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Show HN: ShadowCat – file transfer through QR Codes in a Browser
- unprovable 5mo agoSingle 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 5mo agoInteresting idea! A demo video would be great :)
- HanClinto 5mo agoIf the phone had broken comms, how did you get the code onto the phone to run?
- Chant-I-CRW 5mo agoIn ye olden days we used cables to sync all of our apps and data to our phones.
- wongarsu 5mo agoBut why not move the data over that cable? Some kind of iOS thing that made that more complicated than pushing an app to the phone?
- rmunn 5mo agoNot OP, but I'm guessing by running the code on itself, i.e. turning the code into a QR code (or a series of them), then scanning those QR codes on the phone and reassembling them using a text-editing app on the phone.
- unprovable 5mo agoWith great difficulty...
- harkaniemi 5mo agoThis is wild. I made an identical program 24 hours ago. Mine just transfers text files
- harkaniemi 5mo agoOkei, I tested yours and it works. I would change one thing: You could start receiving chunks at any point. I had total chunk amount and chunk order in every chunk, so you can start receiving at any point.
- lukew3 5mo agoYou should turn on github pages so we can see it live. Seems cool but I’m not at my pc rn
- hootz 5mo agoI 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 5mo ago> a convoluted mess of audio frequency modulation Like a modem
- hootz 5mo agoI 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!
- skinfaxi 5mo agoDid you explore using frequencies outside the range of human hearing?
- hootz 5mo agoNo, but that's a cool idea. I think the main problem is that consumer hardware usually gets kinda inconsistent outside our hearing range.
- deletedie 5mo agoApple uses this approach when pairing some devices for verification e.g. setting up HomePods using an iPhone
- reaperducer 5mo agoDid you explore using frequencies outside the range of human hearing? Amazon had modems very much like this in its little buttons that you could stick to your refrigerator and automatically order different items. When setting up the device, you could only hear the little clicks as it turned on and off. I loved the technology. Hated that the prices changed all the time and you never knew what price you were going to pay ahead of time.
- villgax 5mo agoWhat 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 5mo agoI 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?
- bensyverson 5mo agoI've done a POC with the native QR reading code on iOS. The short answer is: it's not a problem at all, and you can drive very large QR codes for more efficient transfer.
- rirze 5mo agoYou could also do it the menial way; create multiple QR codes that can connect together. Not very practical for everyone except the very-motivated.
- 0cf8612b2e1e 5mo agoWhy not record with a standard high quality webcam and do the QR processing later? That’s how I would exfiltrate a large volume of data.
- anhldbk 5mo agoI also implemented a static web with that idea: https://github.com/anhldbk/get-beam https://github.com/anhldbk/get-beam
- tripflag 5mo agoCool! 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.
- thedougd 5mo agoI'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.
- skinfaxi 5mo agoIf you can connect to Github pages couldn't you exfil that way? This takes 2 mins for 100KB.
- thedougd 5mo agoNot quietly. Uploads are commonly monitored by data loss prevention (DLP) solutions, especially when MITM is being used for corporate proxy. Downloading a tiny JS from a CDN, or accessing a GitHub page is mostly noise, especially if obfuscated well.
- skeptic_ai 5mo agoNpm install qr-made-up-name Can show qr in console. How do you stop that?
- thedougd 5mo agoI'm likely being overly specific, but blocking npm downloads, installation on corporate devices, etc is trivial in a restrictive corporate environment.
- MattCruikshank 5mo agoI'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.
- skinfaxi 5mo ago> 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. Why do you need a separate device for this and not just an airgapped computer?
- MattCruikshank 5mo agoMe, in my life, I have a PC that's connected to the internet. I have a phone that's connected to the internet. I want another device, which I imagine to be a Pi or Esp32 or something with a camera and a touchscreen display, and capacitive charging. After I program it and give it the public/private keypair and the OTP, I imagine physically breaking off a USB port, or sealing one with some hardening resin. I don't want an entire airgapped computer. Maybe you do, that's fine. For me, I'd love it to be a credit-card sized doodad.
- deleted 5mo ago[deleted]
- reaperducer 5mo agoI 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. Congratulations. You just invented IrDA: https://en.wikipedia.org/wiki/IrDA https://en.wikipedia.org/wiki/IrDA
- alex_suzuki 5mo agoCool stuff. I’m fond of the “single HTML file” deployment option.
- unprovable 5mo agoCheers!
