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Jun 06, 2014 Generate SSH Key Pair on CentOS SSH (Secure Shell) and SFTP (Secure FTP) support a very strong security model that can be used instead of the normal username and password authentication scheme. Generate Your Keys. A host key is a cryptographic key used for authenticating computers in the SSH protocol.
With a secure shell (SSH) key pair, you can create a Linux virtual machine that uses SSH keys for authentication. This article shows you how to create and use an SSH RSA public-private key file pair for SSH client connections.
- Jan 22, 2021 Step 1: Generate SSH Public/Private Key Pair on CentOS/RHEL Desktop. On your CentOS/RHEL desktop (not your server), enter the following command in a terminal window. Ssh-keygen -t rsa -b 4096. Where:-t stands for type. The above command generates an RSA type keypair. RSA is the default type.-b stands for bits. By default, the key is 3072 bits long.
- Re: Generating new ssh keys Post by TrevorH » Thu Jan 28, 2016 5:06 pm I'm pretty sure that if you just remove the /etc/ssh/sshdhost. files then it will automatically regenerate them on the next start.
- Generate Public Key. This method involves generating an SSH key pair on the source machine and place it on the destination machine by login into it manually. First, login into the source machine and create an SSH key pair using the following command. raj@server $ ssh-keygen. Output: Generating public/private rsa key pair.
If you want quick commands, see How to create an SSH public-private key pair for Linux VMs in Azure.
To create SSH keys and use them to connect to a from a Windows computer, see How to use SSH keys with Windows on Azure. You can also use the Azure portal to create and manage SSH keys for creating VMs in the portal.
Overview of SSH and keys
SSH is an encrypted connection protocol that provides secure sign-ins over unsecured connections. SSH is the default connection protocol for Linux VMs hosted in Azure. Although SSH provides an encrypted connection, using passwords with SSH connections still leaves the VM vulnerable to brute-force attacks. We recommend connecting to a VM over SSH using a public-private key pair, also known as SSH keys.
The public key is placed on your Linux VM.
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 has the correct 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 have access to your private key.
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. 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.
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, and Windows 10. 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 4096-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
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
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.
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 add a new SSH public key to your Linux VM using ssh-copy-id.
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.
Create the file.
Edit the file to add the new SSH configuration
Add configuration settings appropriate for your host VM. In this example, the VM name is myvm and the account name is azureuser.
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.
Last updated on May 26th, 2021 at 11:10 am.
In this post you’ll setup SSH keys for your server. You will setup SSH Key authentication so that you can log in via your Private and public Key.
Watch the video below or read the post below if you want to setup SSH Key authentication on your server.
Feel free to follow along with any Linux distro.
The steps of what we’ll do :
- Generate SSH keys on our Local Linux / Mac computer
- Copy our public key onto the Server
- Test if we can log in via the SSH key pair
- Disable root login and password Authentication.
Before continuing with this post, ensure you create a new Sudo user on your Linux server.
If you are using Windows, watch this video which will show you how to generate and enable SSH key pair login into your Linux Server.
Take Note :
You can generate the keys using default options whereby, the name of the keys will be the default names ( id_rsa & id_rsa.pub ) and their location will be the default location (.ssh) . Use this if you only have one server to manage or if it is your first server. For the purpose of this post,We’ll call this , Default generation of keys .
You can also change settings for where to store and how to name the keys. This is better because you can create multiple ssh key pairs for different users or servers. For the purpose of this post we’ll call this , Custom generation of keys.
In this post I will show you how to handle both scenarios, starting with default generation of keys.
A. Default generation of keys
In this case we will not change the name or location of the SSH keys. Let’s see how to generate , setup and login with our keys.
#1 Create Public and Private SSH Key pair
This part is done on your local computer NOT on the server.
First we need to generate the public and private SSH key pair. The public Key will later get added onto the server and the private key will stay on your computer.
Ssh Generate Host Keys Centos
The following command creates it in the default directory, which shall be output for you once it is created.
If you do ssh-keygen -t the key will be genrated with default key settings.
-b specifies the bits to be generated, in this case 4096 bits
-C is just a comment for the key. Read more about SSH options here.
After entering the command above, you will be asked :
Enter file in which to save the key
You can press enter to use the defaults.
Please note that if you change the name of the key or location of storage, how you login in will be slightly different. Later on, I will show you how to change the location of the key and its name and how to use it to log in.
Next you will be asked to enter a passphrase. A passphrase is like a password for your key. To improve security, enter one. Ensure you enter a passphrase/password you will remember.
Confirm the passphrase, then press enter.
You Key is now created. The path of your key will be shown to you once it is created. You can copy it or not. When we change the path and name of our keys, copying this path will be important for us. As for now, since we used the defaults, we really don’t care.
The final screenshot after generating your ssh keys:
You have your private and public key. The next step is to add the public SSH key to your Linux Server.
#2 Copy keys to remote server
Next, let us copy the public key to the Server.
