Frédéric Dufaux and Touradj Ebrahimi

           Presents by Kobi Magnezi
Abstract
— Problem:
  Preserving privacy in video surveillance
— Solution:
  Scrambling regions of interest (ROI) in a vid...
Abstract
— Real life:
   — MPEG-4
   — Motion JPEG 2000
— Results:
   — Conceal information in ROI in the scene while
    ...
Motivation
— Video surveillance systems are becoming ubiquitous.
   — Strategic places
   — Airports
   — Banks
   — Publi...
George Orwell
Big brother: “While tens of millions in government
  funding have been spent on research improving video
  s...
Architecture

Wireless




           Wired
Architecture
Architecture

                      ROI
     Scramble




                Compress



                            •Face de...
5 Previous approaches addressed
privacy in video surveillance
Blinkering Surveillance: Enabling
Video Privacy through Computer Vision. IBM Technical
— “Just enoughquot; of the video st...
Blinkering Surveillance: Enabling
Video Privacy through Computer Vision. IBM Technical
— Approach
   — OO representation o...
“The networked
sensor tapestry (NeST): a privacy enhanced software
architecture for interactive analysis of data in video-...
“The networked
sensor tapestry (NeST): a privacy enhanced software
architecture for interactive analysis of data in video-...
Preserving Privacy by De-identifying Facial Images
— Algorithm to protect the privacy by de-identifying
  faces
— Old appr...
Preserving Privacy by De-identifying Facial Images
New approach - k-Same
limits the ability of face recognition software.
...
Privacy through Invertible Cryptographic Obscuration
— Scene distortion via cryptography
— Encryption techniques to improv...
Video surveillance using JPEG 2000
— JPEG 2000 compression
— Events detection and ROI identification
— Compressed video st...
JPWL / JPSec Schema
Previous approaches with JPEG
— The process
   — Identify ROI (people, privacy-sensitive info)
   — ROIs à Code-blocks
   ...
How we’ll make it better?
— We want that
   — Scene remains understandable
   — The people are unidentifiable.
— Security
...
How we’ll make it better?
— Output: single protected code-stream to all clients
  — No private key à distorted version of ...
Public/Private key encryption
Why Compress/Encode
  Video Source                     Output Data Rate[Kbits/sec]
  Quarter VGA @20 frames/sec       36 8...
MPEG-4
— Based on a motion compensation
— Block-based DCT
— Compression




                    Predicted frames
         ...
Four 8x8
              Blocks for DCT




   16x16
MacroBlocks
black with lot of
                                                              change in
                                ...
DCT
                 cosine function: horizontal, diagonal
                 and vertical frequencies




                 ...
Human visual system
                          experiments
                      standard quantization
                    ...
Quality factor of 75
Quality factor of 20
Quality factor of 5
Quality factor of 3
Entropy Encoder (Compress…)
— Variable length Coding
     Huffman Coding
     or others…
Huffman Coding
— The symbol with the highest probability is assigned
  the shortest code and vice versa.
— Code words leng...
Huffman Coding
Video Scrambling
Earlier works                        Our approach
— Traditional cryptographic          — Bit scrambling
 ...
So when we scrambling?
Before                                        After
Perform scrambling in the original            A...
Transform-domain Scrambling
— Frames transform using an energy compaction
  transform: DCT, DWT
— The resulting coefficien...
MPEG-4 & Scrambling
— Effectively applied
  on the quantized
  DCT coefficients,
  and outside of the
  motion
  compensat...
The scrambling recipe
— What can be scrambled?
  — In general, DC coefficients are strongly correlated and
    are therefo...
The scrambling recipe
— So what can be done?
   — All DC coefficients of the blocks corresponding to the
     ROIs are scr...
The scrambling recipe
— The shape of the scrambled region is restricted to
  match the 8x8 DCT blocks boundaries.
— Level ...
Drifts…
— Unauthorized decoder (not capable of unscrambling) will
  use a different motion compensation loop than an
  aut...
How to avoid it?
— Scrambled MB in the reference frame, are always
  INTRA coded.
— Prevents the drift in motion compensat...
Encryption
— PRNG initialized by a seed
   — SHA1PRNG with 64bit seed
   — Increase security à Multiple seed can be used
—...
Complexity?
— Flipping sings of selected coefficients
Scrambling
— Effectively applied after the DWT and quantization,
  and before the arithmetic coder
De-Srambling
— The process is fully reversible. At the decoder,
  authorized users have merely to perform the exact
  inve...
Looks familiar?
— Similar approach as proposed for MPEG-4
— Quantized wavelet coefficients are scrambled by
  pseudo rando...
Slide 56

