Centos Generate Ssh Key Pair
Introduction
Secure Shell (SSH) is an encrypted protocol used by Linux users to connect to their remote servers.
Step One: Creation of the RSA Key Pair. The first step in the installation process is to create the key pair on the client machine, which would, more often than not, be your own system. Users need to use the following command: ssh-keygen -o -b 4096 -t rsa. The above command kicks off the SSH Key installation process for users. Use the ssh-keygen command to generate SSH public and private key files. By default, these files are created in the /.ssh directory. You can specify a different location, and an optional password (passphrase) to access the private key file. If an SSH key pair with the same name exists in the given location, those files are overwritten.
Generally, there are two ways for clients to access their servers – using password based authentication or public key based authentication.
Using SSH keys for authentication is highly recommended, as a safer alternative to passwords.
This tutorial will guide you through the steps on how to generate and set up SSH keys on CentOS 7. We also cover connecting to a remote server using the keys and disabling password authentication.
1. Check for Existing Keys
Prior to any installation, it is wise to check whether there are any existing keys on the client machines.
Centos Generate Ssh Key
Open the terminal and list all public keys stored with the following command:
The output informs you about any generated keys currently on the system. If there aren’t any, the message tells you it cannot access /.ssh/id_*.pub , as there is no such file or directory.
2. Verify SSH is Installed
To check if thw package is installed, run the command:
If you already have SSH, the output tells you which version it is running. Currently, the latest version is OpenSSH 8.0/8.0p1.
Note: Refer to our guide If you need to install and enable SSH on your CentOS system.
Steps to Creating SSH keys on CentOS
Step 1: Create SSH Key Pair
1. Start by logging into the source machine (local server) and creating a 2048-bit RSA key pair using the command:
If you want to tighten up security measures, you can create a 4096-bit key by adding the -b 4096 flag:
2. After entering the command, you should see the following prompt:
3. To save the file in the suggested directory, press Enter. Alternatively, you can specify another location.
Note: If you already have a key pair in the proposed location, it is advisable to pick another directory. Otherwise it will overwrite existing SSH keys.
4. Next, the prompt will continue with:
Although creating a passphrase isn’t mandatory, it is highly advisable.
5. Finally, the output will end by specifying the following information:
Now you need to add the public key to the remote CentOS server.
You can copy the public SSH key on the remote server using several different methods:
- using the ssh-copy-id script
- using Secure Copy (scp)
- manually copying the key
The fastest and easiest method is by utilizing ssh-copy-id. If the option is available, we recommend using it. Otherwise, try any of the other two noted.
1. Start by typing the following command, specifying the SSH user account, and the IP address of the remote host:
If it is the first time your local computer is accessing this specific remote server you will receive the following output:
2. Confirm the connection – type yes and hit Enter.
3. Once it locates the id_rsa.pub key created on the local machine, it will ask you to provide the password for the remote account. Type in the password and hit Enter.
4. Once the connection has been established, it adds the public key on the remote server. This is done by copying the ~/.ssh/id_rsa.pub file to the remote server’s ~/.ssh directory. You can locate it under the name authorized_keys.
5. Lastly, the output tells you the number of keys added, along with clear instructions on what to do next:
1. First, set up an SSH connection with the remote user:
2. Next, create the ~/.ssh directory as well as the authorized_keys file:
3. Use the chmod command to change the file permission:
chmod 700 makes the file executable, while chmod 600 allows the user to read and write the file.
4. Now, open a new terminal session, on the local computer.
5. Copy the content from id_rsa.pub (the SSH public key) to the previously created authorized_keys file on the remote CentOS server by typing the command:
With this, the public key has been safely stored on the remote account.
1. To manually add the public SSH key to the remote machine, you first need to open the content from the ~/.ssh/id_rsa.pub file:
2. As in the image below, the key starts with ssh-rsa and ends with the username of the local computer and hostname of the remote machine:
3. Copy the content of the file, as you will need later.
4. Then, in the terminal window, connect to the remote server on which you wish to copy the public key. Use the following command to establish the connection:
5. Create a ~/.ssh directory and authorized_keys file on the CentOS server with the following command:
6. Change their file permission by typing:
7. Next, open the authorized_keys file with an editor of your preference. For example, to open it with Nano, type:
8. Add the public key, previously copied in step 2 of this section, in a new line in (under the existing content).
9. Save the changes and close the file.
10. Finally, log into the server to verify that everything is set up correctly.
Once you have completed the previous steps (creating an RSA Key Pair and copying the Public Key to the CentOS server), you will be able to connect to the remote host without typing the password for the remote account.
All you need to do is type in the following command:
If you didn’t specify a passphrase while creating the SSH key pair, you will automatically log in the remote server.
Otherwise, type in the passphrase you supplied in the initial steps and press Enter.
