Mathematical Image Analysis Group, Saarland University

Information Security and Cryptography

Motivation

Information security and cryptography play a major role in the digital age. Images as confidential information constitute a special type of messages. On one hand this allows adapted attacks, that cannot be applied to conventional text messages. On the other hand it opens the door to novel cryptographic applications. In both cases a broad knowledge in the area of image processing is of major importance.

Our Contributions

Information Security

Reflecting objects such as tea pots and glasses, but also the user's eye and diffusely reflecting objects such as a user's shirt, can be used to spy on confidential data displayed on a monitor. However, the ability to read this information is often limited by blur. In [1] we show how (non-blind) deconvolution techniques can be used to remove motion blur and out-of-focus blur so that the image quality is drastically improved.

Refection in the eye
Reflections captured in the eye from a distance of 10 meters.

Result with deconvolution
Example of an extremely blurred image (in the eye, from 10 meters) with PSF captured at the same time (left), the extracted PSF (middle), and the result of deconvolution (right).

Steganography

Steganography is the art of hiding the presence of an embedded message (called secret) within a seemingly harmless message (called cover). It can be seen as the complement of cryptography, whose goal is to hide the content of a message. In [2] we demonstrate that one can adapt our diffusion-based image compression techniques such that they become ideally suited for steganographic applications. The resulting method, which we call Stenography with Diffusion Inpainting (SDI), even allows to embed large colour images into small grayscale images. Moreover, our approach is well-suited for uncensoring applications. A web demonstrator for hiding as well as one for censoring is available at http://stego.mia.uni-saarland.de.

Cover image
Stego image, i.e.
cover containing a secret.

Publications

M. Backes, T. Chen, M. Dürmuth, H. Lensch, M. Welk:
Tempest in a teapot: compromising reflections revisited.
Proc. 30th IEEE Symposium on Security and Privacy, Oakland, USA, 315–327. IEEE Computer Society, 2009.

M. Mainberger, C. Schmaltz, M. Berg, J. Weickert, M. Backes:
Diffusion-based image compression in steganography.
In G. Bebis, R. Boyle, B. Parvin, D. Koracin, C. Fowlkes, S. Wang, M.-H. Choi, S. Mantler, J. Schulze, D. Acevedo, K. Mueller, M. Papka (Eds.): Advances in Visual Computing, Part II. Lecture Notes in Computer Science, Vol. 7432, 219-228, Springer, Berlin, 2012.