                 ????         KM2
             bandwith
Kobi Magnezi, 10/06/2009
Goodies of JPEG2000
— The shape of the ROIs
  — Embedded ROI mechanism of JPEG 2000.
— Leveraging standard JPEG security (...
Varying scrambling strength for
MPEG-4
Varying scrambling strength for
Motion HPEG 2000
Coding
efficiency
MPEG-4

     Less than 10%
    bitrate increases
Coding
efficiency
Motion
JPEG2000

   Approximately 10%
    bitrate increases
Security Strength
— Brute-force attack
   — tries all combinations reversing the signs of all non-zero AC
     coefficient...
something to think about…
Eagle Eye
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
Scrambling For Video Surveillance
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Scrambling For Video Surveillance

  1. 1. Frédéric Dufaux and Touradj Ebrahimi Presents by Kobi Magnezi
  2. 2. Abstract — Problem: Preserving privacy in video surveillance — Solution: Scrambling regions of interest (ROI) in a video sequence. — Implementation: efficient solution based on transform-domain scrambling
  3. 3. Abstract — Real life: — MPEG-4 — Motion JPEG 2000 — Results: — Conceal information in ROI in the scene while providing with a good level of security — Scrambling is flexible – distortion can be adjusted — Small impact on coding performance and negligible computational complexity increase.
  4. 4. Motivation — Video surveillance systems are becoming ubiquitous. — Strategic places — Airports — Banks — Public transportation — Busy city centers. — Increase security but fear the loss of privacy — à slowing down the deployment of video surveillance.
  5. 5. George Orwell Big brother: “While tens of millions in government funding have been spent on research improving video surveillance, virtually none has been invested in technologies to enhance privacy or effectively balance privacy and security”
  6. 6. Architecture Wireless Wired
  7. 7. Architecture
  8. 8. Architecture ROI Scramble Compress •Face detections •Change Detection •Tracking •Skin detection Privacy Video •Object segmentation & tracking •Combination
  9. 9. 5 Previous approaches addressed privacy in video surveillance
  10. 10. Blinkering Surveillance: Enabling Video Privacy through Computer Vision. IBM Technical — “Just enoughquot; of the video stream — OO — PrivacyCam
  11. 11. Blinkering Surveillance: Enabling Video Privacy through Computer Vision. IBM Technical — Approach — OO representation of the scene — Re-render frames based on ACL — Technology — Privacy console that manages different versions of the video data based on ACL. — Privacy Cam - smart camera produces a video stream with the privacy-intrusive information already removed.
  12. 12. “The networked sensor tapestry (NeST): a privacy enhanced software architecture for interactive analysis of data in video-sensor networks — Networked Sensor Tapestry (NeST) Test-bed under development — Secure sharing — Capture — Distributing — Archiving — Architecture — Centralized server — Mobile hardware clients (TinyOS) — Layered XML messaging schema
  13. 13. “The networked sensor tapestry (NeST): a privacy enhanced software architecture for interactive analysis of data in video-sensor networks — Main concepts: — privacy buffer — privacy filters — privacy grammar — The utility of the architecture — variety of hardware/software clients — remote sensor interface device — software modules for sensor data — data visualization, sensor control — data archival applications
  14. 14. Preserving Privacy by De-identifying Facial Images — Algorithm to protect the privacy by de-identifying faces — Old approaches — Blacking out each face — covering eyes — randomly perturbing image pixels à fail for robustness of face recognition methods
