1. ANONIZE: A Large-Scale Anonymous Survey System
Susan Hohenberger :Johns Hopkins University
Steven Myers : Indiana University
Rafael Pass : Cornell University
Abhi shelat : University of Virginia
Paper cited 1 time.

2. Topics Requirements for Ad-hoc Surveys. Prior Work.
Intro to Ad-hoc Surveys.
Background Review.
Ad-hoc Surveys in More Details.
How Each Property is Achieved.
Implementation.
Performance Evaluation.
Topics

3. Objective
Enables a survey authority to independently select a group of registered users and create a survey in which only selected users can anonymously submit exactly one response.

4. Each user should be allowed to submit only once.
Authenticity: ensuring that only the legitimate users can participate in the data collections.
Anonymity: ensuring that the there is no link between the legitimate user and his/her data,even if an RA and SA are arbitrarily corrupted and in collusion, (honest feedback!)
Each user should be allowed to submit only once.
Yet must be anonymous!
Requirements
nonymitAnonymiAnokkkkkmmmmmjjjjjnymity: ensuring that the there is no link between the legitimate uty: ensuring that the there is no link between the legitimate uy: the there is no link between the legitimate user and his/her data (honest feedback!)ensuring that the therensuring that the there is no link between the legitimate user and his/her data (honest feedback!)e is no link between the legitimate user and his/her data (honest feedback!)

5. online product reviews.
Course Evaluation.
online product reviews.
Whistleblowing ( Verify that a complaint comes from within the organization)
Example
nonymitAnonymiAnokkkkkmmmmmjjjjjnymity: ensuring that the there is no link between the legitimate uty: ensuring that the there is no link between the legitimate uy: the there is no link between the legitimate user and his/her data (honest feedback!)ensuring that the therensuring that the there is no link between the legitimate user and his/her data (honest feedback!)e is no link between the legitimate user and his/her data (honest feedback!)

6. Issue with Third Party. Collect usernames during submission
Computer might be stolen.
Happened at Cornell University. Contains sensitive data of 45,000 university members.
Side Channel indicate who already filled the form (order in which students participated).
Jurisdictional boundaries (No sensitive data to be stored on servers run by foreign corporations)
if data stripped, No way to verify of multiple submission.
nonymitAnonymiAnokkkkkmmmmmjjjjjnymity: ensuring that the there is no link between the legitimate uty: ensuring that the there is no link between the legitimate uy: the there is no link between the legitimate user and his/her data (honest feedback!)ensuring that the therensuring that the there is no link between the legitimate user and his/her data (honest feedback!)e is no link between the legitimate user and his/her data (honest feedback!)

7. Solution: Cryptography. No need to Trust Third Party.

8. Prior Work 1) Authenticate 2) Get Token 3) Participate
User authenticate to server anonymously.
User use token to participate on survey.
1) Authenticate
2) Get Token
3) Participate
User check out single use token.
Good ... as long as step 2 & 3 separated with long time. However, this make it inconvenience.

9. Proposed Solution: Ad-hoc survey
Anyone can select group and create survey.
Only those can complete the survey at most once!
Survey initiator initiate survey knowing only identities ( ).
No further interaction required!
Hence, increase user participation.
nonymitAnonymiAnokkkkkmmmmmjjjjjnymity: ensuring that the there is no link between the legitimate uty: ensuring that the there is no link between the legitimate uy: the there is no link between the legitimate user and his/her data (honest feedback!)ensuring that the therensuring that the there is no link between the legitimate user and his/her data (honest feedback!)e is no link between the legitimate user and his/her data (honest feedback!)

10. Ad-hoc Surveys: Actor Role
RA - Registration Authority (ex, University)
Issue master user token.
SA -Survey Authority- Course Administrator.
Create Surveys.
Users
Provide surveys data.

11. Ad-hoc Surveys: Step 1(one time)
Register ( e.x )
User
(e.x student)
2) secret master user token (unlinkable)
RA (Registration Authority)
(e.x University)
Token used for all surveys

12. Ad-hoc Surveys: Step 2 (Repeated)
Choose Survey ID SA
(e.x Course Administrator)
Choose List of identities (e.x )

13. Ad-hoc Surveys: Step 3 (Repeated)
survey key + master user token = one-time token (No interaction)
submit (Non interactively)
User
one-time token, properties:
No link to student identity.
For given survey, one token.
Anonymous network like Tor. SA

14. Background: Tor (Anonymity network).
Tor is free software for enabling anonymous communication.
Name derived from: The Onion Router.
Directs Internet traffic through a free, worldwide, volunteer network consisting of more than 6,000 relay.
NSA:"the King of high-secure, low-latency Internet anonymity" with "no contenders for the throne in waiting"

15. Background: Commitment Scheme.
Allows one to commit to a chosen value (or chosen statement) while keeping it hidden to others, with the ability to reveal the committed value later

16. Background: Commitment Scheme.
Example: Coin flipping.
Not in the same place:
Alice "calls" the coin flip but only tells Bob a commitment to her call.
Bob flips the coin and reports the result.
Alice reveals what she committed to.
Bob verifies that Alice's call matches her commitment
If Alice's revelation matches the coin result Bob reported, Alice wins.
If they are physically in the same place:
Alice "calls" the coin flip.
Bob flips the coin.
If Alice's call is correct, she wins, otherwise Bob wins.

