2004 01 21 presentation steganography
TRANSCRIPT
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Robert Krenn
January 21, 2004
SteganographyImplementation & Detection
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Overview
What is steganography?
Implementations
Detection Defeating steganography
Conclusion Questions
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What is steganography?
Stega-
covered, from the Greek stegos or roof
-nography
writing, from the Greek graphia
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What is steganography?
The art of hiding information inside information
Since everyone can read, encoding text
in neutral sentences is doubtfully effective
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What is steganography?
The art of hiding information inside information
Since everyone can read, encoding text
in neutral sentences is doubtfully effective
SinceEveryoneCanRead, EncodingText
InNeutralSentencesIsDoubtfullyEffective
Secret inside
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What is steganography?
What is it used for?
Hiding the fact that you are sending messages
Hiding several messages inside data Digital watermarking
Kerckhoffs' principle Secure with knowlegde of the system
Message can only be read with secret key
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What is steganography?
Hiding several messages
Deniable cryptography
Knowledge of encrypted data No proof of how much information is stored
Rubberhose (http://www.rubberhose.org)
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What is steganography?
Digital watermarking
Not really hiding information
Important: not modificable Uses the hiding-property of steganography
Recent: MPAA hides watermarks in movies
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Implementation
Hiding information
Text / Webpages
Images Audio
Video
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Implementation
Text / Webpages
Use of a codebook
Layout of texts Every Nth character
Use of whitespaces and newlines
Can be difficult to detect and decode
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Implementation
Text / Webpages
In the midway of this our mortal life,
I found me in a gloomy wood, astrayGone from the path direct: and e'en to tellIt were no easy task, how savage wildThat forest, how robust and rough its growth,Which to remember only, my dismayRenews, in bitterness not far from death.Yet to discourse of what there good befell,All else will I relate discover'd there.How first I enter'd it I scarce can say
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Implementation
Text / Webpages
In the midway of this our mortal life,
I found me in a gloomy wood, astrayGone from the path direct: and e'en to tellIt were no easy task, how savage wildThat forest, how robust and rough its growth,Which to remember only, my dismayRenews, in bitterness not far from death.Yet to discourse of what there good befell,All else will I relate discover'd there.How first I enter'd it I scarce can say
06081913030629170827 meet at dawn
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Implementation
Images
Cover image
Identify redundant data Replace (a subset of) redundant bits with data
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Implementation
Images
JPEG uses discrete cosine transformations (DCT)
Transform pixel blocks to DCT coefficients Get least significant bit of each DCT coefficient
Replace LSB with secret message bit
Insert modified DCT into output image
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Implementation
Images
Original image Data embedded inside
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Implementation
Images
JPEG stegencryption
Operates in transformation space No visual changes
GIF and BMP stegencryption
Operates in low bit planes Subject to visual attacks
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Implementation
Images
Original image Data embedded inside
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Implementation
Audio
Use frequencies inaudible to humans
Embed data using the LSB
Encoding musical tones
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Implementation
Video
Visible signals (gestures, movements)
Same techniques as with images
Same techniques as with audio
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Detection
Text
Look for (disturbings of) patterns
Odd use of language
Line heights and whitespaces
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Detection
Images
Examine color palette
Size of the image
Differences:
Format Last modifieddate
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Detection
Images
Apply filters to steganograms
Visible representation of statistical data
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Detection
Filtered
Original image Embedded data
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Detection
Filtered
Original image Embedded data
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Detection
Audio
Statistical analysis
Analyze patterns in background noise
Distortions
Measure inaudible frequencies
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Detection
Video
Look for distinguishing movements
Same techniques as with images
Same techniques as with audio
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Defeating steganography
Text
Change spacing, interpunction
Modify line heights, layout
Add or remove words
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Defeating steganography
Images
Compress with lossy compression
Convert to different format
Resize the image
Modify colors
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Defeating steganography
Audio
Compress with lossy compression
Change bitrate
Alter / limit frequency spectrum
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Defeating steganography
Video
Same techniques as with images
Same techniques as with audio
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Conclusion
Hide data practically everywhere
Detection of steganography
Possible, but can be difficult
Hard when valid to Kerckhoffs' principle
Defeating steganography is not hard
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Steganography
Questions?
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Steganography