Generate Syncthing Device ID from the certificate

spectras · September 23, 2016, 4:34pm

I did not find an easy way to do it, so I wrote a short python script from the description of the device ID in the documentation.

I figured it could be useful, so I’m sharing it here:

gist.github.com

https://gist.github.com/spectras/b3a6f0093ddb1635b39279e9a539ca21

syncthing_id.py

#!/usr/bin/env python
import base64
import hashlib
import subprocess
import sys

B32ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'

def luhn_checksum(data, alphabet=B32ALPHABET):
    n = len(alphabet)

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I use it for generating config.xml from a directory of certificates in my ansible scripts. I tested it with a few device ids, but I’d be even more confident if someone ran it on a few more.

calmh · September 23, 2016, 8:17pm

It looks correct to me, just by eyeballing it. If it does the right thing for one certificate / device ID it probably does so for all of them.

rumpelsepp · September 24, 2016, 1:45am

github.com

wiederma/st-ddns/blob/master/st-ddns.py#L49-L84


def _luhn_mod_sum(s):
# https://en.wikipedia.org/wiki/Luhn_mod_N_algorithm
a = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'
n = len(a)
factor = 1
k = 0
for i in s:
    addend = factor * a.index(i)
    factor = 1 if factor == 2 else 2
    addend = (addend // n) + (addend % n)
    k += addend
remainder = k % n
check_codepoint = (n - remainder) % n
return a[check_codepoint]




def _chunk_str(s, chunk_size):
return [s[i:i+chunk_size] for i in range(0, len(s), chunk_size)]

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This works for me.

calmh · September 24, 2016, 6:13am

What does that do, st-ddns?

rumpelsepp · September 24, 2016, 2:33pm

Don’t mind the silly name; it just announces a given cert and/or queries a given device id.