  15. 15. Preserving Privacy by De-identifying Facial Images New approach - k-Same limits the ability of face recognition software. The algorithm • determines similarity between faces • creates new faces by averaging image components, • varying k.
  16. 16. Privacy through Invertible Cryptographic Obscuration — Scene distortion via cryptography — Encryption techniques to improve the privacy aspects Allowing full access Allowing general (i.e. violation of surveillance to privacy) only with use continue of a decryption key
  17. 17. Video surveillance using JPEG 2000 — JPEG 2000 compression — Events detection and ROI identification — Compressed video streams are scrambled and signed — Privacy — Data Integrity — Standards — JPSEC — JPWL
  18. 18. JPWL / JPSec Schema
  19. 19. Previous approaches with JPEG — The process — Identify ROI (people, privacy-sensitive info) — ROIs à Code-blocks — Code-blocks scrambled by ACL — Lowering quality layer of the codestream (bandwidth) — Drawback — Shape of the scrambled region is restricted to match code-block boundaries.
  20. 20. How we’ll make it better? — We want that — Scene remains understandable — The people are unidentifiable. — Security — private encryption key — Control who can unlock and view the whole scene in clear.
  21. 21. How we’ll make it better? — Output: single protected code-stream to all clients — No private key à distorted version of the content — Private key à unscramble the code-stream. — Can be used with — DCT-based: Motion JPEG, MPEG-4 or AVC 2x HD !! — DWT-based Motion JPEG 2000. 64 kBits 960 MBits — Goodies — Flexible Technique can be restricted to arbitrary-shape ROIs — Level of distortion (fuzzy to completely noisy)
  22. 22. Public/Private key encryption
  23. 23. Why Compress/Encode Video Source Output Data Rate[Kbits/sec] Quarter VGA @20 frames/sec 36 864.00 CIF camera @30 frames/sec 72 990.72 VGA @30 frames/sec 221 184.00 Transmission Medium Data Rate [Kbits/sec] Wireline modem 56 GPRS (estimated average rate) 30 3G/WCDMA (theoretical maximum) 384
  24. 24. MPEG-4 — Based on a motion compensation — Block-based DCT — Compression Predicted frames Intraframes
  25. 25. Four 8x8 Blocks for DCT 16x16 MacroBlocks
  26. 26. black with lot of change in frequency à DCT random matrix cosine function: horizontal, diagonal and vertical frequencies one color --> matrix with 1st large value & zeros
  27. 27. DCT cosine function: horizontal, diagonal and vertical frequencies Much of the signal energy lies at Low frequencies High frequencies. Often small to be neglected with a little distortion.
  28. 28. Human visual system experiments standard quantization matrix >50 less compress * (100-quality)/50 <50 more compress / lower quality * 50/quality
  29. 29. Quality factor of 75
  30. 30. Quality factor of 20
  31. 31. Quality factor of 5
  32. 32. Quality factor of 3
  33. 33. Entropy Encoder (Compress…) — Variable length Coding Huffman Coding or others…
  34. 34. Huffman Coding — The symbol with the highest probability is assigned the shortest code and vice versa. — Code words length is not fixed (VLC) — A codeword cannot be a prefix for another codeword (Self Synchronized Code)
  35. 35. Huffman Coding
  36. 36. Video Scrambling Earlier works Our approach — Traditional cryptographic — Bit scrambling techniques — Encrypt the compressed — Encrypt before compressing video. — Whole image completely — Whole scene remains distorted à indecipherable comprehensible but some objects cannot be identified — Coding performance — Complexity increase — Arbitrary-shape ROI — Flexible distortion
