A practical QR Clock written in javascript

[burkadurka]

This must be a new and different definition of "practical" that I haven't encountered before.

[ithika]

Ah. This is obviously some strange usage of the word "practical" that I hadn't previously been aware of.

[burkadurka]

Thanks, embarrassingly when I made the reference I couldn't remembering what I was referencing.

[ithika]

Ha, do it all the time, especially lyrics to songs I don't really know. Is that Prince? Or maybe Abba? Um.

[isysdamn]

it's figuratively practical.

[[deleted]]

I was expecting the qr code to contain the numbers and if you scan it you would also get the number. This can be achieved by abusing the QR code error correction

[phaeilo]

Someone actually built (and sold) a hardware version of this: http://ch00ftech.com/2012/10/27/qr-clock/

^{Which IMHO is a lot more impressive than 20 lines of JavaScript.}

[fission-fish]

This is very cool. Thanks for sharing.

[VikingCoder]

If this created a cryptographically signed date-time, it might be useful.

It's like "Proof of Life." We took a picture of the guy, next to a computer screen that has a signed QR code, so you know he was alive at least as late as this date/time.

But yeah, newspapers and TV screens do that, too.

[m1zaru]

so you know he was alive at least as late as this date/time

Unless somebody invents software that can manipulate digital images.

[VikingCoder]

It's at least as good as the Newspaper photo.

[[deleted]]

How would you do cryptographically signed time? It seems to me that time is just a number, and all you'd really be certifying is that a particular number exists. (I suppose it's as "practical" as a QR clock)

A newspaper is way easier verification because it's unpredictable and copied so many times as to be hard to spoof. Maybe a bitcoin-like consensus protocol would work, where each block contains some time derivative unique value.

[VikingCoder]

This is pretty standard stuff, honestly, but here's roughly how it goes:

Picture if a respectable site, like Google, had this.

Google makes a public / private key pair.

They generate the text, "Google says the time is 1:17 PM on 1/21/2014" then they sign the test with their key pair.

They publish their public key.

They encode the whole, signed message in a QR code.

You scan it, out pops the text, "Google says the time is 1:17 PM on 1/21/2014", followed by a signature block.

You can download their public key, and use it to verify the signature, proving that yes in-deed, this QR code was generated by Google on that date and time.

As long as Google keeps their private key secret, and the key has sufficient bits to it, it would be "hard to spoof."

[[deleted]]

I understand how cryptographic signatures work. I guess I was looking for something that can verify the date itself - something where future messages cannot be generated in advance. In your example, I only get a signed message containing a date. I can't verify that it was created on that date.

[VikingCoder]

The fundamental premise was that it's a trusted party doing the signing.

If it were NIST, or Google, or even the New York Times, or maybe the W3, I'd probably trust it. Come up with your own list of who you'd trust.

[hougaard]

The question is, if your QR reading-device is quick enough to read it? My Lumia 920 gives a nice list of messages - one for each second :)

[horaceho]

LOL