1. Deniability an Alibi for Users in P2P Networks
Information Systems Engineering Ben-Gurion University
Deniability an Alibi for Users in P2P Networks
Ofer Hermoni,
Eyal Felstaine, Niv Gilboa and Sharon Shitrit
January 1, 2019

2. Outline Introduction Deniability Conclusion Architecture & Shares
Operations
Performance
Mathematics
Conclusion

3. P2P Network Client-Server model: e.g. web-surfing, email…
P2P Network: e.g. File-sharing, instant messaging, VoIP…

4. The Problem – Anonymity in P2P
Reader anonymity
Server anonymity 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

5. Deniability
Deniability
Deniability

6. Categories All documents are distinguished to two categories:
Non-controversial
Censored

7. Architecture 5 1 6 2 7 3 8 4

8. Publishing Non-Controversial Content1 2 4 3 f
8553 22
872
455
9953
6663
Pool of shares

9. Publishing Censored Content1 2 5 8 6 5 f f 7
8553 22
872
455
9953
6663
Pool of shares

10. Retrieval Censored Content
Needed: “Lord of the Rings”
Query the Index
Retrieving: “Mars Car” + “Baby” 1 2 5 6 4 3 8 7
Server
Share
Doc name
A, C 1
Mars Car B 2
D, F 3 G 4
A, B 5
Baby 6 C 7
D, G 8
Lord of the Rings

11. Deniability The reader maintains “Reader Deniability” - why?
The reader retrieves only non-controversial documents
The server maintains “Server Deniability” - why?
Every served share is associated with a non-controversial document
Indexing

12. Performance t - threshold = 2 |d| - Doc. size 4|d| bits 2|d| bits
Including Indexing deniability
Without Indexing deniability
Censored
Non-controversial
4|d| bits
2|d| bits
3|d| bits
Communication Insert
Communication Retrieve
|d| bits
Storage
O(|d|)
Computation (Insert / Retrieve)
t - threshold = 2
|d| - Doc. size

13. Shamir’s Secret Sharing (1979)
f(x) = 2 degree polynomial
f(x)
f(2)
f(3)
f(4)
f(1)
secret
f(5) x 1 2 3 4 5
Minimum 3 points needed to reconstruct f(x)
formulas

14. Function f - Deniable Secret Sharing
f(x)
f(x) = 2 degree polynomial
Without index deniability x 1 2 3 4 5
formulas

15. Conclusion Deniability – An elegant alternative to anonymity
Reader, Server and index deniability
Against any adversary
Low overhead
Storage: x2 at most (x4 including index deniability)
Communication: x4 at most
Can be a “plug-in” to ubiquitous P2P networks

16. The End
Thank you!!!