Information Hiding: Introduction

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INFORMATION HIDING:
INTRODUCTION (PART2)
Dr. Shahriar Bijani
Shahed University
Sep 2014
SLIDES REFERENCES
Sanjay Goel, Watermarking &
Steganography, University at Albany, State
University of New York.
 Steganography, University of Virginia.
 Anastasios Tefas , Information Hiding
Content Verification, Dept. of Informatics,
Aristotle University of Thessaloniki.
 CS 4953, The Hidden Art of Steganography,
University of Texas at St Antonio, 2005.

2
INFORMATION HIDING SUB-DISCIPLINES

Information Hiding employs technologies from
numerous science disciplines:
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Digital Signal Processing (Images, Audio, Video)
Cryptography
Information Theory\Coding Theory
Data Compression
Human Visual/Auditory perception
Information Hiding can be classified into 4
primary sub-disciplines of Information Hiding

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Steganography
Watermarking
Covert Channels
Anonymity
COVERT CHANNELS

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Covert channels are communication paths that were
neither designed nor intended to transfer information
E.g. the telephone was designed to allow voice
communication
information could be conveyed by letting it ring a certain
number of times
 The time differences between successive phone calls could be
used
 You could use a mobile phone and call from different locations
– the street names convey the message

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Unused bits in the TCP/IP protocol headers can be used
to carry information
(Hiding data in an image, then sending that image to
someone else could also be considered a covert channel)
ANONYMITY
Anonymity is about concealing the sender and
receiver of messages
 This is the least studied sub-discipline of
information hiding

STEGANOGRAPHY

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The art and science of communicating in a way that
hides the existence of a message in some other data
Methods of transmitting secret messages through
innocuous cover carriers in such a manner that the
existence of the embedded messages is undetectable
Carriers can be audio, video, text, or any other
digitally represented code or transmission
The hidden message may be plaintext, ciphertext, or
anything that can be represented as a bit stream
6
TERMINOLOGY

The data to be hidden:
Plaintext (from cryptography)
 Secret message
 Stego-message
 Embedded data
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The data which will have a stego-message
embedded in it:
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Covertext
Cover-Object
Cover-Medium
Cover-Image\Cover-Audio\Cover-Video
Target file
TERMINOLOGY

The key used to make the stego-message secure
Stego-Key
 Secret Key
 Key

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The file with the steganography-message
embedded
Stegotext (ciphertext in cryptography)
 Stego-Object
 Stego-Medium
 Stego-Image\Stego-Audio\Stego-Video

TERMINOLOGY

Alice and Bob

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Eve, an adversary, can listen to but not modify or
forge a message
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Classical names given to the parties wishing to
communicate
passive eavesdropping
Wendy the Warden, another adversary, can
monitor, modify, or forge a message
A passive warden simply listens (like Eve)
 An active warden may modify a message
 A malicious warden may forge a fake message

INFORMATION HIDING TAXONOMY
F. A. P. Petitcolas, R. J. Anderson, M. G. Kuhn, “Information Hiding – A Survey”, Proceedings of the IEEE,
special issue on protection of multimedia content, 87(7):1062-1078, July 1999
INFORMATION HIDING TAXONOMY
Digital
Methods
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TAXONOMY
Technical
steganography uses scientific methods to hide a
message, e.g. the use of invisible ink or microdots and other
size-reduction methods.

Linguistic steganography hides the message in the carrier
in some nonobvious ways

Semagrams hide information by the use of symbols or signs.

Visual semagram uses innocent-looking or everyday physical objects to
convey a message, e.g. drawings or the positioning of items on a desk or
Website.

Text semagram hides a message by modifying the appearance of the
carrier text, e.g. delicate changes in font size or type, adding extra spaces,
or different flourishes in letters or handwritten text.
TAXONOMY

Open codes hide a message in a legitimate carrier
message in ways that are not obvious to an unsuspecting
observer.
The carrier message: overt communication,
the hidden message: covert communication.
Jargon code uses language that is understood by a group of
people but is meaningless to others.
 includes warchalking (symbols used to indicate the presence and
type of wireless network signal underground terminology, or an
innocent conversation that conveys special meaning because of
facts known only to the speakers.)
 A subset of jargon codes is cue codes, where certain prearranged
phrases convey meaning.

TAXONOMY

Covered or concealment ciphers hide a message
openly in the carrier medium so that it can be
recovered by anyone who knows the secret for how it
was concealed.

Grille cipher: employs a template that is used to cover
the carrier message.
E.g. The words that appear in the openings of the template are the
hidden message.
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Null cipher: hides the message according to some
prearranged set of rules, such as "read every fifth word" or
"look at the third character in every word."
ASPECTS OF INFORMATION-HIDING
Three different aspects in information-hiding
systems struggle with each other:
 Capacity refers to the amount of information that
can be hidden in the cover medium
 Security refers to an eavesdropper’s inability to
detect hidden information
 Robustness refers to the amount of modification
the stego medium can withstand before an
adversary can destroy hidden information.

15
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