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Mimesis Aegis: A Mimicry Privacy Shield A System's Approach to Data Privacy on Public Cloud

Mimesis Aegis: A Mimicry Privacy Shield A System's Approach to Data Privacy on Public Cloud Billy Lau, Simon Chung, Chengyu Song, Yeongjin Jang, Wenke Lee, and Alexandra Boldyreva USENIX 14 Presenter: Shasha Wen. Some figures are from the author's slides. Outline. Motivation Related work

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Mimesis Aegis: A Mimicry Privacy Shield A System's Approach to Data Privacy on Public Cloud

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  1. Mimesis Aegis: A Mimicry Privacy Shield A System's Approach to Data Privacy on Public Cloud Billy Lau, Simon Chung, Chengyu Song, Yeongjin Jang, Wenke Lee, and Alexandra Boldyreva USENIX 14 Presenter: Shasha Wen Some figures are from the author's slides

  2. Outline • Motivation • Related work • M-Aegis • System design • implementation • Evaluation • Limitation • Conclusion

  3. Motivation • Public cloud services(PCS) • Trust server to secure our data • Conflict of interest for data privacy between users and PCS providers • Text communication service • Smart phone

  4. Change the status • End to end encryption • Hard in practical • Good solution • Users' ease-of-use • Developers' effort to maintain support • Feasibility and deployability of solution on a mobile system

  5. Design goals For a solution to be secure, it must be properly isolated from untrusted entities 1 For a solution to be adoptable, it must preserve the user experience 2 For a solution to be sustainable, it must be easy to maintain and scalable 3

  6. Outline • Motivation • Related work • M-Aegis • System design • implementation • Evaluation • Limitation • Conclusion

  7. Related work • Standalone solutions • Protect data confidentiality • Good isolation from untrusted entities • e.g. Gibberbot, TextSecure, SafeSlinger...... • Problem • Not preserve user experience 1

  8. Related work • Browser Plugin/Extension Solutions • e.g. Cryptocat, Scramble, NOYB...... • Provides transparent integration • Problem • Not applicable to mobile platform • App repackaging/Rewriting solution • e.g. Aurasium, Dr. Android...... • Problem • Breaks app updates • Isolation model is unclear 2 2

  9. Outline • Motivation • Related work • M-Aegis • System design • Implementation • Evaluation • Limitation • Conclusion

  10. Mimesis Aegis • Apply end-to-end encryption while preserving user experience • Mimicking GUIs of app of interest • Interacting with app on behalf of user • Good isolation model • Generalizable across different apps • Resilient to app updates 2 1 3

  11. Mimesis Aegis

  12. M-AegisSystem Design-Threat Model • In-scope • Untrusted parties • Public cloud service providers • Client side apps • Middle boxes between a PCS and client side app • Trusted components • Hardware, OS, keyboard, M-Aegis components, the user • Out of scope • availability(denial-of-service) • Attacks against our TCB

  13. M-AegisSystem Design-Architecture • Layer 7.5 • User interface automation/accessibility(UIA) • Secure • No developer attention • Users' sense

  14. M-AegisSystem Design-Architecture • Layer 7.5 • Interactions without data confidentiality • click-through • Interactions with data confidentiality • Place opaque GUIs in different color • Interactions with control GUIs • Semi-transparent mimic GUIs

  15. M-AegisSystem Design-Architecture • UI Automation Manager(UIAM) • Give M-Aegis the context of the screen • TCA, GUI tree, content of the GUI • Provide information to correctly render GUIs • Per-Target Client App(TCA) Logic • Handle direct user input • Decides suitable actions • Pass or encode • Encryption and encoding scheme

  16. M-AegisSystem Design-Architecture • Cryptographic Module • Key manager • Per TCA • Password based(default) to more sophisticated one • Searchable Encryption Scheme • Easily-deployable efficiently-searchable symmetric encryption(EDESE)

  17. Searchable Encryption Scheme • Normal encryption • “ab”, ”abc” • Bellare et al[1] • keywords • HMACs of unique keywords • Add dummy keywords • Bloom filter(BF) • Efficient set-inclusion tests • Encodes the positions of on-bits in a BF [1] BELLARE, M., BOLDYREVA, A., AND O’NEILL, A. Determin- istic and efficiently searchable encryption. In CRYPTO (2007), A. Menezes, Ed., vol. 4622 of Lecture Notes in Computer Sci- ence, Springer, pp. 535–552.

  18. Searchable Encryption Scheme • Bloom filter(BF) • Keyword:128bit • BF: 224 • k: 10 From http://en.wikipedia.org/wiki/Bloom_filter

  19. M-AegisSystem Design- User Workflow User L7.5 Per-TCA logic UIAM App launch the Gmail initialize detect composing Mimic GUI Detect state send Mimic GUI Send to app; Click “send” Get content; Get the key; encode UI

  20. M-AegisImplementation • UIAM based on UIA libraries • Monitor events • WINDOW_CONTEST_CHANGED • WINDOW_STATE_CHANGED • VIEW_SCROLLED • Query for UI node • Resource ID ← UI Automator Viewer • performAction() • Layer 7.5 always-on-top • Creation of various system windows • TYPE_SYSTEM_OVERLAY • TYPE_SYSTEM_ERROR

  21. M-AegisImplementation • Per-TCA Logic • Identify signatures for each TCA state • Event handler • Type of input data • Encrypt data into CJK unicode • Cryptographic Schemes • AES-GCM-256 • PBKDF2 & SHA-1 as HMAC

  22. Outline • Motivation • Related work • M-Aegis • System design • Implementation • Evaluation • Limitation • Conclusion

  23. M-AegisEvaluations-Performance • Experimental Setup: • Stock Android phone(LG Nexus 4) • Android 4.4.2(Kit Kat, API level 19) • Repeat 10 times and take average • Preview Encrypted Email • 76 ms to render plaintext on L-7.5 • Well with expected response time(50-150ms) • Composing and Sending Encrypted Email • With longest email: • 953 words, of which 362 are unique • 205 ms to encrypt, build the search index, and encode

  24. M-AegisEvaluations-User Study • Users: college students • Tasks: previewing, reading, composing, sending and searching • Difference and experience • Report from 15 participants • No one notice major difference • One: L-7.5 didn't catch up smoothly when scrolled • One: L-7.5 lag when reading emails • All would use M-Aegis to protect the privacy of their data

  25. Outline • Motivation • Related work • M-Aegis • System design • Implementation • Evaluation • Limitation • Conclusion

  26. Limitation • Data format • text(Unicode-compatible) • Not support other types(e.g. Image, audio, video) • Unavailability of transformation functions • Other process steps, like compression • Typographical error during search • Rare happen • Encryption schemes that tolerate typographical error search without server modification

  27. Outline • Motivation • Related work • M-Aegis • System design • Implementation • Evaluation • Limitation • Conclusion

  28. Conclusion • Users can control private data using Mimesis Aegis • Layer 7.5 • Strong isolation • Preserve original user experience • Scalar to more apps and resilient to app updates • Prototype on Android • Minimal overhead • User study shows acceptable

  29. Questions?

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