Dropbear difficulties due to outdated version?

[Konstantin Tokarev]

> Sometime during the interval after I set that up, key-pair authentication
> has stopped working again. So I've had to re-enable username/password
> authentication. I'm now trying to determine why it happened that the
> key-pair authentication stopped working and am hoping I can somehow
> re-enable it.

You can debug most of connection issue by using ssh -v. In this case most
likely culprit is that your key pair was generated using outdated algorithms
which are disabled in modern OpenSSH (most likely "ssh-rsa" which was default
for a long time). If this is actually the case, you can try to generate new key pair
with modern algorithms supported by both OpenSSH and your version of Dropbear
(I guess it should be ecdsa, as ed25519 would require newer Dropbear).

-- Regards,
Konstantin