Caesar Box encode
Caesar Box encode, classical cipher, a puzzle not a protection, computed on your device. Not reversible to the exact input: the text is padded with X to fill the next perfect square, and the padding is indistinguishable from real text afterwards. "HELLO WORLD" decodes back as "HELLO WORLDXXXXX".
Runs on your device. The file is never uploaded.
Caesar Box encode drops one trailing newline, then pads your text with X up to the next square number. It writes the padded text across a grid row by row and reads it back down the columns. The grid side follows from the length alone, so there is no key and nothing is hidden.
Questions
What is a Caesar box?
Your text is written into a square grid row by row, then read out column by column. Like the rail fence it is a transposition, so the letters are unchanged and only their order moves.
Why did my text come back with extra characters?
The grid has to be filled. The repository records the measured round trip: "HELLO WORLD" comes back as "HELLO WORLDXXXXX", because padding is added to complete the square and cannot be told apart from real text afterwards.
How do I decode it?
Use Caesar Box decode. It reverses the column read, then you strip any padding characters from the end yourself, since nothing in the ciphertext marks where your message stopped.
Does it hide anything?
Not from anyone looking. The grid size follows from the length of the text, so there is effectively no key to guess. Treat it as a puzzle.