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On the (In)effectiveness of Mosaicing and Blurring as Tools for Document Redaction


In many online communities, it is the norm to redact names and other sensitive text from posted screenshots. Sometimes solid bars are used; sometimes a blur or other image transform is used. We consider the effectiveness of two popular image transforms - mosaicing (also known as pixelization) and blurring - for redaction of text. Our main finding is that we can use a simple but powerful class of statistical models - so-called hidden Markov models (HMMs) - to recover both short and indefinitely long instances of redacted text. Our approach borrows on the success of HMMs for automatic speech recognition, where they are used to recover sequences of phonemes from utterances of speech. Here we use HMMs in an analogous way to recover sequences of characters from images of redacted text. We evaluate an implementation of our system against multiple typefaces, font sizes, grid sizes, pixel offsets, and levels of noise. We also decode numerous real-world examples of redacted text. We conclude that mosaicing and blurring, despite their widespread usage, are not viable approaches for text redaction.

Open access
Towards Seamless Tracking-Free Web: Improved Detection of Trackers via One-class Learning

:// [8] Ghostery. [9] Ghostery 5.4.7 is ready to run! [10] Google Analytics. [11] Javascript Obfuscator. Dan’s tools, [12] Known Adblock Plus Subscriptions. https://adblockplus. org/subscriptions. [13] Moat. [14] NoScript. https

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(Do Not) Track Me Sometimes: Users’ Contextual Preferences for Web Tracking

. Privacy, trust, and self-disclosure online. Human- Computer Interaction, 25(1):1-24, 2010. [25] A. Lambrecht and C. Tucker. When does retargeting work? Information specificity in online advertising. Journal of Marketing Research, 2013. [26] P. Leon, B. Ur, R. Shay, Y. Wang, R. Balebako, and L. Cranor. Why Johnny can’t opt out: A usability evaluation of tools to limit online behavioral advertising. In Proc. CHI, 2012. [27] P. G. Leon, B. Ur, Y. Wang, M. Sleeper, R. Balebako, R. Shay, L. Bauer, M. Christodorescu, and L. F

Open access
An Automated Approach for Complementing Ad Blockers’ Blacklists

. Madhyastha, and V. Sekar. Understanding website complexity: Measurements, metrics, and implications. In Proc. IMC ’11 , pages 313–328, 2011. [9] R. Cookson. Google, Microsoft and Amazon pay to get around ad blocking tool. Financial Times (2015-02-01), . Accessed: 2015-02-15. [10] M. E. Crovella and A. Bestavros. Self-similarity in world wide web traffic: evidence and possible causes. IEEE/ACM Trans. Netw. , 5(6):835–846, 1997. [11] J. Demšar, T. Curk, A. Erjavec, Črt Gorup, T. Hočevar

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Automated Experiments on Ad Privacy Settings
A Tale of Opacity, Choice, and Discrimination

. Dubourg, J. Vanderplas, A. Passos, D. Cournapeau, M. Brucher, M. Perrot, and E. Duchesnay, “Scikit-learn: Machine learning in Python,” Journal of Machine Learning Research, vol. 12, pp. 2825-2830, 2011. [10] E. Jones, T. Oliphant, P. Peterson et al., “SciPy: Open source scientific tools for Python,” 2001, [11] M. C. Tschantz, A. Datta, A. Datta, and J. M. Wing, “A methodology for information flow experiments,” ArXiv, Tech. Rep. arXiv:1405.2376v1, 2014. [12] P. Good, Permutation, Parametric and

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Social Engineering Attacks on Government Opponents: Target Perspectives

. Cox, “A Hacker Claims to Have Leaked 40GB of Docs on Government Spy Tool FinFisher,” Aug. 2014. [Online]. Available: [8] A. Greenberg, “Hacking Team Breach Shows a Global Spying Firm Run Amok,” Jul. 2015. [Online]. Available: [9] FinFisher, “Remote Monitoring & Infection Solutions: FinFly ISP,” Spy Files, 2011, accessed: 30-August-2016. [Online]. Available

Open access
Analyzing Remote Server Locations for Personal Data Transfers in Mobile Apps

Tool. help/monkey.html, 2015. [22] Ben Gruver. Smali/Baksmali Tool., 2015. [23] Dominik Herrmann and Jens Lindemann. Obtaining personal data and asking for erasure: Do app vendors and website owners honour your privacy rights? CoRR, abs/1602.01804, 2016. [24] Paul De Hert and Vagelis Papakonstantinou. The proposed data protection Regulation replacing Directive 95/46/EC: A sound system for the protection of individuals. Computer Law & Security

Open access
Portrait of a Privacy Invasion
Detecting Relationships Through Large-scale Photo Analysis

, 1997. Proceedings., 1997 IEEE Computer Society Conference on, pages 130-136. IEEE, 1997. [20] B. Rouberol. Comparison of face detection tools. [21] H. A. Rowley, S. Baluja, and T. Kanade. Neural networkbased face detection. Pattern Analysis and Machine Intelligence, IEEE Transactions on, 20(1):23-38, 1998. [22] M. Turk and A. Pentland. Eigenfaces for recognition. Journal of cognitive neuroscience, 3(1):71-86, 1991. [23] T. Verge. The new Snapchat brilliantly mixes video and texting

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Every Move You Make: Exploring Practical Issues in Smartphone Motion Sensor Fingerprinting and Countermeasures

: a free network mapping and security scanning tool. . [28] S.B. Moon, P. Skelly, and D. Towsley. Estimation and removal of clock skew from network delay measurements. In Proceedings of the 18th Annual IEEE International Conference on Computer Communications (INFOCOM) , pages 227–234, 1999. [29] Keaton Mowery and Hovav Shacham. Pixel perfect: Fingerprinting canvas in HTML5. In Proceedings of Web 2.0 Security and Privacy Workshop (W2SP) , 2012. [30] Nick Nikiforakis, Luca Invernizzi, Alexandros Kapravelos, Steven Van Acker

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Individual versus Organizational Computer Security and Privacy Concerns in Journalism

-generation onion router,” in Proceedings of the 13th USENIX Security Symposium, 2004. [25] N. Unger, S. Dechand, J. Bonneau, S. Fahl, H. Perl, I. Goldberg, and M. Smith, “SoK: Secure Messaging,” in Proceedings of the IEEE Symposium on Security and Privacy, 2015. [26] M. Brennan, K. Metzroth, and R. Stafford, “Building Effective Internet Freedom Tools: Needfinding with the Tibetan Exile Community,” in 7th Workshop on Hot Topics in Privacy Enhancing Technologies (HotPETs), 2014. [27] Internews Center for Innovation & Learning

Open access