AES Encryption/Decrypton

[john price]

This is the first time I have tried file encryption/decryption (I have some experience with network encryption/decryption). I tried to create a program that would save an AES key (128 bit to test) to a file. Then, a separate program would read this file and convert it back to the string. I suspect the second program has to know some kind of key of the first, but I really don't know what I am doing. Here is the encrypting program with comments at the top :

EncryptTest.java (It is 41 lines, seems to have no errors, and seems to work. It outputs a file named "psswd" with 33 seemingly random characters each time this program is ran)

import java.security.*;
   import javax.crypto.*;
   import javax.crypto.spec.*;
   import java.io.*;

	public class EncryptTest {
	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 {
KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey skey = kgen.generateKey();
byte[] raw = skey.getEncoded();
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] encrypted = cipher.doFinal((args.length == 0 ? "This is a test" : args [0]).getBytes());
	try{
  FileWriter fstream = new FileWriter("psswd");
  BufferedWriter out = new BufferedWriter(fstream);
  out.write(asHex(encrypted));
  //Close the output stream
  out.close();
  }
catch (Exception e){
  System.err.println("Error: " + e.getMessage());
  }
}
}

DecryptTest.java (It is 35 lines, doesn't seems to work, and produces one error)

import java.security.*;
   import javax.crypto.*;
   import javax.crypto.spec.*;
   import java.io.*;
	public class DecryptTest {
	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 {
Cipher cipher = Cipher.getInstance("AES");
cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey skey = kgen.generateKey();
byte[] raw = skey.getEncoded();
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
InputStream is = new FileInputStream(new File("psswd"));
byte[] encrypted = new byte[(int)new File("psswd").length()];
is.read(encrypted);
byte[] original = cipher.doFinal(encrypted);
String originalString = new String(original);
System.out.println(original);
}
}

Error output from "DecryptTest" program :

cc11rocks@cc11rocks-1005HA ~/Desktop $ java DecryptTest
Exception in thread "main" java.security.InvalidKeyException: Parameters missing
	at com.sun.crypto.provider.CipherCore.init(CipherCore.java:388)
	at com.sun.crypto.provider.AESCipher.engineInit(AESCipher.java:190)
	at javax.crypto.Cipher.implInit(Cipher.java:682)
	at javax.crypto.Cipher.chooseProvider(Cipher.java:737)
	at javax.crypto.Cipher.init(Cipher.java:989)
	at javax.crypto.Cipher.init(Cipher.java:935)
	at DecryptTest.main(DecryptTest.java:27)

Thank you,
John Price

[john price]

I also tried another way. I kicked the padding lines on both the Encryption and Decryption programs (cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");). Here is the new Decryption program that I tried. It gave me a new error :
DecryptTest (35 lines)

import java.security.*;
   import javax.crypto.*;
   import javax.crypto.spec.*;
   import java.io.*;
	public class DecryptTest {
	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 {
Cipher cipher = Cipher.getInstance("AES");
KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey skey = kgen.generateKey();
byte[] raw = skey.getEncoded();
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
InputStream in = new FileInputStream(new File("psswd"));
byte[] encrypted = new byte[(int)new File("psswd").length()];
in.read(encrypted);
in.close();
byte[] original = cipher.doFinal(encrypted);
String originalString = new String(original);
System.out.println(original);
}
}

Error :

cc11rocks@cc11rocks-1005HA ~/Desktop $ java DecryptTest
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded
	at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:811)
	at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
	at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:317)
	at javax.crypto.Cipher.doFinal(Cipher.java:1813)
	at DecryptTest.main(DecryptTest.java:31)

[Tim Moores]

A few observations:

It seems that you don't save the key - the code creates a new one for each encryption and decryption. In other words, you will never be able to decrypt.

It also looks like you're running the encrypted data through the asHex method (why? you can store binary data in a file) before saving it in a file, but there's no corresponding decoding being done before decryption.

"new String(original)" - don't do this. Never use the String(byte[]) constructor without specifying the encoding; it's just asking for trouble. Conversely, never use the String.getBytes() method without specifying the encoding.

[john price]

I tried to super simplify it by coming up with a static key. I will eventually make this into a password entered by GUI or command line, which will be different every time. Anyway, I bought the code down to less than 25 lines each. I have to add the type of encryption somewhere (128, 196, or 256), I just don't know where. Thanks for your help!

