Posts for Tag: java

Java in Firefox after v52.0 (Checkpoint VPN)

Firefox has changed a few things in its plugin infrastructure and that means Java will no longer work properly after version 52.0 (especially if you are using Checkpoint VPN to access work).

Fortunately one can always install older versions, present here:

Also, be sure to disable automatic updates in the settings to prevent the browser from updating itself (default).

Bonus step (if you are on the mac configuring Checkpoint):

The newest OSX has a safety feature called SIP (System Integration Protection) that will prevent the checkpoint from installing the required files in the system. To work around this, you need to disable it temporarily:

  • Boot into recovery mode (restart and press Command + R on hearing the beep)
  • Open the terminal and type:
  • csrutil disable
  • Reboot
  • Access the vpn and the snx_extender installation step will work.
  • Go back into recovery and enable SIP again:
  • csrutil enable

Happy VPN'ing

AES encryption in Ruby and Decryption in Java

This one is precious, as it took me a long time to figure out. As a side-note, Java apparently only supports 128bit AES.

Here's the Ruby code:

def encrypt(string, pwd)
    salt = OpenSSL::Random.random_bytes(16)

    # prepare cipher for encryption
    e ='AES-128-CBC')

    # next, generate a PKCS5-based string for your key + initialization vector
    key_iv = OpenSSL::PKCS5.pbkdf2_hmac_sha1(pwd, salt, 1024, e.key_len+e.iv_len)
    key = key_iv[0, e.key_len]
    iv  = key_iv[e.key_len, e.iv_len]

    # now set the key and iv for the encrypting cipher
    e.key = key
    e.iv  = iv

    # encrypt the data!
    encrypted = '' << e.update(string) <<
    [encrypted, iv, salt].map {|v| ::Base64.strict_encode64(v)}.join("--")   

And the Java part:

public static String decrypt(String encrypted, String pwd) throws Exception {

        String[] parts = encrypted.split("--");
        if (parts.length != 3) return null;

        byte[] encryptedData = Base64.decodeBase64(parts[0]);
        byte[] iv = Base64.decodeBase64(parts[1]);
        byte[] salt = Base64.decodeBase64(parts[2]);

        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
        KeySpec spec = new PBEKeySpec(pwd.toCharArray(), salt, 1024, 128);
        SecretKey tmp = factory.generateSecret(spec);
        SecretKey aesKey = new SecretKeySpec(tmp.getEncoded(), "AES");

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, aesKey, new IvParameterSpec(iv));

        byte[] result = cipher.doFinal(encryptedData);
        return new String(result, "UTF-8");

'OSX Mavericks "You need a Java 6 runtime to run X" error dialog fix'

Ok, so here's the deal: If you upgrade to [OSX Mavericks](, only had JAVA 7 installed, and try to run anything that requires JAVA you will probably get a nice dialog like this one:

All my attempts to make Mavericks use JAVA 7 instead have failed so i tried the next best thing: Install JAVA 6. Since you can't find JAVA 6 for Mac at the [Oracle]( site, you'll have to install it from here: [Java for OS X 2013-004](

After installing you'll end up with this following structure at the "/System/Library/Frameworks/JavaVM.framework/Versions" folder:

drwxr-xr-x 11 root wheel 374 29 Ago 14: lrwxr-xr-x 1 root wheel 10 29 Ago 14:58 1.4@ -> CurrentJDK lrwxr-xr-x 1 root wheel 10 29 Ago 14:58 1.4.2@ -> CurrentJDK lrwxr-xr-x 1 root wheel 10 29 Ago 14:58 1.5@ -> CurrentJDK lrwxr-xr-x 1 root wheel 10 29 Ago 14:58 1.5.0@ -> CurrentJDK lrwxr-xr-x 1 root wheel 10 29 Ago 14:58 1.6@ -> CurrentJDK lrwxr-xr-x 1 root wheel 10 29 Ago 14:58 1.6.0@ -> CurrentJDK drwxr-xr-x 7 root wheel 238 29 Ago 14:58 A/ lrwxr-xr-x 1 root wheel 1 29 Ago 14:58 Current@ -> A lrwxr-xr-x 1 root wheel 59 29 Ago 14:58 CurrentJDK@ -> /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents

So you might want to fix the path to the current JDK, so that you keep using the JDK 7 by default (Eclipse users, you know what i mean ;)):

$ sudo rm CurrentJDK $ sudo ln -s /Library/Java/ $ sudo ln -s /Library/Java/JavaVirtualMachines/jdk1.7.0_25.jdk/Contents CurrentJDK

Another thing you might need to change is the JAVA_HOME environment variable but, since that depends on whatever shell you use, [Google it]( ;)

Finally, verify that you are still using JAVA 7 by default:

$ javac -version javac 1.7.0_25 $ java -version java version "1.7.0_25"

Have fun.

JAVA vertical gradient background panel

Recently i had to create a gradient background for one of the panels in our [POS application](, so i though i'd share the code.

You need to pass the top and bottom colors of the gradient and also make sure that any panels inside this one are transparent (i.e. setOpaque(false)), otherwise they will paint above it.

import java.awt.Color; import java.awt.GradientPaint; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.RenderingHints;

import javax.swing.JPanel;

public class VerticalGradientBackgroundPanel extends JPanel {

private Color topColor; private Color bottomColor;

public VerticalGradientBackgroundPanel(Color topColor, Color bottomColor) {

this.topColor = topColor; this.bottomColor = bottomColor; }

@Override protected void paintComponent(Graphics grphcs) {


Graphics2D g2d = (Graphics2D) grphcs;

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); GradientPaint gp = new GradientPaint(0, 0, topColor, 0, getHeight(), bottomColor); g2d.setPaint(gp); g2d.fillRect(0, 0, getWidth(), getHeight()); } }

JAVA JScrollPane change scroll amount/increment