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Authenticated communication through insecure channel using visual channel

Cheh Carmen. Authenticated communication through insecure channel using visual channel. Introduction Protocol Project Design Issues Existing barcodes and algorithms Proposed barcode and analysis Future development. overview. Computers located in many public places

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Authenticated communication through insecure channel using visual channel

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  1. Cheh Carmen Authenticated communication through insecure channel using visual channel

  2. Introduction • Protocol • Project • Design Issues • Existing barcodes and algorithms • Proposed barcode and analysis • Future development overview

  3. Computers located in many public places Use of public computers is plagued with many security problems introduction

  4. Visual channel protocol Mobile Device equipped with camera Visual Channel visual inspection Server

  5. A-101-30-003 K-354-90-981 C-000-05-011

  6. Implement 2D barcode • Two criteria • u ( vw, kb ) = c • d ( vw, vo) < δ • Proof-of-concept Project

  7. Choosing an image • Color, gray-scale or binary? • Binary Design issues(1)

  8. Picture or barcode? • Barcode • One barcode or multiple? • Multiple • Visual cue Type of image

  9. Digital watermark • Fragile or robust? • Fragile • Spatial domain or frequency domain? • Spatial domain • Edge pixel hiding or block data hiding? • Block data hiding Design issues(3)

  10. L-shaped barcode Analysis of barcodes

  11. High data embedding capacity =2/3 • Not very secure • Key space = 4!x4! • Quite poor image quality Analysis of L-barcode

  12. High data capacity Moderate image quality High security Properties of barcode

  13. F = original image (3x3 block) • Watermarking key (K,M) • K is 9-tuple : permuted coordinates of 3x3 block • M is 3x3 binary matrix : mask • B = 3-bit message : b0b1b2 • Maximum 3 bits flipped in the block Proposed algorithm 1

  14. F = 1 1 0 0 1 1 0 0 0 K =[(3,3),(3,2),(3,1),(2,3),(2,2),(2,1),(1,3),(1,2),(1,1)] M = 0 1 0 1 1 0 1 0 0 B = 0 0 0 Algorithm 1 (cont.)

  15. F XNOR M (masking F – confusion) F = 1 1 0 M = 0 1 0 0 1 1 1 1 0 0 0 0 1 0 0 Result F’: 0 1 1 0 1 0 0 1 1 Algorithm 1(Cont.)

  16. Shuffle F’ using K(diffusion) K = [(3,3),(3,2),(3,1),(2,3),(2,2),(2,1),(1,3),(1,2),(1,1)] F’ = 0 1 1 0 1 0 0 1 1 Result F’’ : 1 1 0 0 1 0 1 1 0 Algorithm 1(cont.)

  17. Invariant: MSB of F’’ = b0 B = 0 0 0 F’’ = 1 1 0 0 1 0 1 1 0 Result F’’ = 0 1 0 0 1 0 1 1 0 Algorithm 1(cont.)

  18. right-shift continuous: A binary string is right-shift continuous when MSB=LSB. right-shift continuous length: Right-shift the binary string. Right-shift continuous length is the number of digits of the same value starting from MSB without interruption by the opposite digit. Algorithm 1(cont.) 0 0 1 0 1 0 1 0 0

  19. F’’ = 0 1 0 0 1 0 1 1 0 Current RCL = 2 b1b2Ξ0 mod 4 Result : 0 0 0 1 1 0 1 1 0 Algorithm 1(cont.) INVARIANT: RCL F’’ Ξ b1b2 mod 4

  20. Modify original F Flipped bits : 1 1 0 0 1 0 1 1 0 F = 1 1 0 0 1 1 0 0 0 K = [(3,3),(3,2),(3,1),(2,3),(2,2),(2,1),(1,3),(1,2),(1,1)] Result : 1 1 0 0 1 0 0 1 1 Algorithm 1(cont.)

  21. Fw XNOR M (mask it again) Fw = 1 1 0 M = 0 1 0 0 1 0 1 1 0 0 1 1 1 0 0 Result Fw’ : 0 1 0 0 1 1 0 0 0 Algorithm 1(decoding)

  22. Shuffle Fw’ using K Fw’ = 0 1 0 0 1 1 0 0 0 K = [(3,3),(3,2),(3,1),(2,3),(2,2),(2,1),(1,3),(1,2),(1,1)] Result Fw’’: 0 0 0 1 1 0 1 0 Algorithm 1(decoding)

  23. Fw’’ = 0 0 0 1 1 0 1 0 b0 = 0 b1b2 = 4 mod 4 = 0 B = b0b1b2 = 000 Algorithm 1(decoding)

  24. Embedding capacity: 3 bits/block = 3/9 = 1/3 Average number of bit flipped/block = 2 Security: Key space = 28 x 9! Main disadvantage: Embedding capacity too low Analysis of algorithm 1

  25. Example: F=3 bits B=2 bits Divide F into 4 cosets Entries in table represent all possible F Header represents all possible B Algorithm 2

  26. F = 000 B = 11 F belongs to coset 0. Move to coset 112=3  100 Modify F to 100 Algorithm 2(cont.)

  27. In general, F = n bits, B = n-1 bits Partition F into 2n-1cosets Each coset has 2 elements Choose codeword in coset B s.t. d(F,c) is minimum among all other codewords in coset B Algorithm 2(cont.)

  28. Embedding capacity: 2 bits/block = 2/3 In general = n-1/n Average number of bits flipped = ¾ Security: Can apply M and K in the same manner as algo 1 Embedding capacity is higher than algo 1 Analysis of algorithm 2

  29. Compromising a bit of embedding capacity for visual effect • Experimenting with different kind of distance formula • Qgram • Edit distance • Simulation Future development

  30. end

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