Selective encryption of JPEG files

figure tablelands.jpg figure tablelands-user1-user2.jpg figure tablelands-locally.jpg
Original image Selective encryption Selective encryption of some parts only

Principle

JPEG uses the DCT transform to compress images. As described in [1], it is possible to encrypt parts of the JPEG bitstream and guarantee the following properties:
[Visual acceptance] Part of information may be visible but the encrypted image should look noisy.
[Selective encryption] Encryption occurs after compression and leaves parts of the bitstream unencrypted.
[Constant bit rate] Encryption should preserve the size of the bitstream.
[Bitstream compliance] The encryption step should produce a compliant bitstream according to the chosen format definition.
The process is shown in Figure 1↓.
figure encryption-process.png
Figure 1 Selective encryption of a JPEG image.
Here follows an example.
figure ULg.jpg figure ULg-encrypted.jpg
Original image Encrypted image
For the same principle applied to videos, follow this link.

Software description

Please contact Mr Van Droogenbroeck if you are interested in the software. We can provide both a program (for Windows or Linux) and the full source code. Here are the specifications of the software:
  1. Programming language: standard C (compiled with gcc).
  2. Real time encryption and decryption.
  3. External dependencies: Intel® Integrated Performance Primitive.
  4. Possibility to encrypt only parts of the image (see [2] and right-hand side top illustration).
  5. Cascading of encryption (over-encryption) is possible and reversible.

References

[1] M. Van Droogenbroeck, R. Benedet. Techniques for a selective encryption of uncompressed and compressed images. Advances Concepts for Intelligent Vision Systems (ACIVS):90-97, 2002. URL http://www.telecom.ulg.ac.be/publi/publications/mvd/acivs2002mvd/index.html.

[2] M. Van Droogenbroeck. Partial encryption of images for real-time applications. Fourth IEEE Signal Processing Symposium:11-15, 2004. URL http://www.telecom.ulg.ac.be/publi/publications/mvd/sps-2004/index.html. Invited presentation.