Alexander Christ, Universität Tübingen, 2008

Visual Cryptography

Visual cryptography is used to encrypt images. On the canvas below you can draw pictures or write text. Meanwhile two secret images will be created. Moved over another, they show the canvas' content. All images can be saved or printed on transparencies.

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Seminar Paper

This application was written as a seminar project. It aims to demonstrate visual cryptography using AJAX-Technology. Technical and theoretical details were documented in a seminar paper which is available here.


This application can be used in playful or educational ways. But it is also useful in "real world" scenarios: Imagine an employee who is moved to a foreign country. He will need new passwords on a regular basis in order to access his firm's data. Therefor 20 secret images will be created before the voyage starts. For the employee they will be printed on transparencies. The employer instead saves them electronically on his computer. To send a new password the employer has to load one of the secret images, write the password on the canvas and save the complementary image as PDF. This file will be send to the employee who can print it on paper. When the paper is overlayed with the corresponding transparency the password can be encrypted. The e-mail can be intercepted, since one secret image alone does not reveal any information about the encrypted message.