SSH (Secure SHELL) is an open source and most trusted network protocol that is used to login into remote servers for execution of commands and programs. It is also used to transfer files from one computer to another computer over the network using secure copy (SCP) Protocol.

Deploying the public key. To use the user key that was created above, the public key needs to be placed on the server into a text file called authorizedkeys under users username.ssh. The OpenSSH tools include scp, which is a secure file-transfer utility, to help with this.

In this article we will show you how to setup password-less login on RHEL/CentOS 7.x/6.x/5.x and Fedora using ssh keys to connect to remote Linux servers without entering password. Using Password-less login with SSH keys will increase the trust between two Linux servers for easy file synchronization or transfer.

My Setup Environment

If you are dealing with number of Linux remote servers, then SSH Password-less login is one of the best way to automate tasks such as automatic backups with scripts, synchronization files using scp and remote command execution.

In this example we will setup SSH password-less automatic login from server 192.168.0.12 as user tecmint to 192.168.0.11 with user sheena.

Step 1: Create Authentication SSH-Kegen Keys on – (192.168.0.12)

First login into server 192.168.0.12 with user tecmint and generate a pair of public keys using following command.

Create SSH RSA Key

Step 2: Create .ssh Directory on – 192.168.0.11

Use SSH from server 192.168.0.12 to connect server 192.168.0.11 using sheena as user and create .ssh directory under it, using following command.

Step 3: Upload Generated Public Keys to – 192.168.0.11

Use SSH from server 192.168.0.12 and upload new generated public key (id_rsa.pub) on server 192.168.0.11 under sheena‘s .ssh directory as a file name authorized_keys.

Upload RSA Key

Step 4: Set Permissions on – 192.168.0.11

Due to different SSH versions on servers, we need to set permissions on .ssh directory and authorized_keys file.

Step 5: Login from 192.168.0.12 to 192.168.0.11 Server without Password

From now onwards you can log into 192.168.0.11 as sheena user from server 192.168.0.12 as tecmint user without password.

SSH Remote Passwordless Login

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Most authentication in Windows environments is done with a username-password pair.This works well for systems that share a common domain.When working across domains, such as between on-premise and cloud-hosted systems, it becomes more difficult.

By comparison, Linux environments commonly use public-key/private-key pairs to drive authentication.OpenSSH includes tools to help support this, specifically:

• ssh-keygen for generating secure keys
• ssh-agent and ssh-add for securely storing private keys
• scp and sftp to securely copy public key files during initial use of a server

This document provides an overview of how to use these tools on Windows to begin using key authentication with SSH.If you are unfamiliar with SSH key management, we strongly recommend you review NIST document IR 7966 titled “Security of Interactive and Automated Access Management Using Secure Shell (SSH).”

About key pairs

Key pairs refer to the public and private key files that are used by certain authentication protocols.

SSH public-key authentication uses asymmetric cryptographic algorithms to generate two key files – one 'private' and the other 'public'. The private key files are the equivalent of a password, and should protected under all circumstances. If someone acquires your private key, they can log in as you to any SSH server you have access to. The public key is what is placed on the SSH server, and may be shared without compromising the private key.

When using key authentication with an SSH server, the SSH server and client compare the public key for username provided against the private key. If the public key cannot be validated against the client-side private key, authentication fails.

Multi-factor authentication may be implemented with key pairs by requiring that a passphrase be supplied when the key pair is generated (see key generation below).During authentication the user is prompted for the passphrase, which is used along with the presence of the private key on the SSH client to authenticate the user.

Host key generation

Public keys have specific ACL requirements that, on Windows, equate to only allowing access to administrators and System.To make this easier,

• The OpenSSHUtils PowerShell module has been created to set the key ACLs properly, and should be installed on the server
• On first use of sshd, the key pair for the host will be automatically generated. If ssh-agent is running, the keys will be automatically added to the local store.

To make key authentication easy with an SSH server, run the following commands from an elevated PowerShell prompt:

Since there is no user associated with the sshd service, the host keys are stored under ProgramDatassh.

User key generation

To use key-based authentication, you first need to generate some public/private key pairs for your client.From PowerShell or cmd, use ssh-keygen to generate some key files.

This should display something like the following (where 'username' is replaced by your user name)

You can hit Enter to accept the default, or specify a path where you'd like your keys to be generated.At this point, you'll be prompted to use a passphrase to encrypt your private key files.The passphrase works with the key file to provide 2-factor authentication.For this example, we are leaving the passphrase empty.

Now you have a public/private ED25519 key pair(the .pub files are public keys and the rest are private keys):

Remember that private key files are the equivalent of a password should be protected the same way you protect your password.To help with that, use ssh-agent to securely store the private keys within a Windows security context, associated with your Windows login.To do that, start the ssh-agent service as Administrator and use ssh-add to store the private key.

After completing these steps, whenever a private key is needed for authentication from this client, ssh-agent will automatically retrieve the local private key and pass it to your SSH client.

Note

It is strongly recommended that you back up your private key to a secure location,then delete it from the local system, after adding it to ssh-agent.The private key cannot be retrieved from the agent.If you lose access to the private key, you would have to create a new key pairand update the public key on all systems you interact with.

Deploying the public key

To use the user key that was created above, the public key needs to be placed on the server into a text file called authorized_keys under usersusername.ssh.The OpenSSH tools include scp, which is a secure file-transfