Ssh Key Generation In Linux

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by conmolliate1981 2020. 9. 21. 18:27

Updated on March 30, 2020

Ssh Key Example
Ssh Key Generation In Linux Windows 10

Generating Your SSH Public Key Many Git servers authenticate using SSH public keys. In order to provide a public key, each user in your system must generate one if they don’t already have one. This process is similar across all operating systems.

Spend enough time in an IT environment and you will likely come across the term SSH keys. If you’ve already come across this IT term, then you might find yourself wondering, what are SSH keys? SSH (Secure Shell) keys are an access credential that is used in the SSH protocol.

PuTTYgen is a key generator tool for creating pairs of public and private SSH keys. It is one of the components of the open-source networking client PuTTY. Although originally written for Microsoft Windows operating system, it is now officially available for multiple operating systems including macOS, Linux.
If you or others are going to use an SSH client that requires the OpenSSH format for private keys (such as the ssh utility on Linux), export the private key: On the Conversions menu, choose Export OpenSSH key.

Read the rest of this post to learn more about what are SSH keys or consider watching webinar below to find out more about the SSH protocol and the basics of SSH authentication.

Before this post delves into an explanation on what are SSH keys, let’s take a quick look at the SSH protocol.

The SSH Protocol

The first version of the SSH protocol was developed in the summer of 1995 by Tatu Ylonen. Tatu was a researcher at the University of Helsinki when a sniffing attack was discovered on the university network. A sniffing attack intercepts and logs the traffic that takes place on a network, and can provide attackers with usernames and passwords which can then be used to gain access to critical IT assets. Thousands of credentials were impacted, including those belonging to community partnerships. This sniffing attack motivated Tatu to figure out how to make networks more secure, and this ultimately led to the creation of the SSH protocol (SSH.com).

Today, the SSH protocol is widely used to login remotely from one system into another, and its strong encryption makes it ideal to carry out tasks such as issuing remote commands and remotely managing network infrastructure and other vital system components. To use the SSH protocol, a couple pieces of software need to be installed. The remote systems need to have a piece of software called an SSH daemon, and the system used to issue commands and manage the remote servers needs to have a piece of software called the SSH client. These pieces of software are necessary to create a proper communication channel using the SSH protocol (DigitalOcean).

Essentially, SSH keys are an authentication method used to gain access to this encrypted connection between systems.

What are SSH keys?

SSH keys come in many sizes, but a popular choice is RSA 2048-bit encryption, which is comparative to a 617 digit long password. On Windows systems, it is possible to generate your own SSH key pair by downloading and using an SSH client like PuTTY. On Mac® and Linux® systems, it is possible to generate an SSH key pair using a terminal window. Watch the video below to find out how to generate your own RSA key pair on Mac and Linux.

SSH keys always come in pairs, and each pair is made up of a private key and a public key. Who or what possesses these keys determines the type of SSH key pair. If the private key and the public key remain with the user, this set of SSH keys is referred to as user keys. If the private and public key are on a remote system, then this key pair is referred to as host keys. Another type of SSH key is a session key. When a large amount of data is being transmitted, session keys are used to encrypt this information.

Now let’s take a closer look at how a private key and public key work. To keep things simple, we will focus on how user keys work.

How User Keys Work

In a user key set, the private key remains on the system being used to access the remote system and is used to decrypt information that is exchanged in the SSH protocol. Private keys should never be shared with anyone. A public key is used to encrypt information, can be shared, and is used by the user and the remote server. On the server end, the public key is saved in a file that contains a list of authorized public keys. On the user’s side, the public SSH key is stored in an SSH key management software or in a file on their computer.

Using SSH Keys

First Steps

Before you can start using SSH keys, first you need to generate your own SSH key pair on the system you would like to use to access a remote system. This article and the video mentioned above are great resources that can guide you through on how to generate an SSH key pair. Once the key pair is generated, the next step is to put the public SSH key on the remote server. Depending on your setup, this can be done by entering a couple commands in the terminal window, using JumpCloud, or by manually placing the public SSH key on the remote server (DigitalOcean).

Behind the Scenes of SSH Key Authentication

After completing the steps mentioned above, use your terminal to enter in your ssh username and the IP address of the remote system in this format: ssh username@my_ip_address. This will initiate a connection to the remote system using the SSH protocol. The protocol and specified username will then tell the remote server which public key to use to authenticate you. Then the remote server will use that public key to encrypt a random challenge message that is sent back to the client. This challenge message is decrypted using the private key on your system. Once the message is decrypted, it is combined with a previously arranged session ID and then sent back to the server. If the message matches with what the server sent out, the client is authenticated, and you will gain access to the remote server. This process proves to the server that you have the corresponding private key to the public key it has on file.

However, the security that this authentication process provides can be undermined when SSH keys are not properly managed.

Managing SSH Keys

It is imperative that proper SSH key management is in place because they often grant access to mission-critical digital assets. Also, companies tend to have a lot of SSH keys. In fact, Fortune 500 companies will often have several millions of these. Despite the difficulty in trying to manually manage millions of SSH keys, having an SSH key management system in place is continuously overlooked. SSH.com did some digging and discovered a company that had 3 million SSH keys “that granted access to live production servers. Of those, 90% were no longer used. Root access was granted by 10% of the keys, ” (SSH.com). An effective SSH key management system in place would have gone a long way in reducing this concerning security risk.

IT has a couple options to gain control over SSH keys in their environment. One of these includes using an SSH key management tool. However, this means having to manage one more platform in addition to managing an SSO provider, a directory service, and maybe a system management solution. A new solution has emerged that is providing IT with a second option: Directory-as-a-Service®.

Cloud IAM offers SSH Key Management

This cloud-based identity and access management (IAM) solution provides IT with one central place to manage SSH keys. Furthermore, IT can also centralize user authentication to Mac, Linux, and Windows systems, cloud servers, wired and WiFi networks, web-based and on-prem applications, and virtual and on-prem storage. With one central place to manage a user’s authentication to all of their resources, it becomes a simple matter of a few clicks to deprovision users from all of their resources, including SSH key access to remote systems.

Learn More about SSH Key Management with JumpCloud

For more information, consider reading this support article on how JumpCloud assists with SSH key management, or exploring this guide for a modern approach to managing user accounts on your cloud servers.
You are also more than welcome to reach out to us if you would like more information on how DaaS can simplify your SSH key management. If you’re ready to start testing our modern IAM platform, sign up for a free account. You’ll be able to explore all of our features, and your first ten users are free forever.

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This article describes ways to generate and use secure shell (SSH) keys on a Windows computer to create and connect to a Linux virtual machine (VM) in Azure. To use SSH keys from a Linux or macOS client, see the quick or detailed guidance.

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.

Ssh Key Generation In Linux

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.

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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.

Windows packages and SSH clients

You connect to and manage Linux VMs in Azure using an SSH client. Computers running Linux or macOS usually have a suite of SSH commands to generate and manage SSH keys and to make SSH connections.

Windows computers do not always have comparable SSH commands installed. Recent versions of Windows 10 provide OpenSSH client commands to create and manage SSH keys and make SSH connections from a command prompt. Recent Windows 10 versions also include the Windows Subsystem for Linux to run and access utilities such as an SSH client natively within a Bash shell.

Ssh Key Example

Other common Windows SSH clients you can install locally are included in the following packages:

Cross site request forgery definition. You can also use the SSH utilities available in Bash in the Azure Cloud Shell.

Access Cloud Shell in your web browser at https://shell.azure.com or in the Azure portal.
Access Cloud Shell as a terminal from within Visual Studio Code by installing the Azure Account extension.

Create an SSH key pair

The following sections describe two options to create an SSH key pair on Windows. You can use a shell command (ssh-keygen) or a GUI tool (PuTTYgen). Also note, when using Powershell to create a key, upload the public key as ssh.com(SECSH) format. When using CLI, convert the key into OpenSSH format prior to uploading.

Create SSH keys with ssh-keygen

If you run a command shell on Windows that supports SSH client tools (or you use Azure Cloud Shell), create an SSH key pair using the ssh-keygen command. Type the following command, and answer the prompts. If an SSH key pair exists in the chosen location, those files are overwritten.

For more background and information, see the quick or detailed steps to create SSH keys using ssh-keygen.

Create SSH keys with PuTTYgen

If you prefer to use a GUI-based tool to create SSH keys, you can use the PuTTYgen key generator, included with the PuTTY download package.

To create an SSH RSA key pair with PuTTYgen:

Start PuTTYgen.
Click Generate. By default PuTTYgen generates a 2048-bit SSH-2 RSA key.
Move the mouse around in the blank area to provide randomness for the key.
After the public key is generated, optionally enter and confirm a passphrase. You will be prompted for the passphrase when you authenticate to the VM with your private SSH key. Without a passphrase, if someone obtains your private key, they can sign in to any VM or service that uses that key. We recommend you create a passphrase. However, if you forget the passphrase, there is no way to recover it.
The public key is displayed at the top of the window. You can copy this entire public key and then paste it into the Azure portal or an Azure Resource Manager template when you create a Linux VM. You can also select Save public key to save a copy to your computer:
Optionally, to save the private key in PuTTy private key format (.ppk file), select Save private key. You will need the .ppk file later to use PuTTY to make an SSH connection to the VM.

If you want to save the private key in the OpenSSH format, the private key format used by many SSH clients, select Conversions > Export OpenSSH key.

Provide an 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 or other methods.

The following example shows how you would copy and paste this public key into the Azure portal when you create a Linux VM. The public key is typically then stored in the ~/.ssh/authorized_key directory on your new VM.

Connect to your VM

One way to make an SSH connection to your Linux VM from Windows is to use an SSH client. This is the preferred method if you have an SSH client installed on your Windows system, or if you use the SSH tools in Bash in Azure Cloud Shell. If you prefer a GUI-based tool, you can connect with PuTTY.

Use 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 configured a passphrase when you created your key pair, enter the passphrase when prompted during the sign-in process.

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.

Connect with PuTTY

If you installed the PuTTY download package and previously generated a PuTTY private key (.ppk) file, you can connect to a Linux VM with PuTTY.

Start PuTTy.
Fill in the host name or IP address of your VM from the Azure portal:
Select the Connection > SSH > Auth category. Browse to and select your PuTTY private key (.ppk file):
Click Open to connect to your VM.

Next steps