Once the shell confirms the key match, it will open a new session for direct communication with the server.
Although you managed to access the CentOS server without having to provide a password, it still has a password-based authentication system running on the machine. This makes it a potential target for brute force attacks.
You should disable password authentication entirely by following the outlined steps.
Note: Consider performing the following steps through a non-root account with sudo privileges, as an additional safety layer.
1. Using the SSH keys, log into the remote CentOS server which has administrative privileges:
2. Next, open the SSH daemon configuration file using a text editor of your choice:
3. Look for the following line in the file:
4. Edit the configuration by changing the yes value to no. Thus, the directive should be as following:
5. Save the file and exit the text editor.
6. To enable the changes, restart the sshdservice using the command:
7. Verify the SSH connection to the server is still functioning correctly. Open a new terminal window and type in the command:
In this article, you learned how to generate SSH key pairs and set up an SSH key-based authentication. We also covered copying keys to your remote CentOS server, and disabling SSH password authentication.
Next, You Should Read:
-->With a secure shell (SSH) key pair, you can create virtual machines (VMs) in Azure that use SSH keys for authentication, eliminating the need for passwords to sign in. This article shows you how to quickly generate and use an SSH public-private key file pair for Linux VMs. You can complete these steps with the Azure Cloud Shell, a macOS or Linux host, the Windows Subsystem for Linux, and other tools that support OpenSSH.
Note
VMs created using SSH keys are by default configured with passwords disabled, which greatly increases the difficulty of brute-force guessing attacks.
For more background and examples, see Detailed steps to create SSH key pairs.
For additional ways to generate and use SSH keys on a Windows computer, see How to use SSH keys with Windows on Azure.
Supported SSH key formats
Azure currently supports SSH protocol 2 (SSH-2) RSA public-private key pairs with a minimum length of 2048 bits. Other key formats such as ED25519 and ECDSA are not supported.
Create an SSH key pair
Use the ssh-keygen command to generate SSH public and private key files. By default, these files are created in the ~/.ssh directory. You can specify a different location, and an optional password (passphrase) to access the private key file. If an SSH key pair with the same name exists in the given location, those files are overwritten.
The following command creates an SSH key pair using RSA encryption and a bit length of 4096:
If you use the Azure CLI to create your VM with the az vm create command, you can optionally generate SSH public and private key files using the --generate-ssh-keys option. The key files are stored in the ~/.ssh directory unless specified otherwise with the --ssh-dest-key-path option. The --generate-ssh-keys option will not overwrite existing key files, instead returning an error. In the following command, replace VMname and RGname with your own values:
Provide an SSH public key when deploying a VM
To create a Linux VM that uses SSH keys for authentication, specify your SSH public key when creating the VM using the Azure portal, Azure CLI, Azure Resource Manager templates, or other methods:
If you're not familiar with the format of an SSH public key, you can display your public key with the following cat command, replacing ~/.ssh/id_rsa.pub with the path and filename of your own public key file if needed:
A typical public key value looks like this example:
If you copy and paste the contents of the public key file to use in the Azure portal or a Resource Manager template, make sure you don't copy any trailing whitespace. To copy a public key in macOS, you can pipe the public key file to pbcopy. Similarly in Linux, you can pipe the public key file to programs such as xclip.
The public key that you place on your Linux VM in Azure is by default stored in ~/.ssh/id_rsa.pub, unless you specified a different location when you created the key pair. To use the Azure CLI 2.0 to create your VM with an existing public key, specify the value and optionally the location of this public key using the az vm create command with the --ssh-key-values option. In the following command, replace VMname, RGname, and keyFile with your own values:
If you want to use multiple SSH keys with your VM, you can enter them in a space-separated list, like this --ssh-key-values sshkey-desktop.pub sshkey-laptop.pub.
Centos Generate Ssh Key Pair Windows
SSH into your VM
With the public key deployed on your Azure VM, and the private key on your local system, SSH into your VM using the IP address or DNS name of your VM. In the following command, replace azureuser and myvm.westus.cloudapp.azure.com with the administrator user name and the fully qualified domain name (or IP address):
If you specified a passphrase when you created your key pair, enter that passphrase when prompted during the login process. The VM is added to your ~/.ssh/known_hosts file, and you won't be asked to connect again until either the public key on your Azure VM changes or the server name is removed from ~/.ssh/known_hosts.
If the VM is using the just-in-time access policy, you need to request access before you can connect to the VM. For more information about the just-in-time policy, see Manage virtual machine access using the just in time policy.
Next steps
Centos Generate Ssh Key Pair In Linux
For more information on working with SSH key pairs, see Detailed steps to create and manage SSH key pairs.
If you have difficulties with SSH connections to Azure VMs, see Troubleshoot SSH connections to an Azure Linux VM.