SSH not working over WLAN (ssh enabled, ping works, tcpping on port 22 works)

Question

I know this has been asked several times, but I went through a lot of trying to connect from my PC to my Raspberry Pi via SSH and I don't get it to work.

My Setup:

• Raspberry Pi 3 Model B+
• Working RetroPie 4.4 installation
• Windows-PC with Putty

What I want to do:

• Connect with Putty to my raspberry Pi over SSH
• Preferrably over wlan, but I tried both cabled and wlan

What I tried/did:

• Tried to connect with Putty (wlan) --> I got a connection refused error
• Enabled SSH with the raspi-config tool
• Tried to connect with Putty again -->
• 
• Tried to ping the wlan-ip: success
• Tried to open a telnet session on port 22: success
• Tried tcpping on port 22: success
• Despite that: still the same error.
• Connected PC over a simple switch to the pi.
• Tried all of the above with the eth0 ip with same result as wlan.

I think I can be fairly sure that the SSH server is listening (ps -ef says so, too) and a connection could be established. I do not think it is a problem of putty as i see tons of people using it with their raspberrys. I do not think it is a wlan related problem as I get the same results on the wired connection.

Could anyone point me in a direction where the error might be located?

Thank a lot.

Answer 1

So I checked the server logs and found the following error multiple times:

Aug 19 11:52:44 retropie sshd[9707]: error: key_load_public: invalid format
Aug 19 11:52:44 retropie sshd[9707]: error: Could not load host key: /etc/ssh/ssh_host_rsa_key

I deleted the keys and reconfigured them:

sudo rm /etc/ssh/ssh_host*
sudo dpkg-reconfigure openssh-server

After a restart, the connection worked like a charm.