Andreas Pommer

Selective encryption of wavelet-packet encoded image data: efficiency and security

Abstract.Selective encryption provides the ability to strike a balance between security and processing demands, e.g., in mobile clients. Image encoding using wavelets, and especially wavelet packets, can be used for efficient selective encryption. We will show how two such methods work and discuss their advantages and disadvantages in terms of security and speed.

Confidential storage and transmission of medical image data

We discuss computationally efficient techniques for confidential storage and transmission of medical image data. Two types of partial encryption techniques based on AES are proposed. The first encrypts a subset of bitplanes of plain image data whereas the second encrypts parts of the JPEG2000 bitstream. We find that encrypting between 20% and 50% of the visual data is sufficient to provide high confidentiality.

Wavelet packet methods for multimedia compression and encryption

We introduce a selective encryption scheme for visual data based on the wavelet packet representation where the structure of a randomly chosen non-stationary multi-resolution analyses (NSMRA) is encrypted only. Whereas the rate-distortion performance of the entire scheme is on an acceptable level we describe a heuristic to break the proposed scheme in linear time.

Are parameterised biorthogonal wavelet filters suited (better) for selective encryption

Selective encryption is used to encrypt parts of a bitstream, in our case images which are compressed by a wavelet based method. One approach is to keep the filter secret which is used for the transformation. Parameterised wavelet filters can be used to generate a large keyspace, however, in the case of orthogonal filters obtained by a variant of Pollens factorisation it turns out that different parameters yield filters with very different quality and in particular worse quality as compared to the standard biorthogonal filters usually used for compression. To eventually overcome these limitations, we consider parametrisations of biorthogonal filters in this work. We discuss methods to create such filters, and show their properties regarding compression and encryption.

Fractal Video Compression on Shared Memory Systems

Fractal image compression is known to be very demanding with respect to CPU-power, and demands are higher again for fractal video compression. Methods to speed up the encoding process can be divided into two groups: one contains sequential speedup-methods like classification, transformation into other search spaces, . . .The other possibility is the use of parallel systems. Here we like to show the possibilities and experiences with shared memory MIMD machines.

Lightweight protection of visual data using high-dimensional wavelet parametrization

A lightweight encryption scheme for visual data based on wavelet filter parametrization is discussed. Being a special variant of header encryption, the technique has an extremely low computational demand. Security assessement of low-dimensional parametrizations schemes show severe weaknesses. We show that using high-dimensional parametrizations the scheme may be employed in applications requiring a medium security level.

Fractal motion compensation

In this work we apply techniques from classical fractal still-image coding to block-matching motion compensation algorithms for digital video compression. Especially the method of adapting the gray-values in image blocks of the current frame to those in blocks of the reference-frame shows promising performance.