Write a JAVA program to implement the Rijndael algorithm | Rijndael algorithm in JAVA | Cryptography

AIM: Write a C/JAVA program to implement the Rijndael algorithm logic.

HARDWARE AND SOFTWARE REQUIREMENT:

1. Intel based Desktop PC: - RAM of 512 MB

2. Notepad/Notepad ++ editor  and Command Prompt or

3. IntelliJ IDEA Community Edition

THEORY:

Ø  Rijndael is advanced version of AES(which is defined for fixed block size i.e.128 bit) which defined for variable length block sizes i.e.128,192 and 256 bits

Ø  If a different block size between encryption and decryption is used, then it is not possible to recover the original plaintext.

Ø  The Rijndael algorithm is a new generation symmetric encryption algorithm.

Ø  It is block cipher algorithm data handling happened in 128-bits blocks,variable key length & variable round number.

Ø  Encryption under Rijndael is achieved through a series of matrix transformations . Each transformation is known as a round

Ø  Rijndael does not use a fixed number of rounds, the number of rounds are dependant on key/block sizes, as follows:

·     For key/block size 128 bits , 9 rounds are required.

·     For key/block size 192 bits, 11 rounds are required.

·     For key/block size 256 bits, 13 rounds are required.

SOURCE CODE:
import javax.crypto.*;
import javax.crypto.spec.*;

class Rijndael  {

    private 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 = "ONLINE SMART TRAINER";
        //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 in Hexadecimal: " + asHex(original));
        System.out.println("Original String: " + originalString);
    }
}

OUTPUT:

VIVA QUESTIONS:

1. What is JAVA?
2. What is rijndael Algorithm?
3. What is Encryption?
4. What is Decryption?