Digital Steganography

Digital Steganography is the practice of concealing a computer file, message, image, or video within another file, message, image, or video. Although the earliest recorded use of this practice in physical media dates back to 440 BCE in Greece, the methodology became mainstream during the wars of the 21st century. For intelligence agencies, the advantage of steganography over cryptography is that the secret message itself does not attract attention. Messages that are clearly encrypted, no matter their sophistication, inspire efforts to crack them. Where encryption focuses on protecting the contents of a message, steganography is concerned with concealing the fact that a secret message is being sent in the first place.
In digital steganography, messages and images are hidden inside of a transport layer, such as document files, audio files, and image files. These media files are popular with intelligence agents because of their large size. For example, a steganographic message might start with an image file of a cat making a silly face and adjust the color of every hundredth pixel to correspond to a letter in the alphabet. The change is so subtle, and the methodology of hiding messages so diverse, that it is virtually impossible to detect unless someone was already looking.
Examples include:

• Concealing messages within the lowest bits of noisy images or extreme decibels in sound files.
• Pictures embedded in video material
• Modifying the echo of a sound file

Intelligence Agencies often used social media platforms to send their messages, as the nature of viral material and memes usually meant that soldiers in both armies could be counted on to share and spread the transport media themselves. Different units could be assigned different forms of viral material, ranging from cringe videos to captioned images of popular shows, with set methods of hiding and finding messages known only to them. For this reason, many intelligence agencies became skeptical of sudden boosts in meme format popularity, as these surges could be signs of steganographic messages being transmitted.

Audio analyzed through a spectrogram, revealing a hidden image

[Skimel, CC BY-SA 4.0 , via Wikimedia Commons]