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rodlette

For backup purposes, I'd like to print some encrypted secrets as QR codes.

I don't have much room for a typical printer.

Could a small thermal printer print a QR code that encodes 500-1000 bytes?

If not, anyone know of a decent, durable, low-volume alternative?

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Yes although any thermal printing I've ever done creates a print out that fades over time, so probably a horrible solution for backup codes.

Good point. Thanks!

You can get small inkjets too...

Would that happen even if you laminate it + stick it in a dark place?

The laminating process would probably blacken the entire paper

There are laminators that don't use heat ;)

Yes I found this out the hard way just last week - thought I was being pretty clever with my inside-the-box packing label.

In my experience yes. Old receipt roles fade even stored in a warehouse. I would try that anyway, as an experiment.

A cheap thermal printer for kids is around 10-20 USD (got one for such price with 10 rolls of paper, half of which is sticky paper), has bluetooth, usb and battery. Fits in a pocket. Would be fun to stick such qr code inside some not important book left lying around.

I would caution about giving children receipt paper. It may contain a lot of BPA (or replacements).

https://www.smh.com.au/business/consumer-affairs/controversi...

There are variants that claim to be long-lived, but they're in a tiny minority.

Edit: I seem to be misremembering; direct thermal transfer printers aren't available with long life prints, only thermal transfer printers are.

https://www.zebra.com/us/en/resource-library/faq/difference-...

Which is also thermal printing, but not the kind used here.

Others comment that thermal prints don't last long, but that's all dependent on the print material. The typical receipt fades after a couple of months, but Brother has small label printers that are often used in archiving and those labels can last for decades.

So just take some time to find the right medium for your needs and thermal printers can be a decent option.

One type of brother label printer (the ones that take "tze" cartridges) are thermal transfer printers, which last very well. They transfer pigment from a separate ribbon, rather than chemically change the label.

Do these require a specific software to be able to print or can they take anything and just print? Like, is it a regular driver, could I connect to this brother printer from my iPhone?

the one i've got (brother p-touch) seems to require a proprietary software suite, but i haven't really put any effort into figuring out whether there's an alternative way to print to it.

it definitely does not "just work", it's not detected as a printer in windows.

A small thermal printer would probably be direct thermal, which uses a heat head and heat sensitive coated paper. This fades away naturally, even if kept in the dark. Glue from tape will accelerate it, in case you're thinking about it to protect from abrasion.

There's also thermal transfer printers, which use a ribbon as "ink", similar to typewritter. These labels can endure much harder conditions, like scratches, high temperatures and fade. They're used all over the industry. But these aren't usually small printers and have a high cost. At that point I think you have better solutions on printing services (I understand if you don't want to have the files outside of your environment, though.)

1000 bytes is also a huge QR code. Sure, you can do it, but I'd bet that scanning it will be very hard and impossible with some apps where that usecase hasn't been tested.

I tried to find one, but failed; did find this HN comment: https://news.ycombinator.com/item?id=18498434

It says a QR code is specified as being up to 177 pixels wide (and high I presume, because square), where they can have 2 kB of data with medium error correction.

It's a bit of a chore, but manageable to do if the data is important enough. Plus, with error correction built in, you can make some mistakes.

a small laser engraver perhaps? looks like you can get one from china close to 100usd

If you need to encode 1000 bytes in a durable way, have you considered writing them by hand? Would take me about three-four minutes in each direction.

I considered just writing them, but I was concerned that I'd make a mistake, or be too lazy to do regular test decryptions/restores.

Funnily enough I'm doing something similar, but QR codes don't quite work out because their density is not enough for me (even after compression..), I've been printing using a laser printer and a software called PaperBack from the OllyDBG guy! It works surprisingly well for backing up data in paper.

You could draw it by hand; get some grid paper and a pen or marker, copy the QR code from your screen. There's plenty of error correction in a QR code that you could make some mistakes, I believe.

Thermal prints fade pretty quickly

What about one of those "pocket" photo printers?

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