Invisicoding

A‪ ​m⁨e​s⁩s⁨⁨a⁨g​e‪ ​c​o​din​g⁨ ‪s​ys​t​e‪m​ ​t⁩h‬a⁨t​ ​h‬i​de​s​ ‪a​ s‪e​c‬re​t‪ ⁩m​e​s‪s​a⁨⁨g⁨e‬⁨ ​i⁩n​ ⁩p‬l⁣a⁩i‪n⁩⁣ text by embedding invisible characters in between visible ones.

Example: Encoder / Decoder

Why?

A‪⁩f⁩t⁨⁨er⁨ ‬g​et​t⁩i​n⁨g⁩ ​t⁨r⁨i‬pp⁣e​d​ ⁨u‪p​ b​y​ ‬​a‬n‪ ‬i⁨n⁨v​i⁩s​ib​l​⁣e​ ‬⁣c​h⁩a​ra​c​t​e​r⁨ ​i⁩n⁨⁨ a​ ​b⁨⁨a‬s​h ⁨c⁨o⁩m​ma⁨nd​ ⁨a‬t‬ w⁣o​r‬k‪,​ ⁨⁨I‬ ​e‬⁣n​d⁩e⁨⁨d⁨ ​up⁨⁨ ⁨g‬oi⁣n​g‬ ‪d‪o​w⁣n​ ​a‬ ‬r‪⁣a‪b​bi⁩t​ hole of invisible characters. I ended up discovering my issue due to a cool little website that shows the invisible characters in a block of text. Then I found a bunch of different variants and thought, how cool would it be to use these to hide a message inside regular text to pass secret messages back and forth.

How does it work?

Each character in a secret message gets translated to a two digit code that represents the ASCII character code (with an offset).

Take the secret message Hello and visible message Invisicoding.

H -> \H -> 41
e -> \e -> 70
l -> \l -> 77
l -> \l -> 77
o -> \o -> 80

The H is ASCII #72. We subtract 31 so that our valid characterset all fits within 2 digits. This ends up with 41 as our code.

We then lookup the invisible characters from a key. The key is a 10 element array of unicode character codes. For our H example, we grab key[4] + key[1].

We then alternate 1 visible character with the two invisible characters from the above mapping. Eg..

"I" + key[4] + key[1] + "n" + key[7] + key[0] + "v" + key[7] + key[7] + "i" + ...

In practice, this ends up looking like:

I‬n​vis​icoding (Working example, copy the text and go try it out for yourself!)

I made a separate debugging key using ASCII codes for the numbers 0 - 9 which helps visualize this. (See Code > Debugging for details.)

I41n70v77i77s80icoding

Here you can see the character codes embedded in the visible message.

Code

The code is pretty simple and has a few accompanying tests in src/invisicoding.js. You can build and run your own copy of the web UI with npm run start. If you make any changes to the source, you'll need to repackage it for use in browser with npm run package or npm run package-dev (the package command minifies and uglifies the output where-as package-dev does not). Or you can use the code directly in terminal:

$ node
Welcome to Node.js v17.9.0.
Type ".help" for more information.
> const { encode, decode } = require("./src/invisicoding");
undefined
> msg = encode("Hello world", "Invisicoding")
'Hello world'
> decode(msg)
'Invisicoding'

Debugging

In the source file, there is an additional key provided and commented out that swaps the invisible characters out for ASCII characters 0-9. Using this instead allows you to visualize our character codes in the text.

-- I discovered the infamous invisible character in my bash command <8 hours ago and threw this whole thing together. It currently has it's limitations. It was designed to only accept ASCII characters between 32 (space) and 126 (~). It could be extended to accept more characters by expanding to 3+ invisible characters but was out of scope for my simple demo. If you have feedback or suggestions, please open a ticket and I'd love to hear them!