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Old 10-06-2014, 10:01 AM   #1
JockVSJock
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SSH client-to-server cipher error when logging into Red Hat Enterprise


Hello.

I'm trying to use PuTTY v5.8 from a Windows 7 Desktop to log into an Red Hat Linux Enterprise Server and I'm getting the following error:

Code:
Couldn't agree a client-to-server cipher (available: aes128-ctr, aes192-ctr, aes256-ctr)
I believe that all of the Red Hat Linux systems are setup correctly, with the following.

/etc/hosts.allow has the IP addres of the computer that I'm using at access the server

/etc/ssh/ssh_config has the following entry: ciphers aes128-ctr, aes192-ctr and aes256-ctr

/etc/sysconfig/iptables has the following entry: -A INPUT -s (my ip address) -p tcp -m tcp --dport 22 -j ACCEPT

I think I have the Linux servers ok, and I am able to SSH into other Linux servers too, so I've tried to match the PuTTY settings so they match the ones that I can't get to Vs the ones that I can get to.

I am not sure what I'm missing or what I'm not doing.

It has been recommended to upgrade the PuTTY client, however I also wanted to get others input.

thanks
 
Old 10-07-2014, 06:50 PM   #2
ttk
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You need to add a "Ciphers" line to /etc/ssh/sshd_config (or modify the existing line) to include at least one cipher supported by PuTTY, and then either restart or SIGHUP the sshd process so that it re-reads its configuration.

Note that /etc/ssh/sshd_config is different from the /etc/ssh/ssh_config file, which is for ssh clients running on the host. The /etc/ssh/sshd_config file is for the ssh server running on the host (which is what your PuTTY ssh client is connecting to). The contents of /etc/ssh/ssh_config has no effect on connections to the server.

See also the "Ciphers" section of http://linux.die.net/man/5/sshd_config

Alternatively, if the latest version of PuTTY supports one of the ciphers the server is configured to use, then upgrading PuTTY would also work.

Last edited by ttk; 10-07-2014 at 06:51 PM.
 
Old 10-08-2014, 07:12 AM   #3
JockVSJock
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Forgot to mention, when checking /etc/sshd/sshd_config, the following entry is found:

Ciphers aes128-ctr,aes192-ctr,aes256-ctr


I am going to upgrade my PuTTY Client from v5.8 to v6.0 (its the version approved by out info sec deptartment) to see if that fixes the issue.

thanks
 
Old 10-22-2014, 08:55 PM   #4
JockVSJock
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Have updated the PuTTY client from v5.8 to v6 and that fixed the issue.

Thanks.
 
  


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