De-identi cation through post-compression region of interest...

De-identification through post-compressionregion of interest encryption

EU COST Action IC1206 MC&WG meeting, Valletta

Andreas Unterweger1

Salzburg University of Applied Sciences2

Puch/Hallein, [email protected]

November 2, 2015

1Results are from joint work with Jan De Cock, Dominik Engel, Heinz Hofbauer, Andreas Uhl and Kevin Van Ryckegem.2All of the presented work has been done at the University of Salzburg, Salzburg, Austria.

Andreas Unterweger De-id. through post-compr. RoI encryption November 2, 2015 1 / 15

mailto:[email protected]

Region of Interest Encryption

Encryption of identifying picture region(s), e.g., faces

⇒ Reversible de-identification

Decryption for re-identification, e.g., by law enforcement


The meaning of “post-compression”

Pre-Compression

In-Compression

Post-Compression


Problem statement

In the literature: Mostly pre- and in-compression approaches

Easier to implementFaster for uncompressed input data

In practice: Compressed data

Surveillance videos (JPEG, H.264/AVC and SVC)⇒ How to encrypt without transcoding?


Results: JPEG I

Length-preserving bit-stream-based JPEG encryption3

Swapping of AC Huffman code wordsAdditional AC coefficient encryption (larger key space)Can be limited trivially to regions of interest

3A. Unterweger and A. Uhl. Length-preserving Bit-stream-based JPEG Encryption. In MM&Sec’12: Proceedings of the 14thACM Multimedia and Security Workshop, pages 85–89. ACM, Sept. 2012


Results: JPEG I

Length-preserving bit-stream-based JPEG encryption3

3A. Unterweger and A. Uhl. Length-preserving Bit-stream-based JPEG Encryption. In MM&Sec’12: Proceedings of the 14thACM Multimedia and Security Workshop, pages 85–89. ACM, Sept. 2012


Results: JPEG II

Real-time JPEG encryption4

C implementation of bit-stream-based JPEG encryptionReal-time encryption in VGA resolution

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Du

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JPEG quality [%]

4S. Auer, A. Bliem, D. Engel, A. Uhl, and A. Unterweger. Bitstream-Based JPEG Encryption in Real-time. InternationalJournal of Digital Crime and Forensics, 5(3):1–14, 2013


Results: JPEG III

Extended JPEG encryption5

Extension of C implementation by DC coefficient encryptionCorrection at borders of regions of interest necessary

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foreman (CIF)akiyo (CIF)crew (CIF)hall (CIF)ice (4CIF)

vidyo1 (720p)

5A. Unterweger, K. Van Ryckegem, D. Engel, and A. Uhl. Building a Post-Compression Region-of-Interest EncryptionFramework for Existing Video Surveillance Systems – Challenges, obstacles and practical concerns. Multimedia Systems, 2015.accepted


Results: JPEG III

Extended JPEG encryption5



Results: H.264/AVC I

H.264/AVC encryption with drift minimization6

(Partial) drift compensation at the borders of the regions of interestIncrease of data rate by max. 3% through compensationReduction of processing time by 45% (compared to transcoding)

RoI macroblocks

Macroblocks

depending on RoI

Error accumulation

Error compensation

6A. Unterweger, J. De Cock, and A. Uhl. Bit-Stream-Based Encryption for Regions of Interest in H.264 Videos With DriftMinimization. Technical report, University of Salzburg, Salzburg, 2015. submitted


Results: H.264/AVC I

H.264/AVC encryption with drift minimization6

6A. Unterweger, J. De Cock, and A. Uhl. Bit-Stream-Based Encryption for Regions of Interest in H.264 Videos With DriftMinimization. Technical report, University of Salzburg, Salzburg, 2015. submitted


Results: H.264/AVC II

Slice groups to avoid drift7

Definition of slice group borders around regions of interest requiredAvoids spatial, but not temporal driftIncrease of data rate with quality (approx. 5% at medium quality)

7A. Unterweger and A. Uhl. Slice groups for post-compression region of interest encryption in H.264/AVC and its scalableextension. Signal Processing: Image Communication, 29(10):1158–1170, November 2014


Results: SVC

Slice groups to avoid drift8

No slice groups allowed in base layer ⇒ Replaced by all-grey layerAdditionally avoids inter-layer drift through constrained ILP

Enh. layer

Base layer

8A. Unterweger and A. Uhl. Slice Groups for Post-Compression Region of Interest Encryption in SVC. In IH&MMSec’14:Proceedings of the 2014 ACM Information Hiding and Multimedia Security Workshop, pages 15–22, Salzburg, Austria, June2014. ACM


Other results I

Signaling of regions of interest9

Coding of coordinates and sizes of regions of interest for decryptionDifferent new types of signaling in JPEG/JFIF files

9D. Engel, A. Uhl, and A. Unterweger. Region of Interest Signalling for Encrypted JPEG Images. In IH&MMSec’13:Proceedings of the 1st ACM Workshop on Information Hiding and Multimedia Security, pages 165–174. ACM, June 2013


Other results II

Framework for surveillance systems10

Combined (real-time) JPEG encryption and signalingModular implementation with face detection and decryptionCan be used to extend existing surveillance systems



Other results II


Assessment of face detection algorithms for region of interest detectionFace detection requires 99% of the total processing timeState-of-the-art face detection algorithms are not good enough

Sequence Overhead [%] Precision [%] Recall [%]foreman (CIF) 0.137 50.3 82.4akiyo (CIF) 0.242 53.2 99.5crew (CIF) 0.353 33.2 53.3hall (CIF) 0.102 62.3 28.3ice (4CIF) 0.083 36.1 20.7vidyo1 (720p) 0.163 18.0 70.6



Other results II


Subjective evaluation of different encryption methods (find 1 face in 5)Some people may be identified despite encryption

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Other results III

Security analysis of pure AC coefficient sign encryption11

Widely used, easy to implement, but hardly ever analyzed w.r.t. securityKey space is often huge, but not a meaningful measureAssessment of JPEG and H.265/HEVC with replacement attackDCT coefficient sign encryption not suitable for confidential encryption

11H. Hofbauer, A. Unterweger, and A. Uhl. Encrypting Only AC Coefficient Signs considered Harmful. In Proceedings of theIEEE International Conference on Image Processing 2015 (ICIP’15). IEEE, Sept. 2015. accepted


Conclusion

Advantages of post-compression region of interest encryption

No need for transcoding (saves time)Easier to integrate into existing (compression-based) systems

Disadvantages of post-compression region of interest encryption

Higher design and implementation complexity(More) Difficult to avoid drift

Biggest open issue: Temporal drift in H.264/AVC and SVC


Thank you for your attention!

Questions?

All papers are available at http://www.wavelab.at/member-aunterweger.shtml


http://www.wavelab.at/member-aunterweger.shtml

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