22-06-2012, 01:04 PM
Image Steganography and Steganalysis
Steganography
Steganography - “covered writing”.
For example (sent by a German spy during World War I),
Apparently neutral's protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on byproducts, ejecting suets and vegetable oils.
Ancient Steganography
Herodotus recounts the story of Histaiaeus, who wanted to encourage Aristagoras of Miletus to revolt against the Persian king. In order to securely convey his plan, Histaiaeus shaved the head of his messenger, wrote the message on his scalp, and then waited for the hair to regrow. The messenger, apparently carrying nothing contentious, could travel freely. Arriving at his destination, he shaved his head and pointed it at the recipient.
Active and Passive Warden Steganography
Wendy can be passive:
Examines all messages between Alice and Bob.
Does not change any message
For Alice and Bob to communicate, Stego-object should be indistinguishable from cover-object.
Wendy can be active:
Deliberately modifies messages by a little to thwart any hidden communication.
Steganography against active warden is difficult.
Robust media watermarks provide a potential way for steganography in presence of active warden.
Steganalysis
Steganalysis refers to the art and science of discrimination between stego-objects and cover-objects.
Steganalysis needs to be done without any knowledge of secret key used for embedding and maybe even the embedding algorithm.
However, message does not have to be gleaned. Just its presence detected.
Steganography, Data Hiding and Watermarking
Steganography is a special case of data hiding.
Data hiding in general need not be steganography. Example – Media Bridge.
It is not the same as watermarking.
Watermarking has a malicious adversary who may try to remove, invalidate, forge watermark.
In Steganography, main goal is to escape detection from Wendy.