The transfer carries an ordinary-looking picture with your file hidden inside it, so what lands on the other machine is an image rather than an obvious secret. It hides the file, not the transfer — and it will not survive someone who tests for steganography. Extract it again under Receive.
This device's signing key
Give this to a recipient once, and they can tell that later transfers really came from you. It signs only — it cannot decrypt anything, and it is a different key from the one under Receive. The private half never leaves this browser profile: it cannot be backed up or moved, and clearing site data destroys it.
Fingerprint
Read this aloud to the recipient. A signature only tells them the file came from whoever holds this key — comparing the fingerprint is what ties that key to you.
Pick a file, then point the receiving device's camera at the code. The stream repeats forever — there is no need to catch every frame, or to start the camera before the sender.
Point the camera at the sending screen and hold steady. Frames you miss are recovered automatically, so partial coverage is fine.
This device's key
Give this to a sender and they can encrypt to you without either of you agreeing a passphrase first. The private half never leaves this browser profile — it cannot be backed up or moved, and clearing site data destroys it.
Fingerprint
Read this aloud and have the sender check it matches what their screen shows. Without that step, anyone who substituted their own key in transit can read the file.
Signed by
Extract a hidden file from an image
For a picture that was sent with Hide the file inside an image ticked. It works on any image on this device, not only one that just arrived — which is the point, since the picture is what stays on the disk afterwards. A wrong passphrase and an ordinary photograph fail the same way, on purpose.