The attacker has access to the stego-object and the steganography tool or algorithm used to hide the message.

The attacker has access to the stego-object and the steganography tool or algorithm used to hide the message.

• A. Known-stego Attack
• B. Chosen-message Attack
• C. Known-cover Attack
• D. Blind Classifier attack

Answer: (B)

This question tests the attacker model in steganography: what the adversary can do with the embedding process. If the attacker can select a message and obtain a stego object that encodes that exact message using the same hiding tool or algorithm, they can study how the message is embedded and how changes in the message affect the stego object. That scenario is the essence of a chosen-message attack. So, having access to the stego object and the hiding tool means the attacker can force the system to produce stego objects for messages they choose, which is precisely what a chosen-message attack describes. The other models don’t fit as well: a known-stego or known-cover scenario involves having or relating to the original cover object, whereas a blind classifier attack centers on detecting steganography without relying on embedding tools or chosen messages.

This question tests the attacker model in steganography: what the adversary can do with the embedding process. If the attacker can select a message and obtain a stego object that encodes that exact message using the same hiding tool or algorithm, they can study how the message is embedded and how changes in the message affect the stego object. That scenario is the essence of a chosen-message attack.

So, having access to the stego object and the hiding tool means the attacker can force the system to produce stego objects for messages they choose, which is precisely what a chosen-message attack describes. The other models don’t fit as well: a known-stego or known-cover scenario involves having or relating to the original cover object, whereas a blind classifier attack centers on detecting steganography without relying on embedding tools or chosen messages.