OutlineSteganography LSB SteganographyLSB Steganalysis
CryptographyCryptography scrambles a message to obscure its meaning.Today secure communication is often identified with cryptography.However, cryptography reveals the fact that communication is happening.???@2*$#d(*%7*
SteganographyThe word steganography comes from Greek, steganos and graphein.Steganography is the art of hiding information in ordinary-looking objects.Steganography aims to conceal the existence of secret communication.
Classical SteganographyExamples:Hidden tattoo, Covered writing,Invisible ink, Microdots, Character arrangement, Paper mask,etc.Hiding a secret message in physical objects.Secrecy depends on keeping the methods secret.
Modern SteganographyHiding information in digital objects, Invisibly.The Invisibility must depend on just the stego-key, not the stego system.
LSB SteganographyReplacing least-significant-bits (LSBs) of digital data with message bits.
Using digital multimedia, such as image, audio, video, as cover-objects.Embedding random message bits in LSBs will not cause any discernable difference from the cover-signals.Easy to implement, High payloads.11001000ExtractingEmbedding
Digital Images for SteganographyTypes of digital images: binary, gray-scale, RGB color, palette, JPEG, etc.The LSB plane of image data looks like random noise.Bit-plane decomposition of the Lena image in gray-scale.
lena.bmp6th Bit Plane4th Bit PlaneLSB Plane
LSB SteganalysisSteganalysis is the science of detecting hidden messages in digital signals.It takes advantage of statistical or perceptual distinction of stego-signals from cover-signals.LSB steganalysisVisual attack, histogram analysis (PoV analysis),Closed color analysis,Regular-singular (RS) analysis,Sample pair (SP) analysis,LR Cube analysis,Etc.
PoV analysisProposed by Westfeld and Pfizmann (IH 1999) .PoV means a pair of values which differ just in the LSBs.0 1 2 3 4 5 6 7 8 9 10 LSB embedding tends to equalize those frequencies of the values of each PoV.cover-image histogramstego-image histogramLSB Embedding
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Sample Pair AnalysisProposed by Dumitrescu et al. (IH 2003)Based on symmetry of quantized noise distribution.Take advantage of spatial correlation such as pixel adjacency.Estimate the length of hidden message.Outperform PoV analysis.cover-image histogramstego-image histogramLSB Embedding
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LR Cube AnalysisLeft and Right cube analysis (LRCA), developed by us (IH 2005)Our method uses high dim. vectors as basic units drawn from digital signals.Consider the vector noise distribution and its distortion of LSB embedding.
LR Cube AnalysisLeft cube and Right cube, and the possible cube patterns or complexities.
Cover-signals show similar complex levels between the left cubes and the right cubes, but these are not the case for stego-signals after the LSB embeddingLRCA works by measuring the similarities between these two distributions.
Center for Information Security Technologies, Korea University
Thank you
Kwang-Soo Leekslee@cist.korea.ac.kr
