Oct 14, 2019  Generating ed25519 SSH Key. I'm hoping to reinstall my MacBook Pro 15' 2017 with a fresh macOS Catalina sometime soon, and part of preparations is testing my install methods (hello, brew!) and configuration files migration. Today I decided to setup a new SSH keypair. What is ed25519? Ed25519 is a relatively new cryptography solution implementing Edwards-curve Digital Signature. Jul 29, 2019  Step 1- Generate the SSH Key Pair. On your client system – the one you’re using to connect to the server – you need to create a pair of key codes. To generate a pair of SSH key codes, enter the commands: This will create a hidden directory to store your. If you did not create more than one ssh key, you do not have to worry about specifying the identity, ssh-copy-id will just pick it automatically. In case you do not have an identity, you can generate one with the tool ssh-keygen. In order to generate a SSH key on Debian, you are going to need the ssh-keygen tool. By default, ssh-keygen is already installed on Debian 10. To create a SSH key pair, use the following command. $ ssh-keygen -t rsa -b 4096 -C 'email protected' This ssh-keygen will take care of creating your key.

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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.

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Ssh-keygen -t ecdsa -b 521 -C 'ECDSA 521 bit Keys' Generate an ed25519 SSH keypair- this is a new algorithm added in OpenSSH. Ssh-keygen -t ed25519 Extracting the public key from an RSA keypair. Openssl rsa -pubout -in privatekey.pem -out publickey.pem Extracting the public key from an DSA keypair. Openssl dsa -pubout -in privatekey.pem -out.

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

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.)

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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.

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Create the file

Edit the file to add the new SSH configuration

Example configuration

/intellij-idea-14-ultimate-keygen-license-key-generator-with-gui.html. Add configuration settings appropriate for your host VM.

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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.

You can login to a remote Linux server without entering password in 3 simple steps using ssky-keygen and ssh-copy-id as explained in this article.

ssh-keygen creates the public and private keys. ssh-copy-id copies the local-host’s public key to the remote-host’s authorized_keys file. ssh-copy-id also assigns proper permission to the remote-host’s home, ~/.ssh, and ~/.ssh/authorized_keys.

This article also explains 3 minor annoyances of using ssh-copy-id and how to use ssh-copy-id along with ssh-agent.

Step 1: Create public and private keys using ssh-key-gen on local-host

Step 2: Copy the public key to remote-host using ssh-copy-id

Note: ssh-copy-id appends the keys to the remote-host’s .ssh/authorized_key.

Step 3: Login to remote-host without entering the password

The above 3 simple steps should get the job done in most cases.

We also discussed earlier in detail about performing SSH and SCP from openSSH to openSSH without entering password.

If you are using SSH2, we discussed earlier about performing SSH and SCP without password from SSH2 to SSH2 , from OpenSSH to SSH2 and from SSH2 to OpenSSH.

Using ssh-copy-id along with the ssh-add/ssh-agent

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When no value is passed for the option -i and If ~/.ssh/identity.pub is not available, ssh-copy-id will display the following error message.

If you have loaded keys to the ssh-agent using the ssh-add, then ssh-copy-id will get the keys from the ssh-agent to copy to the remote-host. i.e, it copies the keys provided by ssh-add -L command to the remote-host, when you don’t pass option -i to the ssh-copy-id.

Three Minor Annoyances of ssh-copy-id

Following are few minor annoyances of the ssh-copy-id.

1. Default public key: ssh-copy-id uses ~/.ssh/identity.pub as the default public key file (i.e when no value is passed to option -i). Instead, I wish it uses id_dsa.pub, or id_rsa.pub, or identity.pub as default keys. i.e If any one of them exist, it should copy that to the remote-host. If two or three of them exist, it should copy identity.pub as default.
2. The agent has no identities: When the ssh-agent is running and the ssh-add -L returns “The agent has no identities” (i.e no keys are added to the ssh-agent), the ssh-copy-id will still copy the message “The agent has no identities” to the remote-host’s authorized_keys entry.
3. Duplicate entry in authorized_keys: I wish ssh-copy-id validates duplicate entry on the remote-host’s authorized_keys. If you execute ssh-copy-id multiple times on the local-host, it will keep appending the same key on the remote-host’s authorized_keys file without checking for duplicates. Even with duplicate entries everything works as expected. But, I would like to have my authorized_keys file clutter free.

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