Visual Cryptography

This applet was written at the chair of Management of InformationSecurity at the University of Regensburg for a project seminar. Goal of this Applet is to demonstrate the wide range and mightiness of the Visiual Cryptography.

So what is Visual Cryptography?

Visual cryptography was introduced by Moni Naor und Adi Shamir in 1994. This new type of cryptographic scheme, which is is perfectly secure, can decode concealed images without any cryptographic computations by the human visual system. For an example take a look at this Applet. For further information on the model see

• Paper by Naor and Shamir presented at EUROCRYPT 94
• Doug Stinson's Visual Cryptography Page

How to get the applet running correctly

Using the applet you might find some strange behaviour in the application. This is due to the mode of operation of the Java Policy. As your machine is running a java applet there are some security restrictions applied for denying access to your local filesystem. If you want to use the applet in all its parts, you can easily call the policytool program in java/bin folder and set up a new policy in {HOME}\.java.policy (for windows users).

Follow these points:

1. Call "policytool" program in "java/bin" folder
2. Click on "Add policy entry" button
3. Click on "Add permission" button
4. In permission box, select "All permission"
5. Click "OK" to go on (after that a new rule is visible in policy entry window)
6. Now click "end" (you could read "codebase(ALL)" in main window)
7. Select File->Save and provide ".java.policy" name
8. Close policytool utility program.

Using the policytool utility program, you can also set a restricted folder for the VCApplet access (refer to sun web site).
Sometimes it is necessary to reload the policy-file. To do so type r in the Java Console.
To set back the basic java security policy, please remove the permission created after the use of the applet.

Alternatively - without using java policytool - create a file named .java.policy with content:
  grant {
     permission java.security.AllPermission;
  };
and place it in your home-directory or download it here.

The Applet

Help

The help file is integrated in the applet. Click within the applet and press F1 to access it easily.

Version History

• 1.1.4 first release with help function
• 1.0 final project seminar