Skip to main content

Encrypt Decrypt data using AES in Java

AES stands for Advanced Encryption Standard. AES is an Symmetric Key Algorithm, that means key used for encrypting the data, same key will be used for decryption of the encrypted data. This algorithm supplants DES algorithm. This post shows how to use AES algorithm in Java to encrypt and decrypt data.
Encrypting Data-

 
import java.security.GeneralSecurityException;

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

public class AESTest1 {

 public static void main(String[] args) throws GeneralSecurityException {
  KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
  keyGenerator.init(128);
  
  SecretKey key = keyGenerator.generateKey();
  
  Cipher cipher = Cipher.getInstance("AES");
  cipher.init(Cipher.ENCRYPT_MODE, key);
  
  byte encryptedData[] = cipher.doFinal(args[0].getBytes());
 }

}
 
In above example we have used KeyGenerator class, which generates key for encrypting data, as we are using AES which is an Symmetric key algorithm we will need this key again while decrypting data.

getInstance method of KeyGenerator class takes String as arguments where we provide the name of the algorithm depending upon which we get the KeyGenerator object.
After that we have called init method of KeyGenerator object which tells key generator that we want to generate keys with the size of 128 bit.
Then we are creating new instance of Cipher using getInstance method where we are passing the name of algorithm to transform our data.
Then we are telling Cipher to initiate in Encryption mode and use the specified SecretKey by calling


cipher.init(Cipher.ENCRYPT_MODE, key);

Then to encrypt our data we are passing our data(args[0]) to doFinal method and we get encryptedData as our encrypted data.
To decrypt encrypted data we just need to initiate Cipher in decrypt mode using following code

 cipher.init(Cipher.DECRYPT_MODE, key);
 String originalData = new String(cipher.doFinal(encryptedData));

In above example we have used KeyGenerator class which generated a secret key for us, but what if we want to use our own secret key?
Consider following example-
import java.security.GeneralSecurityException;
import java.security.MessageDigest;

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

public class AESTest1 {

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

  MessageDigest md5 = MessageDigest.getInstance("MD5");
  md5.update("key".getBytes());
  
  SecretKeySpec key = new SecretKeySpec(md5.digest(), "AES");
  
  Cipher cipher = Cipher.getInstance("AES");
  cipher.init(Cipher.ENCRYPT_MODE, key);
  
  byte encryptedData[] = cipher.doFinal("Sachin".getBytes());
 }

}

In above example we have used MessageDigest to generate the hash for our key. SecretKeySpec class is an implementation of Key interface which allows to create secret keys using our data, in our case "key" string.
In our example we have used keys with 128 bit size, in some countries there is restriction on the size of keys. If you want to use keys with more than 128bit such as 256bit then you need to download

Unlimited Strength Jurisdiction Policy Files 6 from this link and paste/replace them in lib->security directory of your JRE installation directory. Otherwise you will get


java.security.InvalidKeyException: Illegal key size

exception.

Comments

  1. How do you encrypt and decrypt a file with AES symmetric key? Thx

    ReplyDelete

Post a Comment

Popular posts from this blog

Spring AOP : JDK Proxy vs CGLib Proxy

Spring framework is one of the most widely used framework in Enterprise application development. It has so many features such as Dependency injection, Data access integration, MVC, AOP which takes care of most of the boilerplate part of project, and developers can then focus on business logic only.

One of the important feature in Spring is AOP. It is used by almost every enterprise application which is being developed using Spring.

AOP So what is AOP? Definition of AOP -
Aspect oriented programming is a programming paradigm which aims to increase modularity by allowing the separation of cross cutting concerns. Well, my understanding of AOP is - AOP allows us to introduce/join new modules in your project at pre-specified dynamic locations without having to code for it. Traditional examples of AOP is Transaction management, logging etc. You can read more about AOP at here.

This article is for those who know AOP, have used AOP in their projects but do not know how Spring or other DI fra…

Java Tools Plugin for Notepad++

This post and the plugin is outdated. Please use plugin from this link which is updated and allows customization of shortcut key mappings and much more.
Notepad++ is a great free editor. I like notepad++ because its a light weight editor and loads instantly. I use notepad++ for editing many files everyday. One plugin I always wanted was a plugin which lets me compile my java files and execute them from editor itself, but I couldn't find it so I wrote a myself. This plugin can be downloaded from this link.
I am working on this plugin to make it more effective, so that if user have more than one installations of JDK or JRE then user should be able to choose which one to use etc.
This is a simple plugin which has two commands-
Compile - compiles a java file.
Run - executes a java file.
For using this plugin Java must be installed on the system.

Notepad++ Compile and Run Java Programs

Notepad++ is a great file editor. It has many features. The most important feature which I like about Notepad++ is its light weight. It loads up so quickly, that's great. It also provides syntax highlighting for many languages. I use notepad++ to edit general files as well as my simple Java programs.
Although notepad++ provides functionality to run external programs, I prefer NppJavaTools plugin to compile and run Java programs using notepad++.
You can download NppJavaTools plugin from this page - NppJavaTools.

Installation
Installation of plugins in notepad++ is very simple process. All you have to do is copy plugin dll into plugins folder of notepad++ installation directory and restart the notepad++.

Features
This plugin provides following features,


Compile and run your Java files within Notepad++Set custom hotkeys for compiling and running Java CodeLibrary support Compile and RunThis function allows you to run your Java programs to compile and run from Notepad++. Set Custom hotkeysThi…