SSH keys are created using a key generation tool. The SSH command line tool suite includes a keygen tool. Most git hosting providers offer guides on how to create an SSH Key. Generate an SSH Key on Mac and Linux. Both OsX and Linux operating systems have comprehensive modern terminal applications that ship with the SSH suite installed. SSH keys are created using a key generation tool. The SSH command line tool suite includes a keygen tool. Most git hosting providers offer guides on how to create an SSH Key. Generate an SSH Key on Mac and Linux. Both OsX and Linux operating systems have comprehensive modern terminal applications that ship with the SSH suite installed. Sep 06, 2019 Keys can also be distributed using Ansible modules. The opensshkeypair module uses ssh-keygen to generate keys and the authorizedkey module adds and removes SSH authorized keys for particular user accounts. SSH key pairs are only one way to automate authentication without passwords.
Introduction
Secure Shell (SSH) is an encrypted protocol used by Linux users to connect to their remote servers.
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.
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.
Generate Ssh Login Key Linux Password
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 a Linux virtual machine on Azure that defaults to using SSH keys for authentication, eliminating the need for passwords to sign in. VMs created with the Azure portal, Azure CLI, Resource Manager templates, or other tools can include your SSH public key as part of the deployment, which sets up SSH key authentication for SSH connections.
This article provides detailed background and steps to create and manage an SSH RSA public-private key file pair for SSH client connections. If you want quick commands, see How to create an SSH public-private key pair for Linux VMs in Azure.
For additional ways to generate and use SSH keys on a Windows computer, see How to use SSH keys with Windows on Azure.
Overview of SSH and keys
SSH is an encrypted connection protocol that allows secure sign-ins over unsecured connections. SSH is the default connection protocol for Linux VMs hosted in Azure. Although SSH itself provides an encrypted connection, using passwords with SSH connections still leaves the VM vulnerable to brute-force attacks or guessing of passwords. A more secure and preferred method of connecting to a VM using SSH is by using a public-private key pair, also known as SSH keys.
The public key is placed on your Linux VM, or any other service that you wish to use with public-key cryptography.
The private key remains on your local system. Protect this private key. Do not share it.
When you use an SSH client to connect to your Linux VM (which has the public key), the remote VM tests the client to make sure it possesses the private key. If the client has the private key, it's granted access to the VM.
Depending on your organization's security policies, you can reuse a single public-private key pair to access multiple Azure VMs and services. You do not need a separate pair of keys for each VM or service you wish to access.
Your public key can be shared with anyone, but only you (or your local security infrastructure) should possess your private key.
Private key passphrase
The SSH private key should have a very secure passphrase to safeguard it. This passphrase is just to access the private SSH key file and is not the user account password. When you add a passphrase to your SSH key, it encrypts the private key using 128-bit AES, so that the private key is useless without the passphrase to decrypt it. If an attacker stole your private key and that key did not have a passphrase, they would be able to use that private key to sign in to any servers that have the corresponding public key. If a private key is protected by a passphrase, it cannot be used by that attacker, providing an additional layer of security for your infrastructure 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.
SSH keys use and benefits
When you create an Azure VM by specifying the public key, Azure copies the public key (in the .pub format) to the ~/.ssh/authorized_keys folder on the VM. SSH keys in ~/.ssh/authorized_keys are used to challenge the client to match the corresponding private key on an SSH connection. In an Azure Linux VM that uses SSH keys for authentication, Azure configures the SSHD server to not allow password sign-in, only SSH keys. Therefore, by creating an Azure Linux VM with SSH keys, you can help secure the VM deployment and save yourself the typical post-deployment configuration step of disabling passwords in the sshd_config file.
If you do not wish to use SSH keys, you can set up your Linux VM to use password authentication. If your VM is not exposed to the Internet, using passwords may be sufficient. However, you still need to manage your passwords for each Linux VM and maintain healthy password policies and practices, such as minimum password length and regular updates. Using SSH keys reduces the complexity of managing individual credentials across multiple VMs.
Generate keys with ssh-keygen
To create the keys, a preferred command is ssh-keygen, which is available with OpenSSH utilities in the Azure Cloud Shell, a macOS or Linux host, the Windows Subsystem for Linux, and other tools. ssh-keygen asks a series of questions and then writes a private key and a matching public key.
SSH keys are by default kept in the ~/.ssh directory. If you do not have a ~/.ssh directory, the ssh-keygen command creates it for you with the correct permissions.
Basic example
The following ssh-keygen command generates 2048-bit SSH RSA public and private key files by default in the ~/.ssh directory. If an SSH key pair exists in the current location, those files are overwritten.
Detailed example
The following example shows additional command options to create an SSH RSA key pair. If an SSH key pair exists in the current location, those files are overwritten.
