetric encryption in Java.

Byron Kiourtzoglou

Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.
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