My SSH connections worked well, but from last week SSH from my laptop to my board refusing connection. I can make a SSH connection from the board to laptop, but not vice-versa. I tried that with my user and root user and had same issue.

My Laptop is an Ubuntu 12.10 and my board is a Debian 6.

Here is the verbose output of SSH:

danialbehzadi@danial-HP:~$ ssh -v  
OpenSSH_5.2p1, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /usr/local/etc/ssh_config
debug1: Connecting to [] port 22.
debug1: Connection established.  
debug1: identity file /home/danialbehzadi/.ssh/identity type -1  
debug1: identity file /home/danialbehzadi/.ssh/id_rsa type 1  
debug1: identity file /home/danialbehzadi/.ssh/id_dsa type -1  
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.0p1 Debian-4  
debug1: match: OpenSSH_6.0p1 Debian-4 pat OpenSSH*  
debug1: Enabling compatibility mode for protocol 2.0  
debug1: Local version string SSH-2.0-OpenSSH_5.2  
debug1: SSH2_MSG_KEXINIT sent  
debug1: SSH2_MSG_KEXINIT received  
debug1: kex: server->client aes128-ctr hmac-md5 none  
debug1: kex: client->server aes128-ctr hmac-md5 none  
no hostkey alg

I made new rsa and dsa keys on the board and it went OK:

~# ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key
~# ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key
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  • On a related note, When I tried to connect from dropbear ssh (common on android) to cygwin's sshd, I got "no matching algo hostkey". The server was set to accept key and password so it should've gone to password if the key fails. So I think this solution might not work for some.. According to this link it's to do with the encryption algorithm used linksysinfo.org/index.php?threads/tomato-ssh.29460 but no solution mentioned there. – barlop Sep 5 '14 at 10:57
  • 1
    We had the same problem with a ubuntu server 14.04. After trying to start a new instance of ssh server in debug mode, we found that private keys on the server did not have 0600 permission, once we fixed that and restarted the server, everything started working ok. – Awi Jul 10 '15 at 20:51

[root@server ~]# ls -la /etc/ssh/ssh_host_*

-rw-------. 1 root root      668 Jun 25 00:03 /etc/ssh/ssh_host_dsa_key
-rw-r--r--. 1 root root      609 Jun 25 00:03 /etc/ssh/ssh_host_dsa_key.pub
-rw-r-----. 1 root ssh_keys  227 Dec 14  2018 /etc/ssh/ssh_host_ecdsa_key
-rw-r--r--. 1 root root      162 Dec 14  2018 /etc/ssh/ssh_host_ecdsa_key.pub
-rw-r-----. 1 root ssh_keys  387 Dec 14  2018 /etc/ssh/ssh_host_ed25519_key
-rw-r--r--. 1 root root       82 Dec 14  2018 /etc/ssh/ssh_host_ed25519_key.pub
-rw-------. 1 root root      963 Apr 18  2011 /etc/ssh/ssh_host_key
-rw-r--r--. 1 root root      627 Apr 18  2011 /etc/ssh/ssh_host_key.pub
-rw-------. 1 root root     1679 Jun 25 00:02 /etc/ssh/ssh_host_rsa_key
-rw-r--r--. 1 root root      401 Jun 25 00:02 /etc/ssh/ssh_host_rsa_key.pub

make sure file ssh_host_* mode is 644 and 600 like this

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