RSA Encryption/Decryption - Part 2

My previous post on RSA details about basics of RSA and how to generate public and private key in java.

Encryption in Java

         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;
 }

Decryption in Java

         public static String decrypt(byte[] text, PrivateKey key) {
  byte[] decryptedText = 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);
   decryptedText = cipher.doFinal(text);

  } catch (Exception ex) {
   ex.printStackTrace();
  }

  return new String(decryptedText);
 }

RSA Encryption/Decryption - Part 1

What is Cryptography?

Cryptography is the practice or techniques for securing a communication in the presence of others. It is about constructing and analyzing protocols that overcome the influence of adversaries and are related to various aspects in information security such as data confidentiality, data integrity, authentication.

What is Encryption?

Encryption is one of the ways to achieve data security by translation of data into secret code or unreadable format called cipher text.

What is Decryption?

Decryption is the reverse of encryption that is converting cipher text to its original message, i.e. plain or readable text.

What is RSA?

RSA is one of the widely used public key cryptography for secure data communication. RSA stands for Ron Rivest, Adi Shamir and Leonard Adleman, who first publicly described it in 1978. Public key cryptohraphy is also called Asymmetric cryptography which requires two separate keys, one which is private key (secret key) and another which is public key. the public key is used to encrypt text while private key is used to decrypt text.

How to generate public/private key in java?

public static void generateKey(String private_key, String public_key) {
  try {
   final KeyPairGenerator keyGen = KeyPairGenerator
     .getInstance(ALGORITHM);
   keyGen.initialize(512);
   final KeyPair key = keyGen.generateKeyPair();

   File privateKeyFile = new File(private_key);
   File publicKeyFile = new File(public_key);

   // 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();
  }

 }

To call

generateKey("c:/rsa/key/public.key", "c:/rsa/key/private.key");

My next post on RSA details about how to encrypt and decrypt in java using  public and private key generated above.

Liferay: Custom 404 Page for plugins

Liferay portal runs and is configured as ROOT application with in tomcat sever.
By default, if tried to request a plugin in Liferay (say we have a theme plugin named as "error-theme"), a 404 Error is raised and the user is served Tomcat's default 404 error page as below:

To make your 404 page a bit more presentable, provide the user with a link back into your site, as well as hide the Tomcat version in use, you can easily add a custom 404 error page.

Step 1:

Create a jsp name it 404.jsp, with below content:

The requested resource is not available. Please provide the correct URL or try again later.
<br/>
<a href="#" onclick="javascript:history.go(-1);">Go back to main site.</a>

Step 2:

Now create a new directory as error-theme/docroot/errors in Lifeay IDE and copy the above created 404.jsp to it.

Step 3:

Last step is to add the below code to the web deployment descriptor (web.xml) of the plugin:

         <error-page>
  <error-code>404</error-code>
  <location>/errors/404.jsp</location>
 </error-page>

Now, when someone goes to the plugin link that does not exist, they get the custom 404 page we created.

JQuery : Declare a function

Method 1: The Javascript way

The simple way to declare a  function in javascript:

function callMe (count) {
     return (count+5);
}

console.log(callMe(13));
//output: 18

Disadvantage: If you wanted a quick function to test something then maybe that’s the only occasion you would use this. It’s not good coding and doesn’t promote code reuse.

Method 2: Creating your JQuery function

The simple way to declare a  function in javascript:

<div id="mydiv">i am here</div>

jQuery.fn.extend({
    mytext: function () {
        var text = $(this).text();
        var mytexts = '';
        var toggle = true; //lower/uppper toggle
            $.each(text, function(i, nome) {
                mytexts += (toggle) ? nome.toUpperCase() : nome.toLowerCase();
                toggle = (toggle) ? false : true;
            });
    return mytexts;
    }
});

console.log($('#mydiv').zigzag());
//output: #1 i aM HeRe

//chained example
console.log($('#mydiv').zigzag().toLowerCase());
//output: #1 i am here

Method 1: Functions in custom namespaces

If your writing functions in a custom namespace you must declare them in this way. Extra functions can be added to the namespace you just need to add a comma after each one (except the last one!).

JQUERY4U = {
    callme: function(count) {
        return (count + 5);
    }
}
//function call
JQUERY4U.callme(13);

Reference post: Full credit goes to the original post, which made the topic so easy to understand (visit for more details).

Liferay 6: Monitoring tomcat.

The Liferay tomcat bundle is available for download on http://www.liferay.com/downloads/liferay-portal/available-releases and instant use. It ships pre-configured with hypersonic database and you can switch to mysql, oracle, etc for permanent solutions.

When moving your site or solution to production server there is always uncertainty on how much the load will be coming at peak time, how many request the tomcat will be able to server with Liferay. Although the Apache tomcat comes with tomcat-manager application that allows you to monitor all the resources via JMX beans. but since this have been removed in Liferay-tomcat bundle thus it is hard to monitor the resources and threads the tomcat server is consuming. Thus to over come this shortcoming, below are the steps to enable the monitoring in the tomcat:

Server Details
Liferay: 6.1.2 GA2 Enterprise
Tomcat Bundle: 7.0.27
Java 6

Step 1:
Stop the running Liferay tomcat server and clean the temp and work folder.

Step 2:
Download the vanilla apache tomcat server of the same version and unzip it at some temporary location.

Step 3:
Copy host-manager and manager application <tomcat>/webapps directory to liferay installation at <liferay-tomcat-bundle>/tomcat-7.0.27/webapps

Step 4:
Create a manager.xml file at location <liferay-tomcat-bundle>/tomcat-7.0.27/conf/Catalina/localhost.
And the following content to it and save it

<Context antiResourceLocking="false" privileged="true" useHttpOnly="true">
 
 </Context>

Step 5:
Now open file <liferay-tomcat-bundle>/tomcat-7.0.27/conf/tomcat-users.xml in edit mode. And the below content inside the tag <tomcat-users>.

<tomcat-users>
...

  <role rolename="tomcat"/>
  <role rolename="manager-gui"/>
  <role rolename="standard"/>
  <role rolename="manager"/>
  <role rolename="admin"/>
  <user username="tomcat" password="tomcat" roles="manager,admin,standard,manager-gui,tomcat"/>

...
</tomcat-users>

Step 6:

Now restart the tomcat server and go to the URL: http://localhost:8080/manager/html and you will be prompted for username and password which should be the same as defined above.

And now you can monitor the tomcat resources and can tune them accordingly.