  37. 37. So when we scrambling? Before After Perform scrambling in the original Apply scrambling after encoding. (the image prior to encoding. compressed codestream is directly — Advantage: scrambled) Very simple and independent — Disadvantage: from the encoding scheme Very difficult to guarantee that the subsequently used. scrambled codestream will not — Disadvantage: crash a standard decoder. Significantly altering the statistics of the video signal, hence making the ensuing compression less efficient. Scrambling in the transform-domain. Region-based transform domain scrambling technique inverting the signs of selected transform coefficients
  38. 38. Transform-domain Scrambling — Frames transform using an energy compaction transform: DCT, DWT — The resulting coefficients are then entropy coded using techniques such as Huffman or arithmetic coding.
  39. 39. MPEG-4 & Scrambling — Effectively applied on the quantized DCT coefficients, and outside of the motion compensation loop
  40. 40. The scrambling recipe — What can be scrambled? — In general, DC coefficients are strongly correlated and are therefore unsuitable for scrambling. — Their signs are not.
  41. 41. The scrambling recipe — So what can be done? — All DC coefficients of the blocks corresponding to the ROIs are scrambled by pseudo-randomly flipping their sign.
  42. 42. The scrambling recipe — The shape of the scrambled region is restricted to match the 8x8 DCT blocks boundaries. — Level of scrambling = fewer AC coefficients.
  43. 43. Drifts… — Unauthorized decoder (not capable of unscrambling) will use a different motion compensation loop than an authorized decoder — Result: Unauthorized decoder may experience a drift, resulting in — artifacts in the scrambled sequence
  44. 44. How to avoid it? — Scrambled MB in the reference frame, are always INTRA coded. — Prevents the drift in motion compensation loop Predicted frames Intraframes
  45. 45. Encryption — PRNG initialized by a seed — SHA1PRNG with 64bit seed — Increase security à Multiple seed can be used — Seeds value encrypted using RSA — Inserted to the code-stream — Shape of ROI’s — Meta Data in MPEG-4 (private data / codestream) — Separate Channel
  46. 46. Complexity? — Flipping sings of selected coefficients
  47. 47. Scrambling — Effectively applied after the DWT and quantization, and before the arithmetic coder
  48. 48. De-Srambling — The process is fully reversible. At the decoder, authorized users have merely to perform the exact inverse operation.
  49. 49. Looks familiar? — Similar approach as proposed for MPEG-4 — Quantized wavelet coefficients are scrambled by pseudo randomly flipping their sign KM2 — Level of scrambling = fewer resolution levels.
  50. 50. Slide 56 ???? KM2 bandwith Kobi Magnezi, 10/06/2009
  51. 51. Goodies of JPEG2000 — The shape of the ROIs — Embedded ROI mechanism of JPEG 2000. — Leveraging standard JPEG security (JPSEC) — The seeds (for PRNG) can be encrypted and embedded in the codestream. à Fully JPSEC compliant.
  52. 52. Varying scrambling strength for MPEG-4
  53. 53. Varying scrambling strength for Motion HPEG 2000
  54. 54. Coding efficiency MPEG-4 Less than 10% bitrate increases
  55. 55. Coding efficiency Motion JPEG2000 Approximately 10% bitrate increases
  56. 56. Security Strength — Brute-force attack — tries all combinations reversing the signs of all non-zero AC coefficients. — CIF frame (352x288) — We consider the luminance component — MPEG-4 and Motion JPEG 2000 — à 99’792 AC coefficients. — ROI’s — Suppose that the attacker knows the ROIs which cover 5% of the image — à restricting the number of corresponding AC coefficients to 4’990. — Non-Zero — assuming that only 5 % of those are nonzero — Need to try reversing the signs of 250 coefficients à 2250 combinations for each frame. — à good level of security.
  57. 57. something to think about…
  58. 58. Eagle Eye

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