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SSH authentication using private key stored on YubiKeys

1. Jan 23, 2017 You should have keys in your gpg agent via the YubiKey and in your SSH agent via the gpg agent. Testing SSH access is straight forward. We’ll capture SSH public key on the YubiKey and add it to.
2. The macOS Login Tool allows for secure two-factor authentication on Macs using the HMAC-SHA1 challenge-response feature of the YubiKey. Note: Enabling full disk encryption (FDE) with FileVault is highly recommended when using the macOS Login Tool. If you do not enable FDE, it is possible to reboot the Mac into recovery mode and disable the 2FA.

Mar 16, 2015  2018-12-22 My good friend Raymond Cheng has an updated guide: Signing Git Commits and SSH Authentication with Yubikey. 2016-03-16 some minor updates. 2015-10-27 Thanks to Dan M. For general feedback and improvements. 2015-09-29 Thanks to Tyler B. For the feedback on gpg-agent. 2015-06-29 Thanks to Eric E. For the question on signed SSH keys. By default, macOS will ask users to bind a YubiKey with valid Authentication and Encryption certificates to local user accounts. To disable this dialog and utilize the user information in the issued certificates, run the command below in Terminal to disable the smart card user pairing UI.

Hi,

Friend of mine recommended me the Royal TS software and we are evaluating it (i started with Mac OS version) at our company, but I cannot find a way to authenticate to remote SSH servers using OpenPGP private key (auth subkey) stored on the Yubikey. We are using it widely for logins into critical SSH servers by following methods listed on Yubico site (for both Win and MacOS):

https://developers.yubico.com/PGP/SSH_authentication/

Is there a way to enable sth similar ? I always get following error message which I have already seen in the terminal if the gpg-connect-agent is not running:

Load key '/Users/You/.ssh/id_rsa_yubikey.pub': invalid format

Hi Michal,

it depends on how you set up your Yubikey in macOS but it's very likely that enabling 'Run inside Login Shell' in the 'Advanced - Session' properties of your SSH connection will make it work.

Please try this first and let me know if it helps!

cheers,

felix

Hi Michal,

it depends on how you set up your Yubikey in macOS but it's very likely that enabling 'Run inside Login Shell' in the 'Advanced - Session' properties of your SSH connection will make it work.

Please try this first and let me know if it helps!

cheers,

felix

Hi Felix,

This is cool! After I enabled 'Run inside login shell' it indeed asked me for my smartcard PIN and I was able to log into the box using the pkey from Yubikey. Thanks a lot! I hope it will work the same way under Windows.

BR,

Michal

Perfect! Glad I could help!

If you need help getting this running on Windows please let us know in a new ticket.

thx,

felix

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:

Yubikey Ssh Windows

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 myVM, myResourceGroup, UbuntuLTS, azureuser, and mysshkey.pub with your own values:

How Does Ssh Authentication Work

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.

Yubikey Gpg Ssh

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.

Yubikey Ssh Mac

Next steps

• For more information on working with SSH key pairs, see Detailed steps to create and manage SSH key pairs.

• If you have difficulties with SSH connections to Azure VMs, see Troubleshoot SSH connections to an Azure Linux VM.