iud_key_imp10/Quellcodes/iud_key_rsachat/TestRSA2.java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;

import javax.crypto.Cipher;

/**
 * @author JavaDigest
 * 
 */
public class TestRSA2 {
  
  /**
  * String to hold name of the encryption algorithm.
  */
  public static final String ALGORITHM = "RSA";
  
  /**
  * String to hold the name of the private key file.
  */
  public static final String PRIVATE_KEY_FILE = "C:/keys/private.key";
  
  /**
  * String to hold name of the public key file.
  */
  public static final String PUBLIC_KEY_FILE = "C:/keys/public.key";
  
  /**
  * Generate key which contains a pair of private and public key using 1024
  * bytes. Store the set of keys in Prvate.key and Public.key files.
  * 
  * @throws NoSuchAlgorithmException
  * @throws IOException
  * @throws FileNotFoundException
  */
  public static void generateKey() {
    try {
      final KeyPairGenerator keyGen = KeyPairGenerator.getInstance(ALGORITHM);
      keyGen.initialize(1024);
      final KeyPair key = keyGen.generateKeyPair();
      
      File privateKeyFile = new File(PRIVATE_KEY_FILE);
      File publicKeyFile = new File(PUBLIC_KEY_FILE);
      
      // Create files to store public and private key
      if (privateKeyFile.getParentFile() != null) {
        privateKeyFile.getParentFile().mkdirs();
      }
      privateKeyFile.createNewFile();
      
      if (publicKeyFile.getParentFile() != null) {
        publicKeyFile.getParentFile().mkdirs();
      }
      publicKeyFile.createNewFile();
      
      // Saving the Public key in a file
      ObjectOutputStream publicKeyOS = new ObjectOutputStream(
      new FileOutputStream(publicKeyFile));
      publicKeyOS.writeObject(key.getPublic());
      publicKeyOS.close();
      
      // Saving the Private key in a file
      ObjectOutputStream privateKeyOS = new ObjectOutputStream(
      new FileOutputStream(privateKeyFile));
      privateKeyOS.writeObject(key.getPrivate());
      privateKeyOS.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
    
  }
  
  /**
  * The method checks if the pair of public and private key has been generated.
  * 
  * @return flag indicating if the pair of keys were generated.
  */
  public static boolean areKeysPresent() {
    
    File privateKey = new File(PRIVATE_KEY_FILE);
    File publicKey = new File(PUBLIC_KEY_FILE);
    
    if (privateKey.exists() && publicKey.exists()) {
      return true;
    }
    return false;
  }
  
  /**
  * Encrypt the plain text using public key.
  * 
  * @param text
  *          : original plain text
  * @param key
  *          :The public key
  * @return Encrypted text
  * @throws java.lang.Exception
  */
  public static byte[] encrypt(String text, PublicKey key) {
    byte[] cipherText = null;
    try {
      // get an RSA cipher object and print the provider
      final Cipher cipher = Cipher.getInstance(ALGORITHM);
      // encrypt the plain text using the public key
      cipher.init(Cipher.ENCRYPT_MODE, key);
      cipherText = cipher.doFinal(text.getBytes());
    } catch (Exception e) {
      e.printStackTrace();
    }
    return cipherText;
  }
  
  /**
  * Decrypt text using private key.
  * 
  * @param text
  *          :encrypted text
  * @param key
  *          :The private key
  * @return plain text
  * @throws java.lang.Exception
  */
  public static String decrypt(byte[] text, PrivateKey key) {
    byte[] dectyptedText = null;
    try {
      // get an RSA cipher object and print the provider
      final Cipher cipher = Cipher.getInstance(ALGORITHM);
      
      // decrypt the text using the private key
      cipher.init(Cipher.DECRYPT_MODE, key);
      dectyptedText = cipher.doFinal(text);
      
    } catch (Exception ex) {
      ex.printStackTrace();
    }
    
    return new String(dectyptedText);
  }
  
  /**
  * Test the EncryptionUtil
  */
  public static void main(String[] args) {
    
    try {
      
      // Check if the pair of keys are present else generate those.
      if (!areKeysPresent()) {
        // Method generates a pair of keys using the RSA algorithm and stores it
        // in their respective files
        generateKey();
      }
      
      final String originalText = "Text to be encrypted. Dies ist ein l<>ngerer Text.";
      ObjectInputStream inputStream = null;
      
      // Encrypt the string using the public key
      inputStream = new ObjectInputStream(new FileInputStream(PUBLIC_KEY_FILE));
      final PublicKey publicKey = (PublicKey) inputStream.readObject();
      final byte[] cipherText = encrypt(originalText, publicKey);
      
      // Decrypt the cipher text using the private key.
      inputStream = new ObjectInputStream(new FileInputStream(PRIVATE_KEY_FILE));
      final PrivateKey privateKey = (PrivateKey) inputStream.readObject();
      final String plainText = decrypt(cipherText, privateKey);
      
      // Printing the Original, Encrypted and Decrypted Text
      System.out.println("Private Key"+privateKey);
      System.out.println("Original: " + originalText);
      System.out.println("Encrypted: " +cipherText.toString());
      System.out.println("Decrypted: " + plainText);
      
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}