Encrypt and Decrypt Images Using Java

Hi, Most of you would find it useful to Encrypt a special picture of yours such that only you can view it. By using JCE(Java Cryptography Extension) classes, this becomes very simple. As I have already done before using Java to encrypt a String is very simple. If you are new to this, please read the article which I had already posted named "Java Encryption and Decryption"
at "http://ruchiram4.blogspot.com/2009/04/java-encryption-and-decryption.html"
Also, you need to have a basic understanding of Java IO. If you are new, it is better to read the Sun Java tutorial on IO.

Before we move on, lets recall the basic steps in Encrypting plaintext.

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1. Creating an instance of "Cipher" object and setting the mode of Encryption (Eg: AES, DES)

2. Generating a key by using a KeyGenerator object.

3. Setting the mode of Cipher operation on the Cipher object. As we intent to Encrypt, we simply set it by setting a property of Cipher object by calling its "init" method.

4. Calling the "doFinal" method of the Cipher object

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Now, Encrypting an image is pretty much similar except, we first need to read the image from the hard disk as a File Input. Initializing steps are the same for the Cipher object and Key.
We first initialize a Cipher object for Encrypting as we have done. We pass the Cipher object with the necessary key used for Encryption. This can be done by calling the "init" method of the Cipher object and passing the necessary parameters.
Once we initialize a Cipher Object, we pass the initialized Cipher object to a "CipherInputStream" object. (A CipherInputStream object is an object provided by JCE. We need to show which file to read from and which cipher object to use). Then we can simply read through the CipherInputStream object and Encryption is done while reading from the CipherInputStream object.

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Creating a Cipher object and a Key

Cipher cipher=Cipher.getInstance("AES");
KeyGenerator keyGen=KeyGenerator.getInstance("AES");
Key key=keyGen.generateKey();

Now, we initialize the Cipher object

cipher.init(Cipher.ENCRYPT_MODE, key);

Create a CipherInputStream object by passing the realavent image to be Encrypted along with the Cipher object which we initilalized

cipherIn=new CipherInputStream(new FileInputStream(new File("./image.jpg")), cipher);

Now, we create an output stream for writing back the Encrypted image to disk

FileOutputStream fos=new FileOutputStream(new File("./filename.jpg"));

Now, we read from the CipherInputStream object just like reading from a FileInputStream.
We simply write back the Encrypted file to the Disk

int i;
while((i=cipherIn.read())!=-1){
fos.write(i);
}

NOTE: It is more efficient to use Buffer objects when doing file IO. But, in order to make things clear and simple, I ommited them.

Decrypting is very similar. You first need to call make another Cipher object and call init method with parameter for Decryption. This can be done as follows

cipher.init(Cipher.DECRYPT_MODE, key);

NOTE: YOU MUST USE THE SAME KEY GENERATED WHICH WAS USED FOR ENCRYPTING. OTHERWISE, YOU MAY NOT BE ABLE TO DECRYPT IT BACK.

Now, we can use a CipherInputStream object to read the Encrypted image. Since, we have set the mode to decryption, the CipherInputStream would basically decrypt as it reads from the Encrypted image.