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Show HN: ShadowCat – file transfer through QR Codes in a Browser

https://github.com/unprovable/ShadowCat
26•unprovable•2h ago

Comments

unprovable•2h ago
Single page file transfer using QR Codes and a browser. Sending device loads a file into the page, gets chunked. Receiver gets all the chunks through a camera, tosses lightly and reassembles, CRC to garnish. Designed to push data from an old phone that had broken comms after it took a swimming lesson in a coffee mug, it's been quite handy.
pajamasam•1h ago
Interesting idea! A demo video would be great :)
lukew3•1h ago
You should turn on github pages so we can see it live. Seems cool but I’m not at my pc rn
hootz•1h ago
I love this type of stuff. Some years ago I did something similar, but instead of QR Codes it used a convoluted mess of audio frequency modulation to send data through sound between devices. This is much more practical if you have two cameras.
xnx•48m ago
> a convoluted mess of audio frequency modulation

Like a modem

hootz•23m ago
I guess lmao, but much more rudimentary, less reliable and with loads of issues, as it had to blast piercing sounds through a speaker and then capture those with a microphone. But it was pretty cool when it worked!
villgax•1h ago
What would make this truly portable is being able to generate this consistently with a short prompt and generate with a local LLM. That way no network calls or file hash can prevent this
hoansdz•54m ago
I once heard someone create a QR code scanner to retrieve gigabytes of data, but the biggest problem is that cameras aren't powerful enough to handle it all. Essentially, the QR code needs to be downloaded to the device for loading; relying on the camera to retrieve it is very difficult. Am I wrong about this project? What's your solution?
anhldbk•49m ago
I also implemented a static web with that idea: https://github.com/anhldbk/get-beam
tripflag•46m ago
Cool! Out of curiosity, since qr-codes can contain binary data -- rather than base64, have you tried inserting the file as-is? That way you could do away with the ASCII separator and have a binary header as well. This would spend less frames for the same amount of data, but I'm not sure if it would be computationally cheaper. The other alternative would be the alphanumeric mode of qr-codes, but then you lose lowercase.
MattCruikshank•35m ago
I've wanted to use this for an air-gapped communication device.

I have a device with a camera and a touch-screen that only uses capacitive charging. I type a message. Bytes are encrypted. I hit send. QR codes flash on my screen. I use my PC or my normal phone to receive the encrypted bytes, and transmit them to you. You have the same device. You have your PC or phone flash encrypted QR codes. You use your device to receive, and then decrypt.

I've daydreamed about also buying several different hardware random noise generators. XOR all of their bits together. Save a huge one time pad to each of our devices. And then also use public key crypto on top of it.

I'm not really sure why I want this. But, it's my answer for how to reduce attack surface as much as possible, and have truly secret messages.

alex_suzuki•33m ago
Cool stuff. I’m fond of the “single HTML file” deployment option.
thedougd•29m ago
I've done this exact approach before. It's a good way to exfiltrate data. Post the software on GitHub pages, or a popular CDN that co-hosts other shared libraries and you've got a very difficult to block method.

Really goes to show that it's very difficult to stop a motivated and informed actor.

Show HN: ShadowCat – file transfer through QR Codes in a Browser

https://github.com/unprovable/ShadowCat
26•unprovable•2h ago•13 comments

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