Command explained
ssh-keygen = the program used to create the keys
-m PEM = format the key as PEM
-t rsa = type of key to create, in this case in the RSA format
-b 4096 = the number of bits in the key, in this case 4096
-C 'azureuser@myserver' = a comment appended to the end of the public key file to easily identify it. Normally an email address is used as the comment, but use whatever works best for your infrastructure.
-f ~/.ssh/mykeys/myprivatekey = the filename of the private key file, if you choose not to use the default name. A corresponding public key file appended with .pub is generated in the same directory. The directory must exist.
-N mypassphrase = an additional passphrase used to access the private key file.
Example of ssh-keygen
Saved key files
Generate Ssh Key Linux Redhat
Enter file in which to save the key (/home/azureuser/.ssh/id_rsa): ~/.ssh/id_rsa
The key pair name for this article. Having a key pair named id_rsa is the default; some tools might expect the id_rsa private key file name, so having one is a good idea. The directory ~/.ssh/ is the default location for SSH key pairs and the SSH config file. If not specified with a full path, ssh-keygen creates the keys in the current working directory, not the default ~/.ssh.
List of the ~/.ssh directory
Generate Ssh Key Linux
Key passphrase
Enter passphrase (empty for no passphrase):
It is strongly recommended to add a passphrase to your private key. Without a passphrase to protect the key file, anyone with the file can use it to sign in to any server that has the corresponding public key. Adding a passphrase offers more protection in case someone is able to gain access to your private key file, giving you time to change the keys.
Generate keys automatically during deployment
If you use the Azure CLI to create your VM, you can optionally generate SSH public and private key files by running the az vm create command with the --generate-ssh-keys option. The keys are stored in the ~/.ssh directory. Note that this command option does not overwrite keys if they already exist in that location.
Provide SSH public key when deploying a VM
To create a Linux VM that uses SSH keys for authentication, provide your SSH public key when creating the VM using the Azure portal, CLI, Resource Manager templates, or other methods. When using the portal, you enter the public key itself. If you use the Azure CLI to create your VM with an existing public key, specify the value or location of this public key by running the az vm create command with the --ssh-key-value option.
If you're not familiar with the format of an SSH public key, you can see your public key by running cat as follows, replacing ~/.ssh/id_rsa.pub with your own public key file location:
Output is similar to the following (here redacted):
If you copy and paste the contents of the public key file into the Azure portal or a Resource Manager template, make sure you don't copy any additional whitespace or introduce additional line breaks. For example, if you use macOS, you can pipe the public key file (by default, ~/.ssh/id_rsa.pub) to pbcopy to copy the contents (there are other Linux programs that do the same thing, such as xclip).
If you prefer to use a public key that is in a multiline format, you can generate an RFC4716 formatted key in a pem container from the public key you previously created.
To create a RFC4716 formatted key from an existing SSH public key:
SSH to your VM with an SSH client
With the public key deployed on your Azure VM, and the private key on your local system, SSH to your VM using the IP address or DNS name of your VM. Replace azureuser and myvm.westus.cloudapp.azure.com in the following command with the administrator user name and the fully qualified domain name (or IP address):
If you provided a passphrase when you created your key pair, enter the passphrase when prompted during the sign-in process. (The server is added to your ~/.ssh/known_hosts folder, and you won't be asked to connect again until 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.
Use ssh-agent to store your private key passphrase
To avoid typing your private key file passphrase with every SSH sign-in, you can use ssh-agent to cache your private key file passphrase. If you are using a Mac, the macOS Keychain securely stores the private key passphrase when you invoke ssh-agent.
Generate Ssh Key Linux Azure
Verify and use ssh-agent and ssh-add to inform the SSH system about the key files so that you do not need to use the passphrase interactively.
Now add the private key to ssh-agent using the command ssh-add.
The private key passphrase is now stored in ssh-agent.
Use ssh-copy-id to copy the key to an existing VM
If you have already created a VM, you can install the new SSH public key to your Linux VM with a command similar to the following:
Create and configure an SSH config file
You can create and configure an SSH config file (~/.ssh/config) to speed up log-ins and to optimize your SSH client behavior.
The following example shows a simple configuration that you can use to quickly sign in as a user to a specific VM using the default SSH private key.
Linux Ssh Keypair
Create the file
Edit the file to add the new SSH configuration
Example configuration
Add configuration settings appropriate for your host VM.
Generate Ssh Login Key Linux Server
You can add configurations for additional hosts to enable each to use its own dedicated key pair. See SSH config file for more advanced configuration options.
Now that you have an SSH key pair and a configured SSH config file, you are able to sign in to your Linux VM quickly and securely. When you run the following command, SSH locates and loads any settings from the Host myvm block in the SSH config file.
The first time you sign in to a server using an SSH key, the command prompts you for the passphrase for that key file.
Next steps
Next up is to create Azure Linux VMs using the new SSH public key. Azure VMs that are created with an SSH public key as the sign-in are better secured than VMs created with the default sign-in method, passwords.