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;

public class EncryptTest {
	public static void main(String[] args) throws Exception {
		SecretKeySpec skeySpec = new SecretKeySpec("sometestjavarock".getBytes(), "AES");
		System.out.println(skeySpec.getAlgorithm());
		System.out.println(skeySpec.getFormat());
		System.out.println(skeySpec.toString());
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		byte[] encrypted = cipher.doFinal((args.length == 0 ? "This is a test" : args [0]).getBytes());
		try {
			OutputStream out = new FileOutputStream("psswd");
			out.write(encrypted);
			out.close();
		}
		catch (Exception e){
			System.err.println("Error: " + e.getMessage());
		}
	}
}

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;
   
public class DecryptTest {
	public static void main(String[] args) throws Exception {
		Cipher cipher = Cipher.getInstance("AES");
		SecretKeySpec skeySpec = new SecretKeySpec("sometestjavarock".getBytes(), "AES");
		System.out.println(skeySpec.getAlgorithm());
		System.out.println(skeySpec.getFormat());
		System.out.println(skeySpec.toString());
		cipher.init(Cipher.DECRYPT_MODE, skeySpec);
		InputStream in = new FileInputStream(new File("psswd"));
		byte[] encrypted = new byte[(int)new File("psswd").length()];
		in.read(encrypted);
		in.close();
		byte[] original = cipher.doFinal(encrypted);
		String originalString = new String(original);
		System.out.println(original);
	}
}

cc11rocks@cc11rocks-1005HA ~/Desktop $ javac EncryptTest.java 
cc11rocks@cc11rocks-1005HA ~/Desktop $ java EncryptTest 
AES
RAW
javax.crypto.spec.SecretKeySpec@14a86
cc11rocks@cc11rocks-1005HA ~/Desktop $ javac DecryptTest.java 
cc11rocks@cc11rocks-1005HA ~/Desktop $ java DecryptTest 
AES
RAW
javax.crypto.spec.SecretKeySpec@14a86
[B@b6ece5
cc11rocks@cc11rocks-1005HA ~/Desktop $ 

Here is what I've come to. Everything is equal, it's just not printing out the string. What do I need to convert to to see the string?

Thanks,
John Price

[Tim Moores]

Instead of CBC, use ECB. And, of course, don't print out the byte array, print out the string. (And, again, don't use "new String(byte[])".)

You can use AES-256 instead of AES-128 by using a 32 byte (= 256 bit) key instead of a 16 byte (= 128 bit) key. AES-192 presumably takes a 24 byte key.

[john price]

Instead of CBC, use ECB. And, of course, don't print out the byte array, print out the string. (And, again, don't use "new String(byte[])".)

1. Could you please tell me how to switch from CBC to ECB?
2. I can't seem to figure out how to print out the value of that byte array. I feel like such a n00b after programming for a year, but I haven't been programming for a few months so please excuse me.

Thanks for your help,
John Price

EDIT : I am now doing getBytes("UTF-8") so that should clear up future problems. In this case, it's still printing out the byte[] location or whatever

EDIT 2 : I am such an idiot. I forgot to print out the string, not the byte array. I see what you are saying now. What should I use to convert it from byte array to string?

[Tim Moores]

1. Could you please tell me how to switch from CBC to ECB?

Search "CBC", replace by "ECB".

I forgot to print out the string, not the byte array. I see what you are saying now. What should I use to convert it from byte array to string?

? The code already performs the conversion, albeit, as I pointed out, using a constructor that you should not be using. Note also, as I said before, that you should not be using String.getBytes() - which the code does in three places. Here, too, should you specify the encoding.

[john price]

This is what you were saying I was supposed to do (below) ? I didn't look into how to replace it much yet, but this is what I got for those of you who are really wondering how to do it :

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;

public class EncryptTest {
	public static void main(String[] args) throws Exception {
		String code = args[0];
		String toEncode = args[1];
		SecretKeySpec skeySpec = new SecretKeySpec(code.getBytes("UTF-8"), "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		byte[] encrypted = cipher.doFinal(toEncode.getBytes("UTF-8"));
		try {
			OutputStream out = new FileOutputStream("psswd");
			out.write(encrypted);
			out.close();
		}
		catch (Exception e){
			System.err.println("Error: " + e.getMessage());
		}
	}
}

