Question

// can someone explain the code line by line shortly.thanks

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.util.Base64;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;

// Java 8 example for RSA encryption/decryption.
// Uses strong encryption with 2048 key size.
public class GlobalMembers {

public static void main(String[] args) throws Exception {
String plainText = "Hello World!";

// Generate public and private keys using RSA
Map<String, Object> keys = getRSAKeys();

PrivateKey privateKey = (PrivateKey) keys.get("private");
PublicKey publicKey = (PublicKey) keys.get("public");

String encryptedText = encryptMessage(plainText, privateKey);
String descryptedText = decryptMessage(encryptedText, publicKey);

System.out.println("input:" + plainText);
System.out.println("encrypted:" + encryptedText);
System.out.println("decrypted:" + descryptedText);

}

// Get RSA keys. Uses key size of 2048.
private static Map<String,Object> getRSAKeys() throws Exception {
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
keyPairGenerator.initialize(2048);
KeyPair keyPair = keyPairGenerator.generateKeyPair();
PrivateKey privateKey = keyPair.getPrivate();
PublicKey publicKey = keyPair.getPublic();

Map<String, Object> keys = new HashMap<String,Object>();
keys.put("private", privateKey);
keys.put("public", publicKey);
return keys;
}

// Decrypt using RSA public key
private static String decryptMessage(String encryptedText, PublicKey publicKey) throws Exception {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, publicKey);
return new String(cipher.doFinal(Base64.getDecoder().decode(encryptedText)));
}

// Encrypt using RSA private key
private static String encryptMessage(String plainText, PrivateKey privateKey) throws Exception {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
return Base64.getEncoder().encodeToString(cipher.doFinal(plainText.getBytes()));
}

}

Answer 1

I have explained each line in the program please follow program

/*******************************GlobalMembers.java**********************************/

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.util.Base64;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;

// Java 8 example for RSA encryption/decryption.
// Uses strong encryption with 2048 key size.
public class GlobalMembers {

   public static void main(String[] args) throws Exception {
       //declare and save the plain text to string
       String plainText = "Hello World!";

       // Generate public and private keys using RSA
       Map<String, Object> keys = getRSAKeys();//get the keys by calling getRSAKeys method
      
       //get the private key from map
       PrivateKey privateKey = (PrivateKey) keys.get("private");
       //get the public key from map
       PublicKey publicKey = (PublicKey) keys.get("public");

       //get the encyptedText by calling method encyptedMessage by passing plainText and private key
       String encryptedText = encryptMessage(plainText, privateKey);
       //get decryptedText by calling method decryptedMessage by passing encryptedText and public key
       String descryptedText = decryptMessage(encryptedText, publicKey);

       //print input plain text
       System.out.println("input:" + plainText);
       //print encrypted text
       System.out.println("encrypted:" + encryptedText);
       //print decrypted text
       System.out.println("decrypted:" + descryptedText);

   }

   // Get RSA keys. Uses key size of 2048.
   private static Map<String, Object> getRSAKeys() throws Exception {
       /**
       * Creating KeyPair generator object
       * getInstance() method which accepts a String variable representing the required key-generating algorithm
       * and returns a KeyPairGenerator object that generates keys.
       */
       KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
       /*
       * initialize() method is used to initialize the key pair generator.
       * This method accepts an integer value representing the key size.
       */
       keyPairGenerator.initialize(2048);
       /*
       * Generate the pair of keys
       * using the generateKeyPair() method
       */
       KeyPair keyPair = keyPairGenerator.generateKeyPair();
       /*
       * Getting the private key from the key pair
       */
       PrivateKey privateKey = keyPair.getPrivate();
       /*
       * Getting the public key from the key pair
       */
       PublicKey publicKey = keyPair.getPublic();

       /*
       * A Map is used to store the keys String is the information which is String type
       * And The keys are Object type
       */
       Map<String, Object> keys = new HashMap<String, Object>(); //initialize the map
       keys.put("private", privateKey);//store private key in the map by put method
       keys.put("public", publicKey);//store public key in the map
       return keys;
   }

   // Decrypt using RSA public key
   private static String decryptMessage(String encryptedText, PublicKey publicKey) throws Exception {
       //Creating a Cipher by getInstance() method
       Cipher cipher = Cipher.getInstance("RSA");
       //Cipher Mode
       cipher.init(Cipher.DECRYPT_MODE, publicKey);
       //return the encrypted text
       return new String(cipher.doFinal(Base64.getDecoder().decode(encryptedText)));
   }

   // Encrypt using RSA private key
   private static String encryptMessage(String plainText, PrivateKey privateKey) throws Exception {
       //Creating a Cipher by getInstance() method
       Cipher cipher = Cipher.getInstance("RSA");
       //Cipher Mode
       cipher.init(Cipher.ENCRYPT_MODE, privateKey);
       //return the decrypted text
       return Base64.getEncoder().encodeToString(cipher.doFinal(plainText.getBytes()));
   }

}
/*******************output*******************************/

input:Hello World!
encrypted:w3wMlGbKMpVRG01ZdlaQ6FIA+DQBeGcL2f2WYYT/GFBFI/a29/+fRVnf5RjWXmWtyuJsgDSG3arXSW58XnqLcvfZ0uxR9RsyD9s/Itj6bYE8L+3e5vxnZu5Ldp0dOtQ/gsZ6lUyJqfT1iYiVTcBv6gAAv0wx8ctUDvKy9fb8dGLj0ONqiTwO5yiIYXSSSzOzGyM4bQBop40HBsX7UNHAngwuN6z1Wc+/TU3bk8tnxXrrReYM1SJTRyU4HeUFvvPi2UHGVcg/XCMnGAQHuS/kr1MfcP+e8aWpMrTvg2F/Njoy8ykIdGyYY5BIbhZNKUt360SUrqjpbH+DNHAddX14bQ==
decrypted:Hello World!

<terminated> GlobalMembers [Java Application] C:\Program FilesJavaljre1.8.0_131 binjavaw.exe (Apr 11, 2019, 10:31:52 AM) input: Hello World! decrypted:Hello World!

Thanks a lot, Please let me know if you have any problem..............