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2004 01 21 Presentation Steganography

May 30, 2018

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    Robert Krenn

    rkrenn@xidc.nl

    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