文档介绍：Applications of Data Hiding in Digital Images
自動化資訊處理實驗室
報告人:李惠龍
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Outline
Introduction
Difference between cryptography and steganography
Applications
Covert communication
Digital watermarking
Watermarking for tamper detection and authentication
Our application
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Steganography
The art of concealed communication
Hiding of secret messages within another message (or carrier)
Make info. imperceptible
Keep existence of info. secret
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Difference between cryptography and steganography
Cryptography: Protect the content of messages
Scramble data such that it is unreadable
Ciphertext attracts attackers for decryption
Steganography: Conceal the existence of messages
Hide data in another data
Hide the existence of communication
Stegotext minimizes attackers’ interest
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Difference between cryptography and steganography
A secure crypto-system
One in which an adversary who understands the system, but does not know the key, can not recover the data
A secure stego-system
One where an adversary who understands the system, but does not know the key, can obtain no evidence that a communication has taken place
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Robustness
The ability to extract hidden information after common image processing operations:
linear and nonlinear filters, lossy compression, contrast adjustment, recoloring,
resampling, scaling, rotation, noise adding, cropping, printing / copying / scanning, D/A
and A/D conversion, pixel permutation in small neighborhood, color quantization (as in
palette images), skipping rows / columns, adding rows / columns, frame swapping,
frame averaging (temporal averaging), etc.
Undetectability
Impossibility to prove the presence of a hidden message. This concept is inherently
tied to the statistical model of the carrier image. The ability to detect the presence does
not automatically imply the ability to read the hidden message. Undetectability should
not be mistaken for invisibility  a concept related to human perception.
Invisibility
Perceptual t