Private key authentication fails after update [F-Droid]

Bug description

After upgrading from 1.9.6-oss to 1.9.8-oss on Android 11, I could no longer connect to the ssh server running on localhost. It would report some issue authenticating with my private key and instead prompt for ssh password auth (which I don’t have setup). When going into the key management menu of connectbot and tapping on the sole key that I have, it would report Wrong Password (so this is for the key, not for ssh auth). I don’t recall setting a password and I definitely never needed to enter a password to use this private key.

Server information

• OS: using the app Linux Deploy, it’s a mostly Debian 11 system
• SSH software: openssh-server 1:8.4p1-5 armhf from the repositories
• Pubkeys used: ed25519

Workaround

I could resolve the problem by downgrading, using termux:

$ wget https://f-droid.org/repo/org.connectbot_10906000.apk
$ cmd package install -d org.connectbot_10906000.apk

Where the -d flag allows downgrading.

[kruton]

It might be an encoding problem. I switched libraries for Ed25519 between 1.9.6 and 1.9.8, so the reading of old keys might be affected. I’ll check this out.

[normanr]

ahh, the old connection seems to be sending a server_host_key_algorithms of ssh-rsa in the Client Key Exchange Init step. sshd logs an error of Unable to negotiate with $remote: no matching host key type found. Their offer: ssh-rsa [preauth]. The newer connection offers only ssh-ed25519 at the same point.

ahh, this is already reported at the bottom of #747, sorry for the noise