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Mobility Assisted Secret Key Generation Using Wireless Link

Signatures

Mobility Assisted Secret Key Generation Using Wireless Link

Signatures

Date： 2012.04.05Reporter : Hong Ji Wei

Auther : Junxing Zhang  Kasera, S.K.  Patwari, N.  出處 : INFOCOM, 2010 Proceedings IEEE

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Outline

INTRODUCTION1

ADVERSARY MODEL2

MOBILITY ASSISTED KEY ESTABLISHMENT33

PROTOCOL EVALUATION44

CONCLUTIONS35

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INTRODUCTION

these link signatures can be measured almost symmetrically between two ends of a wireless link.

location locking attack:the adversary steals some signature measurements it has a good chance to determine the key generated.

CIR:the channel impulse response

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the wireless link signatures at different unpredictable locations and combine these measurements to produce strong secret keys.

Using extensive measurements in both indoor and outdoor settings (i) when movement step size is larger than one foot

the measured CIRs are mostly uncorrelated (ii) more diffusion in the mobility results in less

correlation in the measured CIRs

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ADVERSARY MODEL

an adversary:that can overhear all the communication between the two devices A and B.

Assume that the adversary cannot cause a person-in-the-middle attack.

Our adversary is also not interested in causing any Denial-of-Service attacks

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MOBILITY ASSISTED KEY ESTABLISHMENT

A. Key Establishment Protocol

Phase1:SIGGEN (short for signature generation) A and B exchange SIGGEN and SIGACK

messages. Between each pair of SIGGEN and SIGACK

message exchange, A and B individually, or both move to a new location.

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Phase2:SIGCHK (short for signature check) Upon receiving the SIGCHK message from A, B

quantizes all CIR it has measured and removes any duplicates.

then encodes the remaining quantized CIRs to produce both message symbols and parity symbols.

B sends only the parity symbols to A in multiple SIGFEC (short for signature forward error correction) messages.

A quantizes the corresponding CIRs that she had measured and encodes them to produce message symbols.

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A then combines her message symbols with parity symbols she receives from B to obtain a bit stream that is identical to that of B.

In the final KEYGEN (short for key generation) phase, A and B generate a new secret key with the reconciled bit streams and verify.

To convert the bit stream obtained: utilize a key compression function(SHA-256, SHA-384, and SHA-512).

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B. Quantization and Bit Extraction Because CIRs are continuous random variables,

must quantize them in order to use them for secret key generation.

first normalize each CIR with its maximum element value.

Next, to quantize the normalized CIR to 2q discrete values with equal intervals.

simply convert integers in the resulting vector to their binary representation to extract the initial bits.

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C. Jigsaw Encoding

the simple uniform quantization cannot preserve reciprocity and even increase the discrepancy rate in quantized CIRs.

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D. RS Error Correctionadopt the RS forward error correction (FEC)

scheme

Each RS output codeword has p symbols including k input symbols followed by 2 × t parity symbols.

t :the errorcorrection capability ε:the link signature discrepancy rate.

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the computational complexity ΓEX:

1. For m = 10 and q = 5, it is larger than 2133.

2. For m = 10 and q = 1, 2, it is in the order of 2427

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PROTOCOL EVALUATIONA. Measurement Campaignwe use three mobility models: random walk ,

Levy walk, and Brownian motionLevy walk:

Brownian motion:懸浮在液體或氣體中的微粒所作的永不停息的無規則運動

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Impact of Mobility on Link Signatures

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C.Quality of Key Generation

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we use a metric called Secret Bit Rate that is defined as the average number of secret bits extracted from each channel response.

We plot the entropy values of the bit stream generated with different quantization bit numbers (per channel response).

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CONCLUTIONS

We propose an approach where wireless devices,interested in establishing a secret key.

Our results show that our scheme generates very high entropy secret bits and that too at a high bit rate.

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