An SSH key consists of a pair of files. One is the private key, which you should never give to anyone. No one will ever ask you for it and if so, simply ignore them - they are trying to steal it. The other is the public key. When you generate your keys, you will use ssh-keygen to store the keys in a safe location so you can authenticate with. Sep 26, 2019 To generate SSH keys in macOS, follow these steps: Enter the following command in the Terminal window. Press the ENTER key to accept the default location. Type in a passphrase. You can also hit the ENTER key to accept the default (no passphrase).
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Password authentication is the default method most SSH (Secure Shell) clients use to authenticate with remote servers, but it suffers from potential security vulnerabilities, like brute-force login attempts. An alternative to password authentication is public key authentication, in which you generate and store on your computer a pair of cryptographic keys and then configure your server to recognize and accept your keys. Using key-based authentication offers a range of benefits:
This guide will explain how the SSH key login scheme works, how to generate an SSH key, and how to use those keys with your Linode.
Note
If you’re unfamiliar with SSH connections, review the Getting Started with Linode guide.
How SSH Keys Work
SSH keys are generated in pairs and stored in plain-text files. The key pair (or keypair) consists of two parts:
When a site or service asks for your SSH key, they are referring to your SSH public key (
id_rsa.pub ). For instance, services like GitHub and Gitlab allow you to place your SSH public key on their servers to streamline the process of pushing code changes to remote repositories.
The authorized_keys File
In order for your Linode to recognize and accept your key pair, you will need to upload your public key to your server. More specifically, you will need to upload your public key to the home directory of the user you would like to log in as. If you would like to log in to more than one user on the server using your key pair, you will need to add your public key to each of those users.
Generate Ssh Key Aix
To set up SSH key authentication for one of your server’s users, add your public key to a new line inside the user’s
authorized_keys file. This file is stored inside a directory named .ssh/ under the user’s home folder. A user’s authorized_keys file can store more than one public key, and each public key is listed on its own line. If your file contains more than one public key, then the owner of each key listed will be able to log in as that user.
Granting Someone Else Access to your Server
To give someone else access to your server’s user, simply add their public key on a new line in your
authorized_keys file, just as you would add your own. To revoke access for that person, remove that same line and save the changes.
Challenge-Response
When logging in to a server using SSH, if there is a public key on file on that server, the server will create a challenge. This challenge will be crafted in such a way that only the holder of the private SSH key will be able to decipher it.
This challenge-response action happens without any user interaction. If the person attempting to log in has the corresponding private key, then they will be safely logged in. If not, the login will either fail or fall back to a password-based authentication scheme.
SSH Key Passphrases
You can optionally provide an additional level of security for your SSH keys by encrypting them with a passphrase at the time of creation. When you attempt to log in using an encrypted SSH key, you will be prompted to enter its passphrase. This is not to be confused with a password, as this passphrase only decrypts the key file locally and is not transferred over the Internet as a password might be.
If you’d like to set up your logins so that they require no user input, then creating a passphrase might not be desirable, but it is strongly recommended nevertheless.
Linux and macOSGenerate a Key Pair
Perform the steps in this section on your local machine.
Upload your Public Key
There are a few different ways to upload your public key to your Linode from Linux and macOS client systems: https://juicysupernal832.weebly.com/blog/aspnet-mvc-machine-key-generator.
Using ssh-copy-idssh-copy-id is a utility available on some operating systems that can copy a SSH public key to a remote server over SSH.
Using Secure Copy (scp)
Secure Copy ( Caution
scp ) is a tool that copies files from a local computer to a remote server over SSH:
These instructions will overwrite any existing contents of the
authorized_keys file on your server. If you have already set up other public keys on your server, use the ssh-copy-id command or enter your key manually.
Manually Copy an SSH Key
You can also manually add an SSH key to a server:
Connect to the Remote Server
Windows
The following instructions use the PuTTY software to connect over SSH, but other options are available on Windows too.
Generate a Key Pair with PuTTY
Manually Copy the SSH Key with PuTTY
Using WinSCP
Uploading a public key from Windows can also be done using WinSCP:
Caution
These instructions will overwrite any existing contents of the
authorized_keys file on your server. If you have already set up other public keys on your server, use the PuTTY instructions instead.
Connect to the Remote Server with PuTTY
Start PuTTY and Load your saved session. You’ll be prompted to enter your server user’s login name as before. However, this time you will be prompted for your private SSH key’s passphrase rather than the password for your server’s user. Enter the passphrase and press Enter.
Troubleshooting
If your SSH connections are not working as expected, or if you have locked yourself out of your system, review the Troubleshooting SSH guide for troubleshooting help.
Upload your SSH Key to the Cloud Manager
It is possible to provision each new Linode you create with an SSH public key automatically through the Cloud Manager.
Next Steps
After you set up your SSH keys and confirm they are working as expected, review the How to Secure Your Server guide for instructions on disabling password authentication for your server.
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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 .
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
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