1. Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks - I CS 436/636/736 Spring 2012 Nitesh Saxena Some slides borrowed from Philippe Golle, Markus Jacobson

2. Course Admin Mid-term graded – Scores posted – To be distributed today – Stats: Mean 87.75; Median 92.5 HW3 to be posted in the next few days 5/3/20152 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

3. A Case History: AOL Web Search Query Log Leakage AOL's disturbing glimpse into users' lives, CNET News, August 7, 2006 AOL's disturbing glimpse into users' lives, CNET News, August 7, 2006 – 21 million search queries posed over a 3-month long period; 650,000 users – No user identification information released per se, but?? Search Log still available: – http://www.gregsadetsky.com/aol-data/ http://www.gregsadetsky.com/aol-data/ 5/3/20153 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

4. Other Scenarios where privacy is important Location-based search Web browsing Electronic voting Electronic payments Email conversation … 5/3/2015 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks 4

5. Today’s Outline Anonymizing Network (or Mix Network) Anonymizing Network Applications Requirements Robustness Types of Anonymizing Networks – Decryption based (Onion Routing) – Re-encryption based 5/3/20155 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

6. Definition: Mix Server (or Relay) 5/3/20156 A mix server: Receives inputs Produces “related” outputs The relationship between inputs and outputs is secret InputsOutputs ? Mix Server Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

7. Definition: Mix Network 5/3/20157 Mix network A group of mix servers that operate sequentially. Server 1Server 2Server 3 InputsOutputs ??? Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

8. Applications Hide:  “who voted for whom?”  “who paid whom?”  “who communicated with whom?”  “what is the source of a message?” Good for protecting privacy for election and communication Used as a privacy building block 5/3/20158 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

9. Electronic Voting Demonstration 1.“Who do you like best?” 2.Put your ballot into a WHITE envelope and put again in a RED one and sign on it 5/3/20159 Jerry  Washington  Lincoln  Roosevelt Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

10. Electronic Voting Demo. (Cont’d) Administrators will 1.Verify signatures together 2.1 st Admin. shuffles and opens RED envelopes 3.Send them to 2 nd Admin. 4.2 nd Admin. shuffles again and opens WHITE envelopes 5.Count ballots together 5/3/201510 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

11. A real system for elections Sign voter 1 (encr(encr (vote 1 ))) Sign voter 2 (encr(encr (vote 2 ))). Sign voter n (encr(encr (vote n ))) 5/3/201511 Jerry vote 1 vote 2 vote 3. vote n Mix Net  Washington  Lincoln  Roosevelt Mix Net

12. “Choose one person you like to pay $5” Put your ballot into an WHITE envelope and put again in a RED one and sign on it 5/3/201512 Jerry Name of the person ( ___________ ) Electronic Payment Demo. Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

13. Electronic Payment Demo. (Cont’d) Administrators will 1.Verify signatures together 2.Deduct $5 from each account 3.1 st Admin. shuffles and opens RED envelopes 4.Send them to 2 nd Admin. 5.2 nd Admin. shuffles again and opens WHITE envelopes 6.Credit $5 to recipients 5/3/201513 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

14. For Payments Sign payer 1 (encr(encr (payee 1 ))) Sign payer 2 (encr(encr (payee 2 ))). Sign payer n (encr(encr (payee n ))) 5/3/201514 payee 1 payee 2 payee 3. payee n DEDUCTDEDUCT Credit Jerry Name (________ ) Mix Net

15. For email communication encr (email 1, addressee 1 ) encr (email 2, addressee 2 ). encr (email n, addressee n ) 5/3/201515...... Mix Net Deliver To: Jerry Don’t forget to have lunch.

16. Other Uses Anonymous web browsing; web searching (Anonymizer)Anonymizer 5/3/201516 From LPWA homepage Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

17. Other Uses (Cont’d) 5/3/201517 Location privacy for cellular devices – Location-based service is GOOD ! Landline-phone calling to 911 in the US, 112 in Europe All cellular carrier since December 2005 – RISK ! Location-based spam Harm to a reputation Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

18. Other Uses Anonymous VoIP calls Anonymous acquisition of security patches 5/3/201518 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

19. Other uses (Cont’d) Sometimes abuses Avoid legislation (e.g., piracy) P2P sharing of copyright content Terrorism: communication with media – Mumbai attacks Mumbai attacks 5/3/201519 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

20. Principle 5/3/201520 Chaum ’81 Message 1 Message 2 server 1server 2server 3 Privacy Efficiency Trust Robustness Requirements :

21. Requirements 1.Privacy Nobody knows who said what 2.Efficiency Mixing is efficient (= practically useful) 3.Trust How many entities do we have to trust? 4.Robustness Will replacement cheaters be caught? What if a certain number of mix servers fail? 5/3/201521 Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

22. But what about robustness? encr(Berry) encr(Kush) 5/3/201522 Kush STOP I ignore his output and produce my own There is no robustness!

23. Zoology of Mix Networks Decryption Mix Nets [Cha81,…]: – Inputs: ciphertexts – Outputs: decryption of the inputs. Re-encryption Mix Nets[PIK93,…]: – Inputs: ciphertexts – Outputs: re-encryption of the inputs 5/3/201523 InputsOutputs ? Lecture 7.1: Privacy and Anonymity Using Anonymizing Networks

24. First Solution 5/3/201524 Chaum ’81, implemented by Syverson, GoldschlagSyverson, Goldschlag Not robust (or: tolerates  cheaters for correctness) Requires every server to participate (and in the “right” order!)