- MarStudio 5mo ago[dead]
- divan 5mo agoThis method of animated QR data transfer is quite efficient with fountain codes. I had PoC implementation back in the day - Txqr [1] [2] [1] https://divan.dev/posts/animatedqr/ https://divan.dev/posts/animatedqr/ [2] https://divan.dev/posts/fountaincodes/ https://divan.dev/posts/fountaincodes/ Recently I rewrote it in Dart/Flutter and finally implemented RaptorQ codes (way more efficient than Luby used in original Txqr). Testing it internally now, prepareing Appstores/GooglePlay/Web deployment and new article.
- fizza_pizza 5mo ago[flagged]
- acrophiliac 5mo agoWhat's the length limit? I tried pasting some text and got this message: code length overflow. (85700>18672)
- unprovable 5mo agoQR code has limits, use the file transfer to chunk it. :)
- Levitating 5mo agohttps://gist.github.com/SMUsamaShah/fd6e275e44009b72f64d0570256bb3b2 https://gist.github.com/SMUsamaShah/fd6e275e44009b72f64d0570...
- aliirz 5mo agovery nice list! Can I suggest adding my https://phntm.sh https://phntm.sh as well? itis a zero-knowledge file transmission system.
- Levitating 5mo agoI am not the author, you could leave a comment on the gist instead.
- Aleesha_hacker 5mo agoLet Ai help you research not write keeps the content human and original
- zerocloudpdf 5mo ago[flagged]
- jaysyrk 5mo agoI created a file optimizer, one single file. I was wondering if i could work with you to integrate that into your project. Lmk!!
- HozefaKanchwala 5mo ago[flagged]
- encom 5mo agoWe used to be able to send arbitrary files between phones using Bluetooth. Where did that go? We had a bit of a music piracy ring going at school for a time. Good times.
- kig 5mo agoThis is cool and minimalistic! I've been noodling on https://qr-send.com https://qr-send.com which is a slightly more polished version of the "erasure fountain codes + stream of QRs"-idea, inspired by divan's Txqr posts but using Wirehair FEC for the fountain code (basically: you receive ~file size bytes via QR codes and it magically assembles them into the source file regardless of missed codes). It's an offline-first progressive web app and there are native & wasm builds for the sender. The browser-to-browser transfer falls up to WebRTC when possible because 30 MB/s over wifi beats a 100 kB/s QR stream. The QR scanner is a heavily-optimized WASM build of zbar, scanning at 60 fps on mobile & multiple QRs per frame (but it's finicky! Work in progress.)
- cl3misch 5mo agoThat sounds amazing! The WebRTC "fallback" basically means the QR code is just a handshake when both devices are on the same network?
- kig 5mo agoThe handshake details are passed alongside the data so that if a direct connection is successful, the network races the optical transfer.
- dschep 5mo agoThis looks like a nice polished implementation of the idea, but when I try and use it, I get to "file complete" but then.. nothing? And I see no way to report a problem or bug.
- dsewell2707 5mo ago[flagged]
- m_m_carvalho 5mo agoClever use of QR for file transfer. How does it handle larger files? Is there chunking + reassembly on the receiving end?
- econ 5mo agoFinally real one way data transfer.
- MeherunJessi 5mo ago[dead]
- okandship 5mo agoanimated qr + erasure coding is a neat fit here. the interesting ux question is how clearly the receiver shows progress and recovery
- unprovable 5mo agoThere is a toggle where you can show what chunks have been received. This is also where the 'show specific chunk' function comes in... the receiver can see "oh, I'm only missing chunk 125, so just show me that" etc. etc.
- davidcollantes 5mo agoIs there a client that needs to be used to be able to receive files this way? I tried the dedicated QR reader on my iPhone, and the Camera app, and couldn’t get it to assemble the chunks. It will show the encodings one after the other, but nothing else.
- teravor 5mo agoi feel like it should be possible to push this to extremely high bandwidth. use a 1D code variant with very high FPS to work around the rolling shutter.
- msafi04 5mo agoI love the focus on giving a second life to old hardware. We often talk about 'local-first' for privacy, but this shows how local-first is also great for hardware longevity. It’s refreshing to see a tool that doesn't require a cloud connection or a functional Bluetooth stack to be useful.
- TimoKn 5mo ago[flagged]
- unprovable 5mo agoUpdate - put it on a site for folk to use: https://shadowcat.online/ https://shadowcat.online/