ssh-keygen generates, manages and converts the authentication keys (private and public keys) used by SSH. You can generate both RSA and DSA keys. You can also generate Diffie-Hellman groups.
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1. Create RSA Keys
Halo 2 cd key. Aug 07, 2019 Create the ssh key pair using ssh-keygen command. Copy and install the public ssh key using ssh-copy-id command on a Linux or Unix server. Add yourself to sudo or wheel group admin account. Disable the password login for root account. Log into the computer you'll use to access the remote host, and then use command-line SSH to generate a key pair using the RSA algorithm. You will be prompted to supply a filename (for saving the key pair) and a password (for protecting your private key): Filename: To accept the default.
This is the default behaviour of ssh-keygen without any parameters. By default it creates RSA keypair, stores key under ~/.ssh directory. Note that the file name it created was id_rsa for private key and id_rsa.pub for public key.
2. Create DSA keys
To create DSA key, pass -t dsa as an argument.
Please note that it still stores the keys under ~/.ssh directory. But now the file name it created was id_dsa for private key and id_dsa.pub for public key.
3. Specify Key Filename and Location
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If you don’t want to store the key files under the default location use the -f option. Apart from storing it in a different directory, you can also specify your own name for the key files.
The following example will store the key files under /root directory. The name of the files will be my-key for private key, and my-key.pub for public key.
4. Specify Custom Comment to the Keys
By default, the keys generated will have “username@hostname” as comment. In all the above example, you can see “root@devdb” as the comment.
The following example will generate the RSA keys with the comment specified.
5. Convert SSH keys to Different Format
By default the keys generated by ssh-keygen will be used by the OpenSSH implementation. But, if you want to convert those keys to SSH comercial implementations (for example: SSH2), use the -e option as shown below.
You can use the following to specify the file and store the output to a different file.
6. Search Known Hosts File
You can also use ssh-keygen to search for keys in the ~/.ssh/known_hosts files. This is helpful when you have lot of entries in the known_hosts file.
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The following output indicates that it found the entry for “dev-db” in the known-hosts file at line#10.
7. Display the Public Key for given Private
The following example will display the public key for the default /root/.ssh/id_rsa private key.
You can also specify the priviate key using -f option. In this example, it will display the public key for ~/.ssh/id_dsa private key.
I 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?This page explains a public key and shows you how to set up SSH keys on a Linux or Unix-like server. I am assuming that you are using Linux or Unix-like server and client with the following software:
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- OpenSSH SSHD server
- OpenSSH ssh client and friends on Linux (Ubuntu, Debian, {Free,Open,Net}BSD, RHEL, CentOS, MacOS/OSX, AIX, HP-UX and co).
What is a public key authentication?
OpenSSH server supports various authentication schema. The two most popular are as follows:
- Passwords based authentication
- Public key based authentication. It is an alternative security method to using passwords. This method is recommended on a VPS, cloud, dedicated or even home based server.
How to set up SSH keys
Steps to setup secure ssh keys:
- Create the ssh key pair using ssh-keygen command.
- Copy and install the public ssh key using ssh-copy-id command on a Linux or Unix server.
- Add yourself to sudo or wheel group admin account.
- Disable the password login for root account.
- Test your password less ssh keys login using ssh user@server-name command.
Let us see all steps in details.
How do I set up public key authentication?
You must generate both a public and a private key pair. For example:
Where,
Where,
- server1.cyberciti.biz – You store your public key on the remote hosts and you have an accounts on this Linux/Unix based server.
- client1.cyberciti.biz – Your private key stays on the desktop/laptop/ computer (or local server) you use to connect to server1.cyberciti.biz server. Do not share or give your private file to anyone.
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:
1: Create the key pair
On the computer (such as client1.cyberciti.biz), generate a key pair for the protocol.
Sample outputs:
Many Git servers authenticate using SSH public keys. In order to provide a public key, each user in your system must generate one if they don’t already have one. This process is similar across all operating systems. First, you should check to make sure you don’t already have a key. If you're unsure whether you already have an SSH key, check for existing keys. If you don't want to reenter your passphrase every time you use your SSH key, you can add your key to the SSH agent, which manages your SSH keys and remembers your passphrase. Generating a new SSH key. Open Terminal Terminal Git Bash. Git bash ssh key generate 2017.
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:
- $HOME/.ssh/id_rsa– contains your private key.
- $HOME/.ssh/id_rsa.pub – contain your public key.
Optional syntax for advance users
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The following syntax specifies the 4096 of bits in the RSA key to creation (default 2048):
Where,
$ ssh-keygen -t rsa -b 4096 -f ~/.ssh/vps-cloud.web-server.key -C 'My web-server key'
Where,
- -t rsa : Specifies the type of key to create. The possible values are “rsa1” for protocol version 1 and “dsa”, “ecdsa”, “ed25519”, or “rsa” for protocol version 2.
- -b 4096 : Specifies the number of bits in the key to create
- -f ~/.ssh/vps-cloud.web-server.key : Specifies the filename of the key file.
- -C 'My web-server key' : Set a new comment.
2: Install the public key in remote server
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., [email protected]). 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:
A note about appending the public key in remote server
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:
3: Test it (type command on client1.cyberciti.biz)
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.
What are ssh-agent and ssh-add, and how do I use them?
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 [email protected] and you will not be prompted for a password:
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One can list public key parameters of all identities with the -L option:
Deleting all private keys from the ssh-agent can be done with the -D option as follows:
When you log out kill the ssh agent, run:
You can also add something like the below to your shell startup to kill ssh-agent at logout:
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
4: Disable the password based login on a server
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:
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Save and close the file. I am going to add a user named vivek to sudoers on Ubuntu Linux:
Finally, reload/restart the sshd server, type command as per your Linux/Unix version:
# adduser vivek
Finally, reload/restart the sshd server, type command as per your Linux/Unix version:
5: How to add or replace a passphrase for an existing private key?
To to change your passphrase type the following command:
ssh-keygen -p
6: How do I backup an existing private/public key?
Just copy files to your backup server or external USB pen/hard drive:
How do I protect my ssh keys?
- Always use a strong passphrase.
- Do not share your private keys anywhere online or store in insecure cloud storage.
- Restrict privileges of the account.
How do I create and setup an OpenSSH config file to create shortcuts for servers I frequently access?
See how to create and use an OpenSSH ssh_config file for more info.
Conclusion
This page explained how to set up ssh keys for authentication purposes. For more info see the following resources:
- Man pages – ssh-keygen(1)
- OpenSSH project homepage here.
And, there you have it, ssh set up with public key based authentication for Linux or Unix-like systems.
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