Nov 10, 2011 How to Generate A Public/Private SSH Key Linux By Damien – Posted on Nov 10, 2011 Nov 18, 2011 in Linux If you are using SSH frequently to connect to a remote host, one of the way to secure the connection is to use a public/private SSH key so no password is transmitted over the network and it can prevent against brute force attack.
recently read that SSH keys provide a secure way of logging into a Linux and Unix-based server. How do I set up SSH keys on a Linux or Unix based systems? In SSH for Linux/Unix, how do I set up public key authentication?OpenSSH server supports various authentication schema. The two most popular are as follows:
Steps to setup secure ssh keys:
Let us see all steps in details.
You must generate both a public and a private key pair. For example:
Where,
In public key based method you can log into remote hosts and server, and transfer files to them, without using your account passwords. Feel free to replace server1.cyberciti.biz and client1.cyberciti.biz names with your actual setup. Enough talk, let’s set up public key authentication. Open the Terminal and type following commands if .ssh directory does not exists:
On the computer (such as client1.cyberciti.biz), generate a key pair for the protocol.
Sample outputs:
You need to set the Key Pair location and name. I recommend you use the default location if you do not yet have another key there, for example: $HOME/.ssh/id_rsa. You will be prompted to supply a passphrase (password) for your private key. I suggest that you setup a passphrase when prompted. You should see two new files in $HOME/.ssh/ directory:
The following syntax specifies the 4096 of bits in the RSA key to creation (default 2048):$ ssh-keygen -t rsa -b 4096 -f ~/.ssh/vps-cloud.web-server.key -C 'My web-server key'
Where,
Product key word 2010 generator. Use scp or ssh-copy-id command to copy your public key file (e.g., $HOME/.ssh/id_rsa.pub) to your account on the remote server/host (e.g., nixcraft@server1.cyberciti.biz). To do so, enter the following command on your client1.cyberciti.biz:
OR just copy the public key in remote server as authorized_keys in ~/.ssh/ directory:
On some system ssh-copy-id command may not be installed, so use the following commands (when prompted provide the password for remote user account called vivek) to install and append the public key:
The syntax is as follows for the ssh command:
Or copy a text file called foo.txt:
You will be prompted for a passphrase. To get rid of passphrase whenever you log in the remote host, try ssh-agent and ssh-add commands.
To get rid of a passphrase for the current session, add a passphrase to ssh-agent and you will not be prompted for it when using ssh or scp/sftp/rsync to connect to hosts with your public key. The syntax is as follows:
Type the ssh-add command to prompt the user for a private key passphrase and adds it to the list maintained by ssh-agent command:
Enter your private key passphrase. Now try again to log into user@server1.cyberciti.biz and you will not be prompted for a password:
One can list public key parameters of all identities with the -L option:ssh-add -L
Deleting all private keys from the ssh-agent can be done with the -D option as follows:ssh-add -D
When you log out kill the ssh agent, run:kill $SSH_AGENT_PID
You can also add something like the below to your shell startup to kill ssh-agent at logout:trap 'kill $SSH_AGENT_PID' 0
Login to your server, type:
Edit /etc/ssh/sshd_config on server1.cyberciti.biz using a text editor such as nano or vim:
Warning: Make sure you add yourself to sudoers files. Otherwise you will not able to login as root later on. See “How To Add, Delete, and Grant Sudo Privileges to Users on a FreeBSD Server” for more info.
$ sudo vim /etc/ssh/sshd_config
OR directly jump to PermitRootLogin line using a vim text editor:$ sudo vim +/PermitRootLogin /etc/ssh/sshd_config
Find PermitRootLogin and set it as follows:
Save and close the file. I am going to add a user named vivek to sudoers on Ubuntu Linux:# adduser vivek
Finally, reload/restart the sshd server, type command as per your Linux/Unix version:
To to change your passphrase type the following command:ssh-keygen -p
Just copy files to your backup server or external USB pen/hard drive:
See how to create and use an OpenSSH ssh_config file for more info.
This page explained how to set up ssh keys for authentication purposes. For more info see the following resources:
And, there you have it, ssh set up with public key based authentication for Linux or Unix-like systems.
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