1. Sheng Xiao, Weibo Gong and Don Towsley,2010 Infocom

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 period without 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 H k indicates how many bits the adversary needs to guess about the key. When H k = 0, the adversary knows the key explicitly and the communication is not secure.  Solution: Use a series of dynamic secrets, i.e., updates between t 0 and t 1  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 ψ s = ψ r = Ø  Remarks ψ s and ψ r differ of at most 1 frame The reception of a new frame ensures ψ s = ψ r

15. Collecting Dynamic Secrets  Maintain a set of frames ψ  Initially ψ s = ψ r = Ø  Remarks ψ s and ψ r differ of at most 1 frame The reception of a new frame ensures ψ s = ψ r 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 universal-2 hashing  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 - 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 | > n ts 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 private public key 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 Hash Extracting dynamic secrets at sender Extracting dynamic secrets at receiver

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