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;
   
public class DecryptTest {
	public static void main(String[] args) throws Exception {
		String code = args[0];
		Cipher cipher = Cipher.getInstance("AES");
		SecretKeySpec skeySpec = new SecretKeySpec(code.getBytes("UTF-8"), "AES");
		cipher.init(Cipher.DECRYPT_MODE, skeySpec);
		InputStream in = new FileInputStream(new File("psswd"));
		byte[] encrypted = new byte[(int)new File("psswd").length()];
		in.read(encrypted);
		in.close();
		byte[] original = cipher.doFinal(encrypted);
		String originalString = new String(original, "UTF-8");
		System.out.println(originalString);
	}
}

cc11rocks@cc11rocks-1005HA ~/Desktop $ javac EncryptTest.java
cc11rocks@cc11rocks-1005HA ~/Desktop $ javac DecryptTest.java
cc11rocks@cc11rocks-1005HA ~/Desktop $ java EncryptTest qwertyuiopasdfgh HelloUI
cc11rocks@cc11rocks-1005HA ~/Desktop $ java DecryptTest qwertyuiopasdfgh //Right Password/Encryption key
HelloUI
cc11rocks@cc11rocks-1005HA ~/Desktop $ java DecryptTest qwertyuiopasdfgw //Wrong Password/Encryption key
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded
	at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:811)
	at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
	at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:317)
	at javax.crypto.Cipher.doFinal(Cipher.java:1813)
	at DecryptTest.main(DecryptTest.java:16)
cc11rocks@cc11rocks-1005HA ~/Desktop $ 

Thank you,
John Price

[john price]

Here is my finished product. Thank you guys so much for your help. I will implement a very modified version of this into one of my major projects I have been working on. By the way, EncryptTest could be more efficient, I just took the easy way with the nullifying of args[0]. If you are confused, look at the code below. The programs take command line input such as displayed here :

java EncryptTest [key] [string] [string] [string] [asManyMoreStringsAsYouWant]
java DecryptTest [key]

Here is a live example :

cc11rocks@cc11rocks-1005HA ~/Desktop $ javac EncryptTest.java
cc11rocks@cc11rocks-1005HA ~/Desktop $ javac DecryptTest.java 
cc11rocks@cc11rocks-1005HA ~/Desktop $ java EncryptTest qwertyuiopasdfgh Hi Hi Hello
cc11rocks@cc11rocks-1005HA ~/Desktop $ java DecryptTest qwertyuiopasdfgh
Hi
Hi
Hello
cc11rocks@cc11rocks-1005HA ~/Desktop $ 

Here is EncryptTest.java and DecryptTest.java :
EncryptTest.java :

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;

public class EncryptTest {
String code;
	public static void main(String[] args) throws Exception {
	EncryptTest tester = new EncryptTest();
	tester.start(args);
	}
	public void start (String[] args) {
	code = args[0];
		args[0] = null;
		for (String lines : args) {
			if (lines != null) {
				if (lines == args[1]) {
					createFile(lines);
				}
				else {
					addToFile(lines);
				}
			}
		}
	}
	public void createFile (String toEncode) {
	try {
	SecretKeySpec skeySpec = new SecretKeySpec(code.getBytes("UTF-8"), "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		byte[] encrypted = cipher.doFinal(toEncode.getBytes("UTF-8"));
			OutputStream out = new FileOutputStream("psswd");
			out.write(encrypted);
			out.close();
		}
		catch (Exception e){
			System.err.println("Error: " + e.getMessage());
		}
	}
	public void addToFile(String toEncode) {
	try {
	SecretKeySpec skeySpec = new SecretKeySpec(code.getBytes("UTF-8"), "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		byte[] encrypted = cipher.doFinal(toEncode.getBytes("UTF-8"));
		byte[] spacer = cipher.doFinal(System.getProperty("line.separator").getBytes("UTF-8"));
			OutputStream out = new FileOutputStream("psswd", true);
			out.write(spacer);
			out.write(encrypted);
			out.close();
		}
		catch (Exception e){
			System.err.println("Error: " + e.getMessage());
		}
	}
}

DecryptTest.java

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;
   
public class DecryptTest {
	public static void main(String[] args) throws Exception {
		String code = args[0];
		Cipher cipher = Cipher.getInstance("AES");
		SecretKeySpec skeySpec = new SecretKeySpec(code.getBytes("UTF-8"), "AES");
		cipher.init(Cipher.DECRYPT_MODE, skeySpec);
		InputStream in = new FileInputStream(new File("psswd"));
		byte[] encrypted = new byte[(int)new File("psswd").length()];
		in.read(encrypted);
		in.close();
		byte[] original = cipher.doFinal(encrypted);
		String originalString = new String(original, "UTF-8");
		System.out.println(originalString);
	}
}

Thanks a lot guys!
John Price