bashalarmistalt/decimen-optical-transfer

Source: https://github.com/bashalarmistalt/decimen-optical-transfer

Decimen Optical Transfer: fountain-coded QR file transfer

Send a file between two devices using nothing but a screen and a camera. One page displays the file as an endless stream of animated QR codes; another device points its camera at it and reconstructs the file. No network path between the devices, no app, no pairing, no permissions beyond the camera. The payload travels as light.

Try it

→ decimen.app

Open it on both devices and go — nothing to install. Works offline after the first visit, and installs as an app on both iOS and Android if you want it on a home screen.

Files up to 64 MB (or a pasted text snippet), filename and media type preserved, gzip only when it helps, SHA-256 verified before anything is offered — and received video plays right in the page. Extracted from a larger experiment that reached 128 KB/s phone-to-phone.

Mid-transfer: a phone pulling a file out of the air at 130 KB/s.

Neither mode is encrypted: whatever is on the sending screen is readable by any camera pointed at it. The property this gives you is no network, not confidentiality — see privacy.

Documentation

Using it — quick start · sending · receiving · troubleshooting · install & offline · privacy

How it’s built — architecture · protocol · platform quirks · build & release

The short version of the protocol: a screen-to-camera link has no back-channel, so the sender streams fountain-coded frames (Luby transform) — the receiver collects any ~K·1.15 distinct frames in any order and peels the file out. Dropped frames cost time, never correctness.

Run it yourself

npm install
npm run dev               # https dev server with HMR
npm run serve             # build, then serve the production bundle
npm run demo              # demo mode: only the bundled payloads can be sent
npm test                  # golden wire-format vectors and unit tests
npm run build             # the hosted site → dist/
npm run build:standalone  # both self-contained pages → dist-standalone/
npm run build:all         # everything

Open https://localhost:5173/send/ on the sending device and the printed Network URL on the receiving phone (accept the self-signed certificate once). Walkthrough: quick start.

Similar projects

The concept here was arrived at independently. It turns out several people have had similar ideas, and their takes are all worth a look:

• mohankumarelec/airgapped-qr-code-transfer: browser-based QR file transfer with compression and sequential chunking. Discovered after publicly demoing this project; convergent evolution in action.
• divan/txqr (2018): animated QR plus fountain codes in Go, with two excellent write-ups on why fountain coding beats sequential looping.
• sz3/libcimbar: goes past QR entirely with a custom high-density color code purpose-built for this channel.

Built by Evan Crawley (Bash Alarmist), with node-qrcode and zxing-wasm.

License

MIT