The attacker compares the stego-object and the cover medium to identify the hidden message.

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

Answer: (C)

The key idea is that knowing the exact hidden message allows you to locate and extract it by comparing the stego object with the original cover. In a known-message attack, the attacker already knows the payload that was embedded. By aligning the stego with the cover and examining where the two differ, those differences can be directly mapped to the bits of the known message. This comparison provides a straightforward route to identifying and reconstructing the hidden data because the anchor is the known plaintext itself. If the message content weren’t known, the attacker would have to rely on other, less direct detection methods. The scenario described aligns with knowing the hidden message content, hence it’s a known-message attack.