Secure Wireless Communication with Dynamic Secrets

1. Sheng Xiao, Weibo Gong and Don Towsley,2010 Infocom Secure Wireless Communication with Dynamic Secrets

2. Outline • Problem statement • Overview • Dynamic secrets • Extraction • Collection • Amplification • System secret protection • Bootstrapping security and implementation • Summary and conclusion

3. Problem statement • Data security in wireless communication • Security mechanism desirable in the case of secret leakage • Solution: use dynamic secrets, based on the link layer communications between wireless devices

4. Related Work • Prior work uses the wireless physical channel properties for secret sharing • However, they usually demand special hardware upgrades or at least specific interfaces to provide channel measurement information.

5. Related Work • Instead of working with the physical layer channel model to calculate the secret capacity, we shift attention to the link layer and emphasize the dynamics of secrets. • In wireless communication, it is practically impossible to eavesdrop link layer communication for a long periodwithout errors • The single-point of failure occurs at the attackers

6. Outline • Problem statement • Overview • Dynamic secrets • Extraction • Collection • Amplification • System secret protection • Bootstrapping security and implementation • Summary and conclusion

7. Series of Dynamic Secrets • Let Hk indicates how many bits the adversary needs to guess about the key. When Hk = 0, the adversary knows the key explicitly and the communication is not secure. • Solution: Use a series of dynamic secrets, i.e., updates between t0 and t1 • Rationale: Secrecy replenished as the attacker cannot constantly overhear perfectly

8. Secret Safety Model No dynamic secrets Dynamic secrets, i.e.,

9. Advantage of Dynamic Secret • Information loss is not recoverable by any computational effort • Information loss can be accumulated

10. Outline • Problem statement • Overview • Dynamic secrets • Extraction • Collection • Amplification • System secret protection • Bootstrapping security and implementation • Summary and conclusion

11. Extracting Dynamic Secrets • Key ideas • Monitor retransmissions • Sender and receiver agree on set of frames • Hash such frames into dynamic secrets • One Time Frame (OTF) is refers to a frame that is only aired once and correctly received.

12. AET Algorithms

13. Example: Stop-n-Wait

14. Collecting Dynamic Secrets • Maintain a set of frames ψ • Initially ψs = ψr = Ø • Remarks • ψs and ψr differ of at most 1 frame • The reception of a new frame ensures ψs = ψr

15. Collecting Dynamic Secrets • Maintain a set of frames ψ • Initially ψs = ψr = Ø • Remarks • ψs and ψr differ of at most 1 frame • The reception of a new frame ensures ψs = ψr ψ

16. Amplifying Attacker’s Entropy • Goal: Increase attacker’s uncertainty • Input: ψ set • Output: A secret S with high entropy • Denoted as S = F(ψ)

17. Amplifying Attacker’s Entropy • Random hashing theory • uniform-randomly choosing a function from a universal-2 hashing class • The expected hash output distribution will be close to the uniform distribution when the output is sufficiently short [1] - J.L. Carter and M. N. Wegman. Universal classes of hash functions. Journal of Computer and System Sciences, 18:396-407, 1979

18. Amplifying Attacker’s Entropy • Entropy amplification • If  Attacker has < 1 bit info about S • If  Uncertainty bounded by ϵ - 1 [2] – Alfred Rényi. On measures of information and entropy. In Proceedings of the 4° Berkeley Symposium on Mathematics, Statistics and Probability, 1960

19. Dynamic Secret Generation • The above discussion justifies the use of the following method • Collect OTFs until | ψ | > nts • Agree on a randomly chosen universal-2 hash function F • Generate S(t) = F(ψ) • Reset ψ = Ø

20. Outline • Problem statement • Overview • Dynamic secrets • Extraction • Collection • Amplification • System secret protection • Bootstrapping security and implementation • Summary and conclusion

21. System Secret Protection • At secret generation • Divide s(t) = u(t) || v(t) • To protect the privatepublickey pair and secret symmetric key respectively • Remark: information loss will accumulate • Entropy is non decreasing

22. System Secret Protection

23. Outline • Problem statement • Overview • Dynamic secrets • Extraction • Collection • Amplification • System secret protection • Bootstrapping security and implementation • Summary and conclusion

24. Bootstrapping Security • Scenario: Use time to invest in security • Solution: the sender transmits random data at first to build up security

25. Prototype Implementation • 802.11g Extracting dynamic secrets at receiver Hash Extracting dynamic secrets at sender

26. Outline • Problem statement • Overview • Dynamic secrets • Extraction • Collection • Amplification • System secret protection • Bootstrapping security and implementation • Summary and conclusion

27. Summary and conclusion • Our work strengthens security in the case of secrecy leakages by using dynamic secrets • For future work, use prototype for experimental evaluation