4 ms·

They can’t be used to encode very much data though. They wouldn’t be suitable for storing documents, but could be used to store the location of a document. I wa

They can’t be used to encode very much data though. They wouldn’t be suitable for storing documents, but could be used to store the location of a document. I was trying to be clever once and thought I could encode X.509 certificates in QR codes. Even that much data was pushing the hard limits of what they can store, and became very hard to scan (I quickly realised this wasn’t actually very clever).

elcritch 7y ago
Can X.509 ceros use elliptic curve? They’d be much smaller.
- AmericanChopper 7y ago
  Even without the key they start to look pretty dense. You can definitely fit one in a QR code, they just start to become less reliable to scan (especially on cheap devices), and they go from looking nice to looking quite ugly. Technically most X.509 certs would have been within the limitations of QR codes (though I don’t think there is an upper bound to how large they can get), but I realized it just wasn’t fit for purpose and moved on to something else.
  - matheusmoreira 7y ago
    Are you using 8 bit encoding? An alphanumeric mode QR code containing base 64 encoded data provides less capacity. In binary mode even a 4096 bit RSA secret key fits while ECC keys produce smaller codes. The qrencode tool has an 8 bit mode but not all decoders can handle binary data. For example, my phone shows me mangled results and I can't redirect them to a file. Like structured append, it doesn't seem to have much support. I've sent patches to ZBar improving this: https://github.com/mchehab/zbar/pull/64 https://github.com/mchehab/zbar/pull/64 Hopefully it will make QR codes more useful for storing keys and other small files.
BiteCode_dev 7y ago
7kb for a supermarket bill is plenty, and you can have several of them. Forms and legal documents should all have an immutable official url and uuid anyway to point to their legal and administrative context.
- michaelt 7y ago
  The largest QR code in the standard, "version 40" - can only store 3 kilobytes at the lowest level of error correction and 1.2 kilobytes at the highest level [1]. And that's a pretty huge QR code [2] My back-of-the-envelope calculations say you'd need 61 bits per line on a receipt just to encode UPC, quantity and price. So the largest QR code would only allow 19-50 lines. And that's without including data like the store name, special offers, means of payment and so on. Believe me, plenty of people buy more than 50 items in their supermarket christmas shop :) Standardised digital receipts would be neat but, QR codes encoding the data ain't the way to go about it. [1] https://www.qrcode.com/en/about/version.html https://www.qrcode.com/en/about/version.html [2] https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg
  - smegger001 7y ago
    it could just contain a url linking to a page with to content.
  - jlgaddis 7y ago
    Seems like the obvious thing would be to have the QR code contain a "receipt ID" (UUID?) in a URL. When the QR code is scanned, the browser opens to the URL, the remote side takes your "receipt ID", and presents you with a list of all the items you purchased. I can't imagine any decent-sized retailer isn't already maintaining records like this.
    - naniwaduni 7y ago
      See, one of the useful properties of a paper receipt is that, once you receive it, you can be fairly confident about the ~one way you're going to lose it
slim 7y ago
i think datamatrix is more suitable for x509
- other_herbert 7y ago
  Yes.. I had made a form that was scanned and all the metadata for the page was stored in datamatrix at the bottom.. With a laser printer and a good scanner you can reliably put a lot of data in there...
m-p-3 7y ago
I wish we could encode PGP public keys with them, but it's still too much data. That would be a neat way of exchanging a key.
- prepend 7y ago
  How big is your pgp public key? Mine is under 4K in ascii and can definitely fit in a QR code. If you use a crypto atm it will print out your wallet’s private and sometimes public keys as QR codes.
  - AmericanChopper 7y ago
    4K is around the point where some devices will start to have issues scanning. Also, crypto wallets won’t usually give you the private key, instead they’ll give you the 12 word BIP39 seed phrase which will be around 70-80 bytes.
- StavrosK 7y ago
  You can definitely encode ed25519 keys to a QR code.
- BiteCode_dev 7y ago
  Gpg key fingerprints are very small though and can be used for that.

elcritch 7y ago

Can X.509 ceros use elliptic curve? They’d be much smaller.

AmericanChopper 7y ago
Even without the key they start to look pretty dense. You can definitely fit one in a QR code, they just start to become less reliable to scan (especially on cheap devices), and they go from looking nice to looking quite ugly. Technically most X.509 certs would have been within the limitations of QR codes (though I don’t think there is an upper bound to how large they can get), but I realized it just wasn’t fit for purpose and moved on to something else.
- matheusmoreira 7y ago
  Are you using 8 bit encoding? An alphanumeric mode QR code containing base 64 encoded data provides less capacity. In binary mode even a 4096 bit RSA secret key fits while ECC keys produce smaller codes. The qrencode tool has an 8 bit mode but not all decoders can handle binary data. For example, my phone shows me mangled results and I can't redirect them to a file. Like structured append, it doesn't seem to have much support. I've sent patches to ZBar improving this: https://github.com/mchehab/zbar/pull/64 https://github.com/mchehab/zbar/pull/64 Hopefully it will make QR codes more useful for storing keys and other small files.

BiteCode_dev 7y ago

7kb for a supermarket bill is plenty, and you can have several of them. Forms and legal documents should all have an immutable official url and uuid anyway to point to their legal and administrative context.

michaelt 7y ago
The largest QR code in the standard, "version 40" - can only store 3 kilobytes at the lowest level of error correction and 1.2 kilobytes at the highest level [1]. And that's a pretty huge QR code [2] My back-of-the-envelope calculations say you'd need 61 bits per line on a receipt just to encode UPC, quantity and price. So the largest QR code would only allow 19-50 lines. And that's without including data like the store name, special offers, means of payment and so on. Believe me, plenty of people buy more than 50 items in their supermarket christmas shop :) Standardised digital receipts would be neat but, QR codes encoding the data ain't the way to go about it. [1] https://www.qrcode.com/en/about/version.html https://www.qrcode.com/en/about/version.html [2] https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg
- smegger001 7y ago
  it could just contain a url linking to a page with to content.
- jlgaddis 7y ago
  Seems like the obvious thing would be to have the QR code contain a "receipt ID" (UUID?) in a URL. When the QR code is scanned, the browser opens to the URL, the remote side takes your "receipt ID", and presents you with a list of all the items you purchased. I can't imagine any decent-sized retailer isn't already maintaining records like this.
  - naniwaduni 7y ago
    See, one of the useful properties of a paper receipt is that, once you receive it, you can be fairly confident about the ~one way you're going to lose it

slim 7y ago

i think datamatrix is more suitable for x509

other_herbert 7y ago
Yes.. I had made a form that was scanned and all the metadata for the page was stored in datamatrix at the bottom.. With a laser printer and a good scanner you can reliably put a lot of data in there...

m-p-3 7y ago

I wish we could encode PGP public keys with them, but it's still too much data. That would be a neat way of exchanging a key.

prepend 7y ago
How big is your pgp public key? Mine is under 4K in ascii and can definitely fit in a QR code. If you use a crypto atm it will print out your wallet’s private and sometimes public keys as QR codes.
- AmericanChopper 7y ago
  4K is around the point where some devices will start to have issues scanning. Also, crypto wallets won’t usually give you the private key, instead they’ll give you the 12 word BIP39 seed phrase which will be around 70-80 bytes.
StavrosK 7y ago
You can definitely encode ed25519 keys to a QR code.
BiteCode_dev 7y ago
Gpg key fingerprints are very small though and can be used for that.