Authenticated communication through insecure channel using visual channel
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Transcript of Authenticated communication through insecure channel using visual channel
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AUTHENTICATED COMMUNICATION THROUGH INSECURE CHANNEL USING VISUAL CHANNEL
Cheh Carmen
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OVERVIEW Introduction
Protocol Project
Design Issues Existing barcodes and algorithms Proposed barcode and analysis Future development
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INTRODUCTION Computers located in many public
places Use of public computers is plagued with
many security problems
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PROTOCOL Visual channel
Visual Channel
visual inspection
Server
Mobile Device equipped with camera
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A-101-30-003
K-354-90-981
C-000-05-011
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PROJECT Implement 2D barcode Two criteria
u ( vw , kb ) = c d ( vw , vo ) < δ
Proof-of-concept
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DESIGN ISSUES(1) Choosing an image Color, gray-scale or binary?
Binary
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TYPE OF IMAGE Picture or barcode?
Barcode One barcode or multiple?
Multiple Visual cue
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DESIGN ISSUES(3) Digital watermark Fragile or robust?
Fragile Spatial domain or frequency domain?
Spatial domain Edge pixel hiding or block data hiding?
Block data hiding
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ANALYSIS OF BARCODES L-shaped barcode
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ANALYSIS OF L-BARCODE High data embedding capacity =2/3 Not very secure
Key space = 4!x4! Quite poor image quality
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PROPERTIES OF BARCODE High data capacity Moderate image quality High security
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PROPOSED ALGORITHM 1 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
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ALGORITHM 1 (CONT.) 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
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ALGORITHM 1(CONT.) 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
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ALGORITHM 1(CONT.) 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
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ALGORITHM 1(CONT.) 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
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ALGORITHM 1(CONT.) 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.
0 0 1 0 1 0 1 0 0
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ALGORITHM 1(CONT.)
F’’ = 0 1 0 0 1 0 1 1 0 Current RCL = 2 b1b2 Ξ 0 mod 4
Result : 0 0 0 1 1 0 1 1 0
INVARIANT: RCL F’’ Ξ b1b2 mod 4
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ALGORITHM 1(CONT.) 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
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ALGORITHM 1(DECODING) 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
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ALGORITHM 1(DECODING) 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
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ALGORITHM 1(DECODING) Fw’’ = 0 0 0 1 1 0 1 0
b0 = 0 b1b2 = 4 mod 4 = 0 B = b0b1b2 = 000
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ANALYSIS OF ALGORITHM 1 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
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ALGORITHM 2 Example: F=3 bits B=2 bits
Divide F into 4 cosets
Entries in table represent all possible F Header represents all possible B
0 1 2 3000 001 010 011111 110 101 100
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ALGORITHM 2(CONT.)
F = 000 B = 11
F belongs to coset 0. Move to coset 112=3 100 Modify F to 100
0 1 2 3000 001 010 011111 110 101 100
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ALGORITHM 2(CONT.) In general, F = n bits, B = n-1 bits Partition F into 2n-1 cosets Each coset has 2 elements Choose codeword in coset B s.t. d(F,c)
is minimum among all other codewords in coset B
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ANALYSIS OF ALGORITHM 2 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
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FUTURE DEVELOPMENT Compromising a bit of embedding
capacity for visual effect Experimenting with different kind of
distance formula Qgram Edit distance
Simulation
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