Originally Posted by neutralfox

Hello everyone,
I got a small question on encryption, actually I am trying to learn the various techniques to encrypt a message. Now I am trying AES, using the built in security package in Java. The problem is that I am having a problem with this encryption algorithm. Actually I've got a sample of the AES on the net and trying to understand the logic but I am stuck. Here's the code:

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   import java.security.*;
   import javax.crypto.*;
   import javax.crypto.spec.*;
   import java.io.*;
 
 
   public class AES {
 
 
     public static String asHex (byte buf[]) {
 
      StringBuffer strbuf = new StringBuffer(buf.length * 2);
      int i;
 
      for (i = 0; i < buf.length; i++) {
       if (((int) buf[i] & 0xff) < 0x10)
	    strbuf.append("0");
 
       strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
      }
 
      return strbuf.toString();
     }
 
     public static void main(String[] args) throws Exception {
 
       String message="AES still rocks!!";
 
       // Get the KeyGenerator
       KeyGenerator kgen = KeyGenerator.getInstance("AES");
       kgen.init(128); // 192 and 256 bits may not be available
 
 
       // Generate the secret key specs.
       SecretKey skey = kgen.generateKey();
       byte[] raw = skey.getEncoded();
 
       SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
 
 
 
       // Instantiate the cipher
       Cipher cipher = Cipher.getInstance("AES");
 
 
 
       cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
       byte[] encrypted = cipher.doFinal((args.length == 0 ? message : args[0]).getBytes());
       System.out.println("encrypted string: " + asHex(encrypted));
 
       cipher.init(Cipher.DECRYPT_MODE, skeySpec);
       byte[] original = cipher.doFinal(encrypted);
       String originalString = new String(original);
       System.out.println("Original string: " +   originalString + " " + asHex(original));
     }
   }

import java.security.*; import javax.crypto.*; import javax.crypto.spec.*; import java.io.*; public class AES { public static String asHex (byte buf[]) { StringBuffer strbuf = new StringBuffer(buf.length * 2); int i; for (i = 0; i < buf.length; i++) { if (((int) buf[i] & 0xff) < 0x10) strbuf.append("0"); strbuf.append(Long.toString((int) buf[i] & 0xff, 16)); } return strbuf.toString(); } public static void main(String[] args) throws Exception { String message="AES still rocks!!"; // Get the KeyGenerator KeyGenerator kgen = KeyGenerator.getInstance("AES"); kgen.init(128); // 192 and 256 bits may not be available // Generate the secret key specs. SecretKey skey = kgen.generateKey(); byte[] raw = skey.getEncoded(); SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); // Instantiate the cipher Cipher cipher = Cipher.getInstance("AES"); cipher.init(Cipher.ENCRYPT_MODE, skeySpec); byte[] encrypted = cipher.doFinal((args.length == 0 ? message : args[0]).getBytes()); System.out.println("encrypted string: " + asHex(encrypted)); cipher.init(Cipher.DECRYPT_MODE, skeySpec); byte[] original = cipher.doFinal(encrypted); String originalString = new String(original); System.out.println("Original string: " + originalString + " " + asHex(original)); } }

Questions:
What is the key in this program? How can I change the key?


Finally when I try the program, I've got the following results

encrypted string: 91369a3b74c6feede0eff48fcf004f67d26cdd0b4907b44fd2147a4077ded0d1
Original string: AES still rocks!! 414553207374696c6c20726f636b732121


When the message has been decrypted, what does this "414553207374696c6c20726f636b732121" means?

Thanks a lot in advance guys. I would really appreciate if you could help me on this. I just want to understand the logic behind it in order to use it later on. Until now, I have not find a more easier code than this one. If you have one which is easier, please let me now. Again, thanks



Regards,
Mike

Originally Posted by neutralfox

Hello everyone,
What is the key in this program? How can I change the key?

Originally Posted by neutralfox

When the message has been decrypted, what does this "414553207374696c6c20726f636b732121" means?