Securing DICOM images through automatic selective encryption

Securing Digital Imaging and Communications in Medicine (DICOM) images are essential to protect the privacy of patients, especially in the era of communications, telemedicine and eHealth/mHealth. This increases the demand for rapid security. Nevertheless, a limited number of research work has been conducted to ensure the security of DICOM images while minimising the processing time. Hence, this thesis introduces a novel selective encryption approach to reduce the processing time and sustain robustness of security. The proposed approach selects regions within medical images automatically in the spatial domain using pixel thresholding segmentation technique, then compresses and encrypts them using different encryption algorithms based on their importance.

The presented approaches in this thesis are developed for multi-frame and single-frame DICOM images. As the medical images of the same modality and the same body part for different patients have the same statistical distribution, it is possible to segment images from the same modality and same body part into Region of Interest (ROI) and Region of Background (ROB) using a pre-defined threshold. In the case of small ROI, an adaptive two-region encryption approach is applied to single and multi-frame DICOM image. In which, the ROB is encrypted using a light encryption algorithm, while the ROI is encrypted using a sophisticated encryption algorithm. For multi-frame DICOM images, additional time saving has been achieved using one segmentation map based on a pre-defined reference frame for all the DIOCM frames. On the other hand, if ROI is very large, i.e. Mammography DICOM images, the ROI is further split into three regions (multi-region) based on potential security threats, using a novel mathematical model that guarantees shorter encryption time in comparison with the Naive encryption approach. After that, each region is compressed using lossless compression approach, and then encrypted using a different encryption algorithm with different key lengths based on its pixels' intensity.

Results from the presented approaches show that processing time is reduced by an average of 54% in comparison with the Naïve encryption approach while maintaining the security of the DICOM images. Further, cryptanalysis metrics are utilised to evaluate the proposed approaches, which indicate good robustness against wide varieties of attacks.