"If you want to safely hide something - leave it in plain sight." Using this method, the spies of the past were actively rewriting using invisible ink, which manifested itself only with the help of the necessary chemicals. In the digital age, this technology has an analogue - characters with the "invisibility" tag and zero width are embedded in the regular text of the messenger so that the user cannot read them without a decoder.
Researchers at Columbia University took up the concept and developed "Fontcode", a technology for encrypting data in text that works even when printed on plain paper. To do this, the encryption program translates the original message into a sequence of numbers, which are then converted into parameters for adjusting the typical font. Here the letter should be drawn by a pixel is fatter, there is a little lower than it should be, here the interval should be narrowed by a couple of pixels, etc.
For the human eye, this is the most ordinary text, but it is worth scanning it with a smartphone camera and passing it through a decoder, as we will receive a coded message. Everything works very simply, although the method has a big flaw - if you open the encoded text in a regular editor, it will simply automatically "correct" and erase all the characters. It's a shame, but on the other hand, there is automatic protection against interception of information.
The authors of the study do not work for local spies, they are enthusiastic scientists. And that's why they see the use of Fontcode in a different area - for example, this way you can implement a watermark for printing important documents. Or include in the text of the internal corporate order secret items that will be visible only to authorized employees, to protect against industrial espionage. There are many options, but most importantly, the principle of invisible ink is still relevant.