Non-commercial version of SSH Secure Shell (can be obtained here) from SSH Communications Security is a decent ssh client that I have used for many years in my experiments and academic works. It lacks PKI and PKCS functionality, but still safe for experiments! However; when it comes to public key authentication, it needs some tweaks to work. Here are the steps required to enable key authentication over a Linux host; given that Linux host settings allow public/private key authentication:

1. Connect to the host using SSH Secure Shell (by password)
2. In Secure Shell client, go to: Edit -> Settings -> User Authentication -> Keys and click on ‘Generate New’
   
3. When generation is done, it will ask you to upload the public key to the host. Let it upload to ‘.ssh ‘ as destination folder.
   
4. It assumes that the host has the appropriate SSH server for this client (the company has SSH server too) but since standard Linux servers use OpenSSH as SSH server, uploading the public key to the host is not enough and needs some modifications that follows.
5. In Linux host, you will see that a public key (KeyAuthTest.pub in this case) is uploaded in ‘.ssh’ directory. For this to work, there are 2 ways:
   • Edit ‘KeyAuthTest.pub’ manually! and give it the right format. Remove these lines (or something like this) in the beginning:
     —- BEGIN SSH2 PUBLIC KEY —-
     Comment: “[3072-bit rsa, yyyy@xxxx, Thu Oct 04 2012 21:33:49]”
     And this at the end:
     —- END SSH2 PUBLIC KEY —-
     Also, you need to remove all the carriage returns (CR) in this file. Then add ‘ssh-rsa’ in the beginning of the file. The file would be something like:
     ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC+…
     Finally, in shell append this file to the ‘authorized_keys’ file :
     cat ~/.ssh/KeyAuthTest.pub >> ~/.ssh/authorized_keys
   • Second approach: convert the key to proper OpenSSH format automatically and append it to the file:
     ssh-keygen -i -f ~/.ssh/KeyAuthTest.pub  >>  ~/.ssh/authorized_keys

Now, you will be able to connect to the host, using this public key.