Using the Java Cryptographic Extensions

package org.owasp.java.crypto;

import java.security.SecureRandom;
import java.security.NoSuchAlgorithmException;

/**
 * @author Joe Prasanna Kumar
 * This program provides the functionality for Generating a Secure Random Number.
 *
 * There are 2 ways to generate a  Random number through SecureRandom.
 * 1. By calling nextBytes method to generate Random Bytes
 * 2. Using setSeed(byte[]) to reseed a Random object
 *
 */


public class SecureRandomGen {

    /**
     * @param args
     */
    public static void main(String[] args) {
        try {
            // Initialize a secure random number generator
            SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");

            // Method 1 - Calling nextBytes method to generate Random Bytes
            byte[] bytes = new byte[512];
            secureRandom.nextBytes(bytes);

            // Printing the SecureRandom number by calling secureRandom.nextDouble()
            System.out.println(" Secure Random # generated by calling nextBytes() is " + secureRandom.nextDouble());

            // Method 2 - Using setSeed(byte[]) to reseed a Random object
            int seedByteCount = 10;
            byte[] seed = secureRandom.generateSeed(seedByteCount);

            secureRandom.setSeed(seed);

            System.out.println(" Secure Random # generated using setSeed(byte[]) is  " + secureRandom.nextDouble());

        } catch (NoSuchAlgorithmException noSuchAlgo)
        {
            System.out.println(" No Such Algorithm exists " + noSuchAlgo);
        }
    }

}

package org.owasp.java.crypto;

import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

import java.util.Base64;

/**
 * @author Joe Prasanna Kumar
 * This program provides the following cryptographic functionalities
 * 1. Encryption using AES
 * 2. Decryption using AES
 *
 * High Level Algorithm :
 * 1. Generate a AES key (specify the Key size during this phase)
 * 2. Create the Cipher
 * 3. To Encrypt : Initialize the Cipher for Encryption
 * 4. To Decrypt : Initialize the Cipher for Decryption
 *
 *
 */

public class AES {
    public static void main(String[] args) {

        String strDataToEncrypt = new String();
        String strCipherText = new String();
        String strDecryptedText = new String();

        try {
            /**
             * Step 1. Generate an AES key using KeyGenerator Initialize the
             * keysize to 128 bits (16 bytes)
             *
             */
            KeyGenerator keyGen = KeyGenerator.getInstance("AES");
            keyGen.init(128);
            SecretKey secretKey = keyGen.generateKey();

            /**
             * Step 2. Generate an Initialization Vector (IV)
             *      a. Use SecureRandom to generate random bits
             *         The size of the IV matches the blocksize of the cipher (128 bits for AES)
             *      b. Construct the appropriate IvParameterSpec object for the data to pass to Cipher's init() method
             */

            final int AES_KEYLENGTH = 128;  // change this as desired for the security level you want
            byte[] iv = new byte[AES_KEYLENGTH / 8];    // Save the IV bytes or send it in plaintext with the encrypted data so you can decrypt the data later
            SecureRandom prng = new SecureRandom();
            prng.nextBytes(iv);

            /**
             * Step 3. Create a Cipher by specifying the following parameters
             *      a. Algorithm name - here it is AES
             *      b. Mode - here it is CBC mode
             *      c. Padding - PKCS5
             */

            Cipher aesCipherForEncryption = Cipher.getInstance("AES/CBC/PKCS5PADDING"); // Must specify the mode explicitly as most JCE providers default to ECB mode!!

            /**
             * Step 4. Initialize the Cipher for Encryption
             */

            aesCipherForEncryption.init(Cipher.ENCRYPT_MODE, secretKey,
                    new IvParameterSpec(iv));

            /**
             * Step 5. Encrypt the Data
             *      a. Declare / Initialize the Data. Here the data is of type String
             *      b. Convert the Input Text to Bytes
             *      c. Encrypt the bytes using doFinal method
             */
            strDataToEncrypt = "Hello World of Encryption using AES ";
            byte[] byteDataToEncrypt = strDataToEncrypt.getBytes();
            byte[] byteCipherText = aesCipherForEncryption
                    .doFinal(byteDataToEncrypt);
            strCipherText = Base64.getEncoder().withoutPadding().encodeToString(byteCipherText);
            System.out.println("Cipher Text generated using AES is "
                    + strCipherText);

            /**
             * Step 6. Decrypt the Data
             *      a. Initialize a new instance of Cipher for Decryption (normally don't reuse the same object)
             *         Be sure to obtain the same IV bytes for CBC mode.
             *      b. Decrypt the cipher bytes using doFinal method
             */

            Cipher aesCipherForDecryption = Cipher.getInstance("AES/CBC/PKCS5PADDING"); // Must specify the mode explicitly as most JCE providers default to ECB mode!!

