Announcing paperbackup.py to backup keys as QR codes on paper

[Peter Lebbing]

On 23/02/17 13:36, Gerd v. Egidy wrote:
> So I think that this would move the bar for a possible user of paperbackup.py 
> higher than I want to.

Yes, it should be easy to use. In fact, I've sometimes heard the 
complaint that "paperkey is not easy to install and/or use". That's 
really too bad that those people feel that way.

> Ideally it is a tool or combination of tools already deployed widely, like sed 
> and sort I used in paperrestore. This would make the checksums still usable 
> even when the source to paperbackup.py isn't available anymore.

It took me some fiddling... but using CRC RevEng[1] I got a checksum in 
Python that is compatible to POSIX cksum.

The following Python:

>>> from posixcksum import PosixCkSum
>>> from base64 import b64encode
>>> crc, _ = PosixCkSum.sum_whole(bytearray(b'123456789'))
>>> b64encode(crc.to_bytes(4,byteorder='big'))[:4]
b'N3pg'

generates the same checksums as the following Bash code:

$ printf $(printf '%08x' $(echo -n 123456789 | cksum | cut -d' ' -f1) | sed 's/../\\x\0/g')|base64|cut -b-4
N3pg

This is done with the attached Python code. It is written for 
compactness rather than speed. Just re-implementing the crc function 
would probably be quicker.

HTH,

Peter.

[1] <http://reveng.sourceforge.net/>
-- 
I use the GNU Privacy Guard (GnuPG) in combination with Enigmail.
You can send me encrypted mail if you want some privacy.
My key is available at <http://digitalbrains.com/2012/openpgp-key-peter>
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