Televisions, Video Privacy, and Powerline Electromagnetic Interference

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Evelyn Pitts
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1 Televisions, Video Privacy, and Powerline Electromagnetic Interference Miro Enev, Sidhant Gupta, Yoshi Kohno, & Shwetak Patel Security & UbiComp UW

2 Smart Home = Smart Devices + Smart Sensors

3 The Picture Today power sensor Utility 3 rd Parties

4 The Picture Today power sensor Utility UbiComp 3 rd Parties

5 Emerging Trends: Sophisticated electrical sensors are already deployed in homes to help achieve new efficiency and utility goals. Benefactors:

6 Research Q: What private information is available from the powerline?

7 Research Q: What private information is available from the powerline? Answer: Modern TVs leak substantial information on the power line that is indicative of the screen content

8 Research Q: What private information is available from the powerline? Answer: Modern TVs leak substantial information on the power line that is indicative of the screen content Information can be collected using a single sensor installed anywhere on power line

9 What s the BIG deal? U.S. Video Protection & Privacy Act of 1998 states that video viewing records be kept private

10 What s the BIG deal? U.S. Video Protection & Privacy Act of 1998 states that video viewing records be kept private We hope our work can inform future discourse about the directions of Powerline sensing technologies

11 Smart Sensor Power measurements reveal private information about homeowner s activity [Markham 2010]; concurrent work also looks at TVs [Greveler 2011] In-line power measurement of a PC can reveal web browsing habits [Clark 2011]

12 Power Based Measurement In-line with device

13 Home s Powerline Infrastructure Voltage Based Measurement... Parallel with device

14 Switched Mode Power Supply

15 Switching Circuits generate high frequency Electro Magnetic Interference (EMI) Supply Load Inductor

16 Switching Circuits generate high frequency Electro Magnetic Interference (EMI) Supply Load Inductor

17 Switching Circuits generate high frequency EMI which couples onto the powerline Supply Load Inductor Home s Power Line Infrastructure

18 Switching Circuits generate high frequency EMI which couples onto the powerline Supply Load we record the EMI Inductor Home s Power Line Infrastructure

19 EMI: Summary ElectriSense (2010 Gupta et al. ) Many modern devices produce EMI! EMI can be collected with a single sensor! Frequency (khz) Signals live in the frequency domain!

20 Home

21 TV EMI Video Movie Link

22 Our 8 TVs 58 Samsung 58-A Samsung 58-B Plasma, Panasonic 42-A Panasonic 42-B Sharp Sharp 32-A Sharp 32-B Samsung 32 LCD,

23 Research Questions? Q1: Do TVs produce repeatable EMI given repeated screen content? Q2: For a given TV, does different screen content produce different EMI? Q3: Is EMI consistent across TVs from the same model family? Q4: Can we use EMI to determine what is being watched on TV? Q5: Can we match lab EMI to EMI recorded in various home settings?

24 Research Questions? Q1: Do TVs produce repeatable EMI given repeated screen content? Q2: For a given TV, does different screen content produce different EMI? Q3: Is EMI consistent across TVs from the same model family? Q4: Can we use EMI to determine what is being watched on TV? Q5: Can we match lab EMI to EMI recorded in various home settings?

25 Screen Content = 20 IMDB Top Grossing Movies Action Animation Comedy Documentary Drama

26 Lab Setup (I)Isolation transformer - external EMI filter (A)Power Line Interface - custom voltage sensor (U) Universal Software Radio Peripheral - analog to digital convertor (A)Spectrum analyzer - visualization & logging

27 Time (secs) Signal Extraction Frequency (khz)

28 Time (secs) Signal Extraction Frequency (khz)

29 Extracting TV EMI

30 Extracting TV EMI

31 Research Questions? Q1: Do TVs produce repeatable EMI given repeated screen content? Q2: For a given TV, does different screen content produce different EMI? Q3: Is EMI consistent across TVs from the same model family?

32 Q4: Can we use EMI to determine what is being watched on a TV?

33 Q4: Can we use EMI to determine what is being watched on a TV? Approach: Match EMI to a DB

34 Building an EMI Database EMI Time (mins.)

35 Multiple Runs Multiple TVs Same Content Pan42A 0 Time (mins.) 60 Pan42B

36 Multiple Runs Multiple TVs Same Content Pan42A 0 Time (mins.) 60 Pan42B Query vs DB

37 Query vs DB TV 1: 8 Movie 1:20 Q.Len 1:60 =? 0 Time (mins.) 15

38 Query vs DB TV 1: 8 Movie 1:20 Q.Len 1:60 =? 0 Time (mins.) 15

39 Query vs DB TV 1: 8 Movie 1:20 Q.Len 1:60 =? 0 Time (mins.) 15 Best match

40 Possible Query Results Hit: the search engine is confident* in the match (accept) and the match was the movie from which the query itself was extracted. (Success.) Miss: the search engine is confident* in the match (accept) but there is a mismatch between the search engine s best guess and the query origin. (Failure.) Reject: the best match was a not a clear winner*, and the matching algorithm chooses not to respond. (Neither success nor failure.) * Confidence is the gap size between the top match and the runner up

41 Query Length & Confidence Confidence is the gap size between the top match and the runner up Query Length 1 min 6 min 12 min 15 min Reject Reject Reject Reject

42 Q4: Can we determine what is being watched from EMI?

43 Q4: Can we determine what is being watched from EMI?

44 Q5: Can we match lab EMI to home EMI?

45 Home Details Style Year Built Size Single family Home sq. ft Apartment sq. ft. Multi-family Home sq. ft.

46 Home Setup

47 Home Setup

48 Q5: Can we match lab EMI to EMI recorded in home settings

49 Extensions: Can we predict EMI from screen content without a TV?

Predicting EMI Extract Features Train Model Predict EMI Input Features:

Flux: change in brightness between consecutive frames Edge Intensity:

Color: mean and standard deviation for Gaussians fitted to R, G, and B

50 Predicting EMI Extract Features Train Model Predict EMI Input Features: Model: Neural Net Brightness: cumulative sum of averaged RGB intensities Flux: change in brightness between consecutive frames Edge Intensity: pixelsum of a Canny Edge filter FFT: slope of the best fit line to an FFT Color: mean and standard deviation for Gaussians fitted to R, G, and B color histograms Bitrate: kbits/second computed using FFMPEG Cross Validation: 10 Train, 5 Test

51 Predicting EMI

52 Predicting EMI

53 TV EMI: Theory of Operation SMPS use light scene save dark scene TV EMI Backlight (brightness) is key source of TV EMI

54 Defenses and Tensions > Better filtering by power supplies > Signal Injection & Jamming (Energy Star) > Battery Masking [Mclaughlin 2011] > Infrequent sensor readings

55 Takeaways > Devices produce EMI on the powerline > Single sensor tracks many devices > EMI can be > Growing attack surface

56 Questions?

57 Does EMI matching scale?

58 Does EMI matching scale?

59 Sharp 32 and SNR

60 Related Work Our research shows that the analysis of the household s electricity usage profile does reveal what channel the TV set in the household was displaying.

61 EMI Q1: repeatable EMI from repeated screen content? A & B : Lion King C: Bourne Ultimatum Cross Correlation Time (secs)

62 TVs (1) 58 Samsung 58-A B

63 TVs (2) 42 Panasonic 42-A B

64 TVs (3) 32 Sharp 32-A B

EMI/EMC diagnostic and debugging

EMI/EMC diagnostic and debugging 1 Introduction to EMI The impact of Electromagnetism Even on a simple PCB circuit, Magnetic & Electric Field are generated as long as current passes through the conducting