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.

1. Create RSA Keys

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.

The simplest way I found to do what you want is this (example using default filename) cat /dev/zero ssh-keygen -q -N '. If the /.ssh/idrsa file already exists, the command will exit without modifying anything. If not, you get a brand new key, in that filename. If you interact regularly with SSH commands and remote hosts, you may find that using a key pair instead of passwords can be convenient. Instead of the remote system prompting for a password with each connection, authentication can be automatically negotiated using a public and private key pair.

3. Specify Key Filename and Location

I would like to make an automated script that calls ssh-keygen and creates some pub/private keypairs that I will use later on. In principle everything works fine with. Ssh-keygen -b 2048 -t rsa -f /tmp/sshkey -q.except that it asks me for the passphrase that would encrypt the keys. This make -at present- the automation difficult. SSH, the secure shell, is often used to access remote Linux systems. But its authentication mechanism, where a private local key is paired with a public remote key, is used to secure all kinds of online services, from GitHub and Launchpad to Linux running on Microsoft’s Azure cloud. Ssh-keygen is a standard component of the Secure Shell (SSH) protocol suite found on Unix, Unix-like and Microsoft Windows computer systems used to establish secure shell sessions between remote computers over insecure networks, through the use of various cryptographic techniques.

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.

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.

Establishing an SSH (Secure Shell) connection is essential to log in and effectively manage a remote server. Encrypted keys are a set of access credentials used to establish a secure connection.

This guide will show you how to generate SSH keys on Ubuntu 18.04. We will also cover setting up SSH key-based authentication to connect to a remote server without requiring a password.

• A server running Ubuntu 18.04, SSH enabled on Ubuntu
• A user account with sudo privileges
• Access to a terminal window/command line (Ctrl-Alt-T)

On your client system – the one you’re using to connect to the server – you need to create a pair of key codes.

To generate a pair of SSH key codes, enter the commands:

This will create a hidden directory to store your SSH keys, and modify the permissions for that directory. The ssh-keygen command creates a 2048-bit RSA key pair.

For extra security, use RSA4096:

If you’ve already generated a key pair, this will prompt to overwrite them, and those old keys will not work anymore.

The system will ask you to create a passphrase as an added layer of security. Input a memorable passphrase, and press Enter.

This process creates two keys. One is a public key, which you can hand out to anyone – in this case, you’ll save it to the server. The other one is a private key, which you will need to keep secure. The secure private key ensures that you are the only person who can encrypt the data that is decrypted by the public key.

First, get the IP address of the Ubuntu server you want to connect to.

In a terminal window, enter:

The system’s IP address is listed in the second entry:

On the client system, use the ssh-copy-id command to copy the identity information to the Ubuntu server:

Replace server_IP with the actual IP address of your server.

If this is the first time you’re connecting to the server, you may see a message that the authenticity of the host cannot be established:

Type yes and press Enter.

The system will check your client system for the id_rsa.pub key that was previously generated. Then it will prompt you to enter the password for the server user account. Type it in (the system won’t display the password), and press Enter.

The system will copy the contents of the ~/.ssh/id_rsa.pub from the client system into the ~/.ssh/authorized_keys directory of the server system.

The system should display:

If your system does not have the ssh-copy-id command, you can copy the key manually over the SSH.

Use the following command:

To log in to a remote server, input the command:

The system should not ask for a password as it is negotiating a secure connection using the SSH keys. If you used a security passphrase, you would be prompted to enter it. After you do so, you are logged in.

If this is the first time you’ve logged into the server, you may see a message similar to the one in part two. It will ask if you are sure you want to connect – type yes and press Enter.

Ssh Keygen Command Options

This step creates an added layer of security. If you’re the only person logging into the server, you can disable the password. The server will only accept a login with your private key to match the stored public key.

Edit the sshd_config file:

Search the file and find the PasswordAuthentication option.

Edit the file and change the value to no:

Save the file and exit, then restart the SSH service:

Verify that SSH is still working before ending the session:

If everything works, you can close out and resume work normally.

By following the instructions in this tutorial, you have setup SSH-key-based authentication on an Ubuntu 18.04 server.

The connection is now highly secure as it uses a set of unique, encrypted SSH keys.

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