INVITATION TO CYBERSECURITY 178 ing parties to transmit information in an open channel without onlookers noticing. The only necessary and sufficient condition is that the communicating parties have access to a shared resource that at least one of them can modify—this allows for one-way communication. If multiple parties can modify the shared resource, then multi-way communication can take place. In steganography, the information is not scrambled, like in cryptography, instead it is “covered.” A simple example of steganography is an acrostic—a message where the first letter of every word or line spells out a word or phrase. This is common in poetry, like in the poem, “A Boat Beneath a Sunny Sky” where the first letter of every line spells out the full name of the real-life inspiration for the character, Alice. As another example, even if the following battlefield correspondence was intercepted by enemy forces, they would find it unworthy of any serious attention. However, it contains a top-secret hidden message: ATTN: THE TROOPS ARE COOKING KABOBS AT THE DOCKS AT WEDNESDAY NOON A classic example of steganography from real life was carried out by Vietnam prisoner of war, and later United States Senator, Jeremiah Denton. He was held by the North Vietnamese, and they forced him to participate in a propaganda interview praising the North Vietnamese’s treatment of prisoners so they could televise it to the world and “prove” that they were abiding by international humanitarian law. Denton did say the words they gave him for the video camera, but while he was doing so he was also blinking his eyes to communicate in Morse code the word TORTURE to describe what was actually going on in the prisons (see Figure 7.15). The North Vietnamese did not detect the covered message, and they released the video. For those with eyes to see it, like the United States Naval Intelligence, the real message got through. Figure 7.15 Prisoner of war Jeremiah Denton saying all the right words while blinking the word TORTURE in Morse code.
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