3. Steganography
Art of hiding information
• Initial Applications of information
hiding to Pass Secret messages.
• Histaeus used his slaves
(information tattooed on a slave’s
shaved head )
4. Cryptography
• Study of techniques for secure • German Lorenz cipher machine, used
communication in the presence of in World WarII to encrypt very-high-
third parties level general staff messages
5.
6. Cryptography(cont)
The Greeks of Classical times are said to have
known of ciphers (e.g., the scytale
transposition cipher claimed to have been
used by the Spartan military)
7. Watermarking
• Technique for inserting information into another information
(text,image,video) which can be later extracted or detected for
variety of purposes including identification and authentication
purposes
11. Characteristics of a watermark
Fragile: Distorted or broken under slight changes
Used for tamper detection.
Robust: withstand moderate to severe signal
processing attacks .
used for copyright protection and to verify
the ownership.
Semi-fragile: features of both robust and fragile.
Sensitive to modification and provides
authentication.
12. Text Watermarking
• Text-line coding
Text lines of a document
page are shifted
imperceptibly up or down
Word-shift coding Spacing
between words in a line
text is altered Character
coding
E.g., endline at the top of
a letter, say “t” is feature coding; slightly modifies the features
extended
Goal: making watermark removal more
expensive than obtaining the right to copy
from the copy right owner
16. Audio Watermarking
Spread spectrum audio watermarking (SSW)
• Narrow-band message signal is transmitted over a much larger bandwidth
So watermark is spread over many frequency bins so that the energy in one bin is
very small and certainly undetectable.
• Audio watermarks won't survive compression to a format like MP3 or WMA or
M4A, which is one reason they aren't used very much.
17. Video Watermarking
• placing a digital watermark or logo or text over an existing video in the batch
mode.
• Watermarks can be used for adding comments to your movies.
• Research is going on.
18. Applications
Tamper proofing: To find out if data was tampered.
Eg. Change meaning of images
Hidden Watermarks track
change in meaning
19. Applications
Copyright Protecton:To prove the ownership
of digital media
Eg. Cut paste of images
Hidden Watermarks represent
the copyright information
20. Applications
Quality Assessment: Degradation of Visual Quality
Loss of Visual Quality
Hidden Watermarks track change in visual quality
21. Applications
• Fingerprinting:-
Owner can embed a robust watermark that identifies the
buyer of the copy .If unauthorized copies are found later,
origin of the illegal copies can be traced.
• Authentication:-
Owner can embed fragile watermark to provide proof of
authenticity and integrity. Tampering destroys fragile
watermark and thus can be detected
22. • Ownership assertion:-
A rightful owner can retrieve a watermark from his content to
prove his ownership
23. Problems
• In case the key used during watermark is lost anyone can
read the watermark and remove it.
• In case the watermark or key is public, it can be encoded
and copyright information is lost.
