Basic QR scan functionality

[hryamzik]

Added basic QR scan functionality. Works in the same way as clipboard pasting: only RSA keys are supported. Could help with #244 but also affected with it - invalid string leads to an infinite loop.

Didn't have a chance to test with pass-phrases.

QR code could be generated with

brew install qrencode
cat id_rsa|qrencode -t png -o rsa.png && open rsa.png

or if your screen is large enough

cat id_rsa|qrencode -t ANSI256

ANSI256 works fine for ed25519 on reasonably-sized screens but it's not supported yet.

[hryamzik]

@carloscabanero I could also fix infinite loop reported in #244 and add other key formats support, but starting this work from current master will make new PR conflict with this one.

[carloscabanero]

Thanks a lot @hryamzik!!! Will definitely push to the next version. If you can add other key formats support, hit me up on cc (at) blink.sh and we can arrange something. We are currently evaluating to move to either PuTTy or libssh too, specially for other keys support and more features.

[hryamzik]

Is there anything preventing merge? Did I select wrong branch?

[hryamzik]

Looks like ed25519 isn't supported by libssh2 yet, that's bad news.

P.S.: OK, that's already discussed in #60.

[goerz]

It would be great if Blink could display its private keys as a QR code as well. I do like to use just one key for Blink on all of my different iOS devices. This way, I could generate a key on the iPad, display it as a QR code, and then simply import it to the iPhone by pointing the camera to the iPad screen. That seems more secure than having to email the key to myself, or anything like that.

[hryamzik]

I think private keys should be synced between devices with keychain, not QR codes.

[loot-king]

Update files

[hryamzik]

I don't have time to update this, feel free to push more changes here or to create a new PR.

[carloscabanero]

We did not do a good job at merging this and it has I think there are better ways at moving keys around now. Closing here.