Hide a note inside ordinary text GLYPH

Obfuscation, not encryption, and the difference matters

The page says this above the controls and it is worth saying again with the reason. The note is hidden in characters that have no width (zero-width space, zero-width non-joiner, zero-width joiner, word joiner) sitting between the letters of ordinary text. A reader sees nothing unusual. A machine sees them immediately: any tool that lists code points shows them at once, and UNSEEN, on this site, exists to find exactly this.

So this hides a note from a person glancing at the text. It hides nothing from anybody who thinks to look, and it protects nothing from anybody who does. If the contents need to be secret rather than inconspicuous, encrypt them: CAPSULE makes a file only the holder of a passphrase can open, and hiding an encrypted string with this is a reasonable thing to do where the two jobs are genuinely separate.

What removes it, usually by accident

• Retyping. Anybody who reads the text and types it out again produces a clean copy.
• A screenshot, or OCR. A picture of text has no characters in it.
• Platforms that normalise. A good many chat applications, content management systems, ticketing tools and mail clients strip invisible characters as a matter of course, without telling anybody.
• Copying through something that reflows the text, such as pasting into a plain-text field with normalisation on.

Which means a note that does not come back is not evidence of anything. It is at least as likely the carrier text went through something tidy as that somebody stripped it deliberately.

What it is reasonably used for

Marking which copy of a document went to whom, so a leak can be traced to a copy; CANARY is the version built for that, with a recipient ledger and the limits set out. Carrying a short reference alongside text in a system that has nowhere to put one. And demonstrating the technique to people who need to know their text can carry things they cannot see, which is the reason UNSEEN exists.

It is not reasonably used for hiding anything from an adversary. Assume a determined reader finds it, because they will.