Transcript YASS: Yet Another Steganographic Sceme that Resists Blind

YASS:YET ANOTHER
STEGANOGRAPHIC SCHEME
THAT RESISTS BLIND
STEGANALYSIS
Solanki et. Al
Presented by Yamin Noor
STEGANOGRAPHY - HISTORICAL NOTES
 Demaratus sent a warning about a forthcoming attack to Greece by
writing it directly on the wooden backing of a wax tablet before
applying its beeswax surface.
 Histiaeus shaved the head of his most trusted slave and tattooed a
message on it. After his hair had grown the message was hidden. The
purpose was to instigate a revolt against the Persians.
STEGANOGRAPHY - NOW
 Used for secured communication of secret message.
 Hidden in digital images (host/cover).
 Hidden message cannot be detected by statistical or perceptual analysis
of Stego/Composite image.
 Must be recoverable by receiver even after distortion.
EXAMPLE OF STEGANOGRAPHY
EXAMPLE OF STEGANOGRAPHY
DIGITAL IMAGE STEGANOGRAPHY
 JPEG is the most popular format.
 Most methods hide data in the LSB of the quantized DCT coefficients of
the image.
 Hiding image in specific region or the whole image changes the
histogram of DCT coefficient.
 Steganalyzers can compare the histogram of DCT coefficients of the
host and the stego.
 Good steganography should yield stego with DCT coefficent histogram
closest to that of the host.
BLIND STEGANALYSIS
 Unavailability of the host image.
 Approximate host image from the stego (self-calibration).
 Better steganography need to be able to resist self-calibration.
 Authors claimed that YASS can resist self-calibration and, thereby, resist
blind steganlysis.
RECAP
 There will be difference in features between host and stego.
 Steganlysists need host image or a good approximate of host image to
find such differences.
 Resisting the steganlysists from approximating the host image makes the
steganography undecodable.
YASS
 Implements randomized hiding of data.
 No consistent assumption about the hiding process can be made.
 Host image features cannot be reliably estimated.
IMPLEMENTATION OF YASS
Image (MxN)
N
M
IMPLEMENTATION OF YASS
Image (MxN)
N
M
Big Blocks (BxB)
B
B
IMPLEMENTATION OF YASS
Image (MxN)
N
M
Big Blocks (BxB)
8x8
8x8
Randomized Small
Block (8x8)
8x8
8x8
B
B
IMPLEMENTATION OF YASS
Image (MxN)
N
M
Big Blocks (BxB)
8x8
8x8
Randomized Small
Block (8x8)
DCT of Small Block
Embed data in nonzero Coefficients
8x8
8x8
B
B
IMPLEMENTATION OF YASS
Image (MxN)
N
M
Big Blocks (BxB)
Randomized Small
Block (8x8)
DCT of Small Block
Embed data in nonzero Coefficients
B
B
IMPLEMENTATION OF YASS
Image (MxN)
N
M
Big Blocks (BxB)
Randomized Small
Block (8x8)
DCT of Small Block
Embed data in nonzero Coefficients
Reconstruct Image
B
B
REPEAT-ACCUMULATE CODE
 JPEG Compression can cause erroneous decoding by the receiver.
 Repeat-Accumulate Code is an algorithm that can reduce error during
JPEG compression through an iterative algorithm.
PERFORMANCE OF YASS
 Embedding Capacity
 Detection probability
EMBEDDING RATE
 Embedding rate or capacity is the number of bits that can be hidden in
an host using a steganographic algorithm.
 Embedding rate of YASS depends on
 JPEG Quantizer Factors QFa and QFh
 Dimension of Big Block Size B
JPEG QUANTIZER FACTORS
DIMENSION OF B
DETECTION OF YASS
 Training a support vector machine (SVM)
 Xo = Actual Host Image
 X1 = Actual Stego Image
 Yo = Observed Host Image
 Y1 = Observed Stego Image
DETECTION OF YASS
 Farid – 72 dimensional vector based
 PF-23 – 23 dimensional DCT based
 PF-274 – 274 dimensional DCT and Markov based
 DCT Histogram – Histogram of DCT Coeff
 Xuan-39 – Spatial domain steganalysis
 Chen-234 – JPEG Steganlysis
DETECTION OF YAS
QFa - QFh
QFa - QFh
TRADE-OFFS IN YASS
Embedding Capacity
Steganalysis Performance
Big Block Dimension
Big Block Dimension
TRADE-OFFS IN YASS
Embedding Capacity
Steganalysis Performance
YASS VS. OTHER STEGANOGRAPHY
CONCLUSION
 YASS provides more security than other methods against blind
steganlysis.
 Randomly chosen blocks confuses staganlysists and reduces the
consistency of steganlysis algorithm.
 There is a real-estate cost for YASS, i.e. the number of bits that can be
stored is less than other methods.
QUESTIONS