            aesCipherForDecryption.init(Cipher.DECRYPT_MODE, secretKey,
                    new IvParameterSpec(iv));
            byte[] byteDecryptedText = aesCipherForDecryption
                    .doFinal(byteCipherText);
            strDecryptedText = new String(byteDecryptedText);
            System.out
                    .println(" Decrypted Text message is " + strDecryptedText);
        }

        catch (NoSuchAlgorithmException noSuchAlgo) {
            System.out.println(" No Such Algorithm exists " + noSuchAlgo);
        }

        catch (NoSuchPaddingException noSuchPad) {
            System.out.println(" No Such Padding exists " + noSuchPad);
        }

        catch (InvalidKeyException invalidKey) {
            System.out.println(" Invalid Key " + invalidKey);
        }

        catch (BadPaddingException badPadding) {
            System.out.println(" Bad Padding " + badPadding);
        }

        catch (IllegalBlockSizeException illegalBlockSize) {
            System.out.println(" Illegal Block Size " + illegalBlockSize);
        }

        catch (InvalidAlgorithmParameterException invalidParam) {
            System.out.println(" Invalid Parameter " + invalidParam);
        }
    }
}

package org.owasp.crypto;

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

import java.security.NoSuchAlgorithmException;
import java.security.InvalidKeyException;
import java.security.InvalidAlgorithmParameterException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.BadPaddingException;
import javax.crypto.IllegalBlockSizeException;

/**
 * @author Joe Prasanna Kumar
 * This program provides the following cryptographic functionalities
 * 1. Encryption using DES
 * 2. Decryption using DES
 *
 * The following modes of DES encryption are supported by SUNJce provider
 * 1. ECB (Electronic code Book) - Every plaintext block is encrypted separately
 * 2. CBC (Cipher Block Chaining) - Every plaintext block is XORed with the previous ciphertext block
 * 3. PCBC (Propogating Cipher Block Chaining) -
 * 4. CFB (Cipher Feedback Mode) - The previous ciphertext block is encrypted and this enciphered block is XORed with the plaintext block to produce the corresponding ciphertext block
 * 5. OFB (Output Feedback Mode) -
 *
 *  High Level Algorithm :
 * 1. Generate a DES key
 * 2. Create the Cipher (Specify the Mode and Padding)
 * 3. To Encrypt : Initialize the Cipher for Encryption
 * 4. To Decrypt : Initialize the Cipher for Decryption
 *
 * Need for Padding :
 * Block ciphers operates on data blocks on fixed size n.
 * Since the data to be encrypted might not always be a multiple of n, the remainder of the bits are padded.
 * PKCS#5 Padding is what will be used in this program
 *
 */

public class DES {
    public static void main(String[] args) {

        String strDataToEncrypt = new String();
        String strCipherText = new String();
        String strDecryptedText = new String();

        try{
        /**
         *  Step 1. Generate a DES key using KeyGenerator
         *
         */
        KeyGenerator keyGen = KeyGenerator.getInstance("DES");
        SecretKey secretKey = keyGen.generateKey();

        /**
         *  Step2. Create a Cipher by specifying the following parameters
         *          a. Algorithm name - here it is DES
         *          b. Mode - here it is CBC
         *          c. Padding - PKCS5Padding
         */

        Cipher desCipher = Cipher.getInstance("DES/CBC/PKCS5Padding"); /* Must specify the mode explicitly as most JCE providers default to ECB mode!! */

        /**
         *  Step 3. Initialize the Cipher for Encryption
         */

        desCipher.init(Cipher.ENCRYPT_MODE,secretKey);

        /**
         *  Step 4. Encrypt the Data
         *          1. Declare / Initialize the Data. Here the data is of type String
         *          2. Convert the Input Text to Bytes
         *          3. Encrypt the bytes using doFinal method
         */
        strDataToEncrypt = "Hello World of Encryption using DES ";
        byte[] byteDataToEncrypt = strDataToEncrypt.getBytes();
        byte[] byteCipherText = desCipher.doFinal(byteDataToEncrypt);
        strCipherText = Base64.getEncoder().withoutPadding().encodeToString(byteCipherText);
        System.out.println("Cipher Text generated using DES with CBC mode and PKCS5 Padding is " +strCipherText);

        /**
         *  Step 5. Decrypt the Data
         *          1. Initialize the Cipher for Decryption
         *          2. Decrypt the cipher bytes using doFinal method
         */
        desCipher.init(Cipher.DECRYPT_MODE,secretKey,desCipher.getParameters());
         //desCipher.init(Cipher.DECRYPT_MODE,secretKey);
        byte[] byteDecryptedText = desCipher.doFinal(byteCipherText);
        strDecryptedText = new String(byteDecryptedText);
        System.out.println(" Decrypted Text message is " +strDecryptedText);
        }

        catch (NoSuchAlgorithmException noSuchAlgo)
        {
            System.out.println(" No Such Algorithm exists " + noSuchAlgo);
        }

            catch (NoSuchPaddingException noSuchPad)
            {
                System.out.println(" No Such Padding exists " + noSuchPad);
            }

                catch (InvalidKeyException invalidKey)
                {
                    System.out.println(" Invalid Key " + invalidKey);
                }

                catch (BadPaddingException badPadding)
                {
                    System.out.println(" Bad Padding " + badPadding);
                }

                catch (IllegalBlockSizeException illegalBlockSize)
                {
                    System.out.println(" Illegal Block Size " + illegalBlockSize);
                }

                catch (InvalidAlgorithmParameterException invalidParam)
                {
                    System.out.println(" Invalid Parameter " + invalidParam);
                }
    }

}