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Sheng Xiao, Weibo Gong and Don Towsley,2010 Infocom

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

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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

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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.

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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

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

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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

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

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

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

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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.

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AET Algorithms

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Example: Stop-n-Wait

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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

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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

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

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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: , 1979

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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

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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

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

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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

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System Secret Protection

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

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

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Prototype Implementation g Hash Extracting dynamic secrets at sender Extracting dynamic secrets at receiver

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

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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

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