How do I get cryptographic security providers?

By I Wayan Saryada in Security 0 Comment 
package org.kodejava.security;

import java.security.Provider;
import java.security.Security;
import java.util.Set;
import java.util.HashSet;

public class SecurityProvider {
    public static void main(String[] args) {
        // Create a set so that we can have a unique results.
        Set<String> results = new HashSet<>();

        // Returns an array containing all the installed providers.
        Provider[] providers = Security.getProviders();

        for (Provider provider : providers) {

            // Get provider's property keys
            Set<Object> keys = provider.keySet();
            for (Object key : keys) {
                String data = (String) key;
                data = data.split(" ")[0];

                // Service type started by the "Alg.Alias" string
                if (data.startsWith("Alg.Alias")) {
                    data = data.substring(10);
                }

                data = data.substring(0, data.indexOf('.'));
                results.add(data);
            }
        }

        for (Object object : results) {
            System.out.println("Service Type = " + object);
        }
    }
}

The example result of our code:

Service Type = Policy
Service Type = Configuration
Service Type = AlgorithmParameterGenerator
Service Type = TransformService
Service Type = CertificateFactory
Service Type = KeyInfoFactory
Service Type = CertPathBuilder
Service Type = MessageDigest
Service Type = KeyAgreement
Service Type = SecretKeyFactory
Service Type = KeyGenerator
Service Type = KeyFactory
Service Type = XMLSignatureFactory
Service Type = SaslServerFactory
Service Type = TerminalFactory
Service Type = SecureRandom
Service Type = SaslClientFactory
Service Type = KeyPairGenerator
Service Type = SSLContext
Service Type = KeyStore
Service Type = Mac
Service Type = Provider
Service Type = KeyManagerFactory
Service Type = CertPathValidator
Service Type = Signature
Service Type = TrustManagerFactory
Service Type = Cipher
Service Type = CertStore
Service Type = GssApiMechanism
Service Type = AlgorithmParameters

How do I decrypt an object with DES?

By I Wayan Saryada in Core API, Cryptography 0 Comment

On the previous example How do I encrypt an object with DES? we encrypt an object. In this example we will decrypt the stored object.

package org.kodejava.crypto;

import java.io.*;

import javax.crypto.SecretKey;
import javax.crypto.Cipher;
import javax.crypto.SealedObject;

public class ObjectDecrypt {
    public static void main(String[] args) throws Exception {
        // Read the previously stored SecretKey.
        SecretKey key = (SecretKey) readFromFile("secretkey.dat");

        // Read the SealedObject
        SealedObject sealedObject = (SealedObject) readFromFile("sealed.dat");

        // Preparing Cipher object from decryption.
        if (sealedObject != null) {
            String algorithmName = sealedObject.getAlgorithm();

            Cipher cipher = Cipher.getInstance(algorithmName);
            cipher.init(Cipher.DECRYPT_MODE, key);

            String text = (String) sealedObject.getObject(cipher);
            System.out.println("Text = " + text);
        }
    }

    // Method for reading object stored in a file.
    private static Object readFromFile(String filename) {
        try (FileInputStream fis = new FileInputStream(filename);
             ObjectInputStream ois = new ObjectInputStream(fis)) {

            return ois.readObject();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

How do I encrypt an object with DES?

By I Wayan Saryada in Core API, Cryptography 0 Comment

This example demonstrate encrypting an object using DES algorithm. After the object was encrypted we store it in a file which will be decrypted in the next example here How do I decrypt an object with DES.

package org.kodejava.crypto;

import java.io.*;

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

public class ObjectEncrypt {
    public static void main(String[] args) throws Exception {
        // Generating a temporary key and store it in a file.
        SecretKey key = KeyGenerator.getInstance("DES").generateKey();
        writeToFile("secretkey.dat", key);

        // Preparing Cipher object for encryption.
        Cipher cipher = Cipher.getInstance("DES");
        cipher.init(Cipher.ENCRYPT_MODE, key);

        // Here we seal (encrypt) a simple string message (a string object).
        SealedObject sealedObject = new SealedObject("THIS IS A SECRET MESSAGE!", cipher);

        // Write the object out as a binary file.
        writeToFile("sealed.dat", sealedObject);
    }

    // Store object in a file for future use.
    private static void writeToFile(String filename, Object object) throws Exception {
        try (FileOutputStream fos = new FileOutputStream(filename);
             ObjectOutputStream oos = new ObjectOutputStream(fos)) {

            oos.writeObject(object);
        }
    }
}

How do I determine whether a string is a palindrome?

By I Wayan Saryada in Core API, Lang Package 0 Comment

This code checks a string to determine if it is a palindrome or not. A palindrome is a word, phrase, or sequence that reads the same backward as forward.

package org.kodejava.lang;

public class PalindromeChecker {

    public static void main(String[] args) {
        String text = "Sator Arepo Tenet Opera Rotas";

        PalindromeChecker checker = new PalindromeChecker();
        System.out.println("Is palindrome = " + checker.isPalindrome(text));
    }

    /**
     * This method checks the string for palindrome. We use StringBuilder to
     * reverse the original string.
     *
     * @param text a text to be checked for palindrome.
     * @return <code>true</code> if a text is palindrome.
     */
    private boolean isPalindrome(String text) {
        System.out.println("Original text = " + text);

        String reverse = new StringBuilder(text).reverse().toString();
        System.out.println("Reverse text  = " + reverse);

        // Compare the original text with the reverse one and ignoring its case
        return text.equalsIgnoreCase(reverse);
    }
}

How do I create a thread by implementing Runnable interface?

By I Wayan Saryada in Core API, Lang Package 0 Comment

Here is the second way for creating a thread. We create an object that implements the java.lang.Runnable interface. For another example see How do I create a thread by extending Thread class?.

package org.kodejava.lang;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class TimeThread implements Runnable {
    private final DateFormat df = new SimpleDateFormat("hh:mm:ss");

    // The run() method will be invoked when the thread of this runnable object
    // is started.
    @Override
    public void run() {
        while (true) {
            Calendar calendar = Calendar.getInstance();
            System.out.format("Now is: %s.%n", df.format(calendar.getTime()));

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        TimeThread time = new TimeThread();

        Thread thread = new Thread(time);
        thread.start();
    }
}

An example result of this code are:

Now is: 07:18:39.
Now is: 07:18:40.
Now is: 07:18:41.
Now is: 07:18:42.
Now is: 07:18:43.