mimo transmissions with information theoretic secrecy for secret key agreement in wireless networks
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MIMO Transmissions with Information Theoretic Secrecy for Secret-Key Agreement in Wireless Networks. Xiaohua (Edward) Li 1 and E. Paul Ratazzi 2 1 Department of Electrical and Computer Engineering State University of New York at Binghamton [email protected],

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mimo transmissions with information theoretic secrecy for secret key agreement in wireless networks

MIMO Transmissions with Information Theoretic Secrecy for Secret-Key Agreement in Wireless Networks

Xiaohua (Edward) Li1 and E. Paul Ratazzi2

1Department of Electrical and Computer Engineering

State University of New York at Binghamton

[email protected],

http://ucesp.ws.binghamton.edu/~xli

2Air Force Research Lab, AFRL/IFGB, [email protected]

MILCOM\'2005

contents
Contents
  • Introduction
  • Secure MIMO transmission scheme
  • Transmission weights design
  • Transmission secrecy
  • Simulations
  • Conclusions

MILCOM\'2005

1 introduction
1. Introduction
  • Secure wireless transmission: necessary PHY security techniques for wireless information assurance
    • Wireless transmissions have no boundary, susceptible to listening/analyzing, location, jamming
    • Wireless nodes have severe energy and bandwidth constraints  “light” techniques
    • Unreliable link and dynamic network topology

MILCOM\'2005

secure wireless transmissions
Secure Wireless Transmissions
  • Traditional secure transmission design
    • Data encryption, spread spectrum, etc
  • New idea: use antenna array diversity and array redundancy
    • A completely different approach of secure (LPI) waveform design

MILCOM\'2005

significance to cryptography
Significance to Cryptography
  • Provable (information-theoretic) secrecy
    • Inherently secure transmission, no encryption keys involved
    • Comparable to quantum cryptography
  • Provide PHY-layer LPI, and assist higher layer data encryption
    • PHY-layer assisted secret key agreement

MILCOM\'2005

secret key agreement
Secret-Key Agreement
  • Classic Shannon model
    • Alice & Bob try to exchange encryption keys for encrypted data transmission
    • Eve can acquire all (and identical) messages received by Alice or Bob
    • Perfect secrecy impractical under Shannon model
    • Computational secrecy achievable

MILCOM\'2005

phy layer transmission secrecy model
PHY-layer Transmission Secrecy Model
  • Information theoretic secrecy realizable with model different than Shannon’s
    • Eve’s channels, and thus received signals, are different from Alice’s or Bob’s
    • A reality in quantum communication, and wireless transmissions

MILCOM\'2005

information theoretic secrecy
Information-Theoretic Secrecy
  • Wyner’s wire-tap channel: secret capacity
  • Maurer’s common information concept
  • High secret channel capacity requires Eve’s channel being noisier not practical enough

MILCOM\'2005

2 secure mimo transmission scheme
2. Secure MIMO transmission scheme
  • Can we guarantee a large or in practice?
  • Possible: randomized MIMO transmission
  • Basic idea:
    • Use redundancy of antenna array
    • Exploit the limit of blind deconvolution
      • Eve can not estimate channel/symbol blindly

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transmission scheme
Transmission Scheme
  • Alice: antenna array (secure, public, pilot)
    • Does not send training signals
  • Bob: estimate symbols, no channel knowledge required

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signal model and assumptions
Signal Model and Assumptions
  • Alice, Bob & Eve do not know channels.
    • Alice estimate H by reciprocity
    • Bob need not know channel.
    • Eve depends on blind estimation.

MILCOM\'2005

mimo transmission procedure
MIMO Transmission Procedure
  • Alice select transmit antenna weights so that
  • Bob receives signal
    • By estimating received signal power, Bob can detect signals
  • Key points:
    • No channel information required for Bob, no training required  no training available to Eve
    • Redundancy in selecting weights

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3 transmission weights design
3. Transmission Weights Design
  • Existing array transmission schemes are susceptible to Eve’s blind deconvolution attack?
    • Eve can easily estimate by blind deconvolution

if with optimal transmit beamforming

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select weights with randomization
Select Weights with Randomization
  • W1(n): Redundancy in transmitting weights
  • Procedure:

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4 transmission secrecy
4. Transmission Secrecy
  • Eve’s received signal becomes

which has distribution

  • Objective: Eve can not estimate channel Hu from xe(n), which relies on
    • Assumption that Eve & Bob’s channels are sufficiently different  wireless channels fade independently when separated a fractional of wavelength
    • Unknown to Eve:

MILCOM\'2005

indeterminacy of blind symbol estimation
Indeterminacy of Blind Symbol Estimation
  • Proposition:
  • Result:
    • Eve’s error rate: high
    • Bob’s error rate: low (identical to optimal MIMO eigen-beamforming)
    • Cost paid: higher transmission power

MILCOM\'2005

transmission secrecy
Transmission secrecy
  • Weights are selected randomly and unknown to Eve, blind deconvolution is made impossible
  • Weights are selected by Alice, no need to tell Bob  equivalently one-time pad
  • Information theory guarantees high and positive secret channel capacity  provable (information theoretic) secrecy

MILCOM\'2005

eve s exhaustive search attack
Eve’s Exhaustive Search Attack
  • Eve may exhaustively try all possible channels (both ).
  • The complexity can be at least , according to quantization level Q
    • Low quantization level reduces complexity, but increases symbol estimation error  still makes high positive secret channel capacity possible
    • Example,

MILCOM\'2005

5 simulations
5. Simulations
  • BER of the proposed transmission scheme

J=6.

K=4.

QPSK.

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conclusions
Conclusions
  • Proposed a randomized MIMO transmission scheme
    • Use array redundancy and channel diversity for transmission security
    • Enhance transmission LPI in the PHY-layer by increasing the adversary’s receiving error
    • Proof of secrecy with weight randomization and limit of blind deconvolution

MILCOM\'2005

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