Linux Generate Private Key For Client Connection From Server
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If yes, does user authentication use the session keys generated on the client and on the server, or just use the public and private keys on the client and on the server? By the way, is there some reference about how the process goes and uses the public and private keys and session keys on the server and on the client? Aug 19, 2019 2. Confirm the connection – type yes and hit Enter. Once it locates the idrsa.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. Once the connection has been established, it adds the public key on the remote server.
May 05, 2019 Secure Shell (SSH) is a cryptographic network protocol used for a secure connection between a client and a server and supports various authentication mechanisms. The two most popular mechanisms are passwords based authentication and public key based authentication.
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. /steam-key-generator-no-survey-2017.html.
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.
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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
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 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.
Create the file
Edit the file to add the new SSH configuration
Example configuration
Add configuration settings appropriate for your host VM.
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.
This article shows how to configure a SSH connection for authentication by using the public-key method. To do this, a key pair is created at the client, the public part of the key is transferred to the server, and afterwards the server is set up for key authentication. The user can log on to the server without a login password, only the password is required to protect the private key.The operating systems used in this article are on the one hand a Ubuntu 12.10 at the client side and a Ubuntu 12.04 at the server side.This guide was also validated working with Ubuntu 16.04 as client and server.
- 1On the client
- 2On the server
- 3Notes for other distributions
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On the client
The first configuration steps take place at the client side.
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Home folder rights
By default, Ubuntu sets the user home directory permissions to 755. Nevertheless, for security reasons, check whether the permissions are set to 755 on your system and change them if necessary:
:~$ sudo chmod 755 /home/<USER>
Generate keypair
In the first step, a key pair with ssh-keygen is created at the client. If you use Ubuntu 18.04 on the server, the package openssh-server will be installed in the version 7.6.[1] Since this version, RSA bit lengths smaller than 1024 bits are no longer accepted.[2] In this example, a bit length of 4096 bits is selected for the RSA keys:
Please note: It is recommended to protect the key with a passphrase for security reasons. This means that the key is not available in plain text, but is AES-CBC encrypted:
If the private key is stolen by an attacker, he has to find out the password of the key in order to access the server with the key. If the key is available in plain text, an attacker can use this stolen key to directly access the server.
Transfer the public key to the server
To transfer the public key to the server, the first step is to use the SSH connection via password authentication yet. The ssh-copy-id tool copies the corresponding identity file to the server:
The above-mentioned procedure has created the following entry in the /home/tktest/.ssh/authorized_keyson the server:
Test the key authentication
Now that the public key is transferred to the server, the connection can be tested from the client. In this case, it is important that the server does not ask for the user password, but of course the passphrase of the protected key is required!
The following dialog box appears for GUI-based systems:
After entering the password that protected the key when it was created, you are authenticated on the system:
On the server
This paragraph shows some additional configuration steps on the server side to harden the public-key authentication.
sshd configuration
In Ubuntu, it is generally sufficient to carry out the above-mentioned procedure for public-key authentication. In some situations it makes sense to deactivate password authentication completely.
Please note: After changing the following setting, it is no longer possible to log in with a password via ssh: PasswordAuthentication no.
https://lifedisakaiser.weebly.com/blog/3devolution-download-torrent. From the client, the connection is tested again:
In the above example, the dialog for entering the key password has been aborted. Since the log-on via password was deactivated, it was not possible to log-on to the system.
Forbid password authentication for just one user
Another way in which password authentication is not completely deactivated is to disable password authentication for specific users. This allows a user who does not have sudo privileges to log on to the server, for example. To gain root privileges, at least one additional password must be found for a user with sudo privileges. Plus, there's a way to completely exclude users from ssh:
This example:
- Prohibits SSH access for the user
test - Deactivates password authentication for the user
tktest - Password authentication is retained for all other users
Notes for other distributions
For other Linux distributions, the required steps may differ slightly. We would be happy to supplement our experiences with other distributions, which you are welcome to share with us via the feedback function.
Red Hat
One reader told us that the procedure described Red Hat does not work 1:1 in Red Hat. In the home directory of the user, the write permission was set for the group. After a chmod 755 it worked to connect via ssh to the server without asking for a password.
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References
- ↑Package: openssh-server (1:7.6p1-4) (packages.ubuntu.com)
- ↑OpenSSH 7.6 Release Notes (openssh.com)