Continue working on your local computer. This part is still being done on your local Linux or Mac Computer.
The user you are adding the public SSH key for, should be the new sudo user you created.
Run the following to add your public key to your server.
For example if my ip is 127.0.0.1 and my username is newuser2020, I will add it as follows;
When asked for any login credentials, enter them, then press enter.
If you are on a Mac, you may need to install ssh-copy-id .
You can install ssh-copy-id using Homebrew:
If you’re lost on this, just google how to install ssh-copy-id on a Mac.
Important:
ssh-copy-id [email protected] will only work if you did not change the path or name of the SSH key pair generated above.
#3 Change Key & Directory permissions
On Linux ,SSH keys must have a permission of 600 or more. Very open permissions will make SSH to report an error and refuse to run till the security issue is rectified.
This step is done on your server.
Log into your server using the user for whom you added the SSH keys.
We will change the permissions for .ssh directory and the authorized_keys file using the following command:
Then change ownership to your new user’s Folder. Do this if you are adding ssh keys for another user who isn’t root. In the following command, change all instances of joe with the username you are adding the key for.
The authorized_keys is the file on your server which contains your public keys.
You have now added your public SSH on the Server, the next step is to ensure that you can login using your keys.
#4 Confirm you can Log into server via the Private key
Now that you have added the key for your sudo user, the next step is to log in using the private key. test it to ensure it works.
To test this, open a new terminal window, then ssh into your server as follows:
For example if my ip is 127.0.0.1 and my username is newuser2020, I will log in as follows;
Disallow Root Login and Password Authentication
Since you can now log in with your new sudo user using SSH keys, a good security practice is to disallow root login and password authentication on your server.this can be configured in the SSH daemon’s configuration file. Open it using nano.
Look for the PermitRootLogin line, uncomment it, if it is commented. and set the value to no.
Ssh Generate Host Keys Centos 10
Do the same for the PasswordAuthentication line, which should be uncommented already:
Save and close the file. (CTRL X to exit and then Y to confirm changes . And then enter)
To apply the new settings, reload SSH.
B. Custom generation of keys.
In this next part, you will see how to change the default Key location plus name. With this method, you will have to reference the path of your keys when you log in.
The steps are all the same as above, therefore I will not provide further explanations as I did above.
#1 Generate the keys
This part is done on your local Mac or Linux PC.
First , create folder where you will store the keys. You can create it inside of .ssh directory. This is a nice way to group authentication keys for different servers or users.
I will call mine vultvesta to indicate that it is for a Server on Vultr, intended for VestaCP. Do not use sudo to create this directory.
Once the directory is created, the next step is to create the keys in that directory.
From the above command, note that:
vultvesta – This is the name of the folder I created above. Replace it with the name of your folder.
firstserver_rsa – This is the filename I want for my public and private keys. Use a name of your choice.
Then Enter passphrase and confirm passphrase.
Once it is created, copy and save the path for your keys. The path will be displayed on the terminal window once the SSH keys have been generated.
The created keys will be file-named firstserver_rsa and firstserver_rsa.pub. They will be stored in a folder named vultvesta .
#2 Add Public Key to the server
If you have multiple keys in your local pc use -i to specify the location of the correct keys. If you created your keys in a different directory as above also use -i to identify the public key to add to your server.
:
For instance, based on my created Key pair above and a newuser2020 for my ip 127.0.0.1 :
If you are on a Mac, you may need to install ssh-copy-id .
You can install ssh-copy-id using Homebrew:
If you’re lost on this, just google how to install ssh-copy-id on a Mac.
#3 Change permissions
We will change the permissions for .ssh folder and the default authorized_keys file using the following command:
Then change ownership to your new user’s Folder. Do this if you are adding ssh keys for another user who isn’t root. In the following command, change all instances of joe with the username you are adding the key for.
#4 Log in via SSH key
To log in via SSH, this time round you have to add the path of your key:
eg
The -i option , enables you to choose an identity file to be used to log in.
Once you confirm you can log in successfully, disable Root Login and Password Authentication as is directed above.
Linux has SSH standards across distros :
- The SSH keys are kept here by default: ~/.ssh
~ is an alias for the current users home directory. e.g., /home/myuser - The public key has the .pub extension.
- known server fingerprints are written to known_hosts on your local computer & server.
This is used to detect “man in the middle” attacks. If the host’s fingerprint changes, SSH will report an error. - On any Linux server, authorized_keys is used to store public keys. You can add multiple public keys , each must be in its own line.
- SSH keys must have a permission of 600 or more. Open permissions will make SSH to report an error and refuse to run till the security issue is rectified.
How to generate and set up SSH keys for logging into your Linux Server. You can now log into your RHEL/ CentOS / Debian / Ubuntu using SSH keys.
Ssh Generate Host Keys Centos 5
If you experience any errors feel free to leave a comment. I will help you get it right.
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