17. Background: Pseudo-random functions (PRF)
A PRF is a seeded deterministic function that maps any input to a random looking output, assuming one has no knowledge of the seed.
This is the intuition behind pseudo-random functions: Bob gives alice some random i, and Alice returns FK(i), where FK(i) is indistinguishable from a random function, that is, given any x1,...,xm,FK(x1),...,FK(xm), no adversary can predict FK(xm+1) for any xm
Used for symmetric encryption.

18. Background:non-interactive zero-knowledge NIZK
Non-interactive zero-knowledge (NIZK) proofs are a variant of zero-knowledge proofs in which no interaction is necessary between prover and verifier.
Common reference string shared between the prover and the verifier is enough to achieve computational zero-knowledge without requiring interaction.

19. Background: Blind signature
blind signature is a form of digital signature in which the content of a message is disguised (blinded) before it is signed. The resulting blind signature can be publicly verified against the original, unblinded message in the manner of a regular digital signature.
Typically employed in privacy-related protocols where the signer and message author are different parties.
Examples include cryptographic election systems.

20. Registration- More Details: Step 1(one time)
2)Register:
send commitment to random seed sid PRF
Provide NIZK that commitment is well formed.
1.Generate public key pair.
3) sign the commitment with its sign key (Blind signature).
User
(e.x student)
4) signature: master user token (unlinkable)
RA (Registration Authority)
(e.x University)
Token used for all surveys

21. Ad-hoc Surveys - More Details: Step 2 (Repeated)
Choose Survey ID (vid) SA
(e.x Course Administrator)
Choose List of identities (e.x ) called “L”

22. Ad-hoc Surveys - More Details: Step 3 (Repeated)
submit m (Non interactively)
User
survey key (vid) + master user token = one-time token (No interaction)= Fsid (vid) (Evaluate PRF using seed sid with input vid )
Present NIZK proof that “it knows a signature by the RA on it’s identity id and a commitment to a seed sid”.
NIZK also proof “it’s signed by the SA on it’s id (meaning id is on the L)
Thereby user data is authenticated by NIZK. SA

23. How Each Property is Achieved.
Only authorized users complete survey
NIZK (Tag based).
User can complete survey at most once
One user token. PRF always give same value, computed from s.
Anonymity.
Neither RA nor SA see the seed (only see commitments),
Zero-knowledge property.
Pseudo-random property of PRF.

24. Implementation: System setup-
Implementation: System setup
RA generate public key-pair pkRA (public), skRA(private).
Each SA generate public key-pair pkSA, skSA.

25. Implementation: User Registration-
Implementation: User Registration
User and RA execute the protocol (RegRA, RegU).
which allow user will get unlinkable “master credential” credid.

26. Implementation: Survey Registration-
Implementation: Survey Registration
SA generate a “survey public key”.
Or pksid GenSurvey(1n, sid, L, skSA)
survey ID.
SA private key.

27. Implementation: Complete Survey-
Implementation: Complete Survey
User combined master credential credid with survey identifier sid to generate one time token.
Or sub = (tok,m,tokauth) submit(1n, sid,pksid, m,credid)
Submit Sub to SA through anonymous channel.
If they are physically in the same place:
Alice "calls" the coin flip.
Bob flips the coin.
If Alice's call is correct, she wins, otherwise Bob wins.
tok: one time token.
tokauth: authenticator to bind m to tok.

28. Implementation: Audit-
Implementation: Audit
User could check if submission counted by inspecting their submission output.
User use Check (pkSA,pkRA,sid,pksid,sub) to check if sub is valid submission (No ballout/survey-stuffing)
User could use Authorized( pkSA,sid,pksid,id’) to check user id’ is authorized to do survey (result not targeted to particular user).
If they are physically in the same place:
Alice "calls" the coin flip.
Bob flips the coin.
If Alice's call is correct, she wins, otherwise Bob wins.

29. Concrete Implementation:
Implemented in C++ using MIRCALE big number library.
Supports pairing (bilinear map)-based cryptography.
Free for Educational purpose.
If they are physically in the same place:
Alice "calls" the coin flip.
Bob flips the coin.
If Alice's call is correct, she wins, otherwise Bob wins.
Maps a vector space X into another space Y.
There are no practical limits to the precision except the ones implied by the available memory in the machine.

30. Performance: Timing Result
Barreto–Lynn–Scott pairing curve
Barreto– Naehrig pairing curve
degree k=12,
Verify 1 million submissions in approximately 33 hours per CPU core.

31. Thank You.