send_pubkey_test: no mutual signature algorithm (on newer sftp clients)

[ckhung]

Hi, I am running primitive ftpd 7.1 from f-droid on my phone. I am in the process of upgrading my computer OS from linux mint debian edition 5 to debian bookworm 12.5. I use ssh-add on both systems. Doing sftp from the old system (LMDE5) works fine, but doing it from the new system (Deb 12.5) receives "connection refused" even though the new system connects to my other servers quite well with the same ssh identity.

So I found this QA and tried scp -O ... from the new system, and it worked!

I also tried grml linux live cd's: grml32-small_20*.iso. For the older 2020-06 and 2021-07, it works. For the newer 2022-11, it fails. Comparing the log files generated by the -vvv option, the relevant differences are here:

# successful, on older clients
debug1: Offering public key: /root/.ssh/id_rsa RSA SHA256:... agent
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 60
debug1: Server accepts key: /root/.ssh/id_rsa RSA SHA256:... agent

vs:

# failed, on newer clients
debug1: Offering public key: /root/.ssh/id_rsa RSA SHA256:... agent
debug1: send_pubkey_test: no mutual signature algorithm

I have searched open and closed issues and I think they are not the same as this one, so here it goes. Maybe you can put some reminder about -O in the README file so that users know what to do before this issue is fixed.

Thank you so much for your work on primitive ftpd!

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edit: correction: should be "scp -O ..." not "sftp -O ..."

[wolpi]

Interessting to hear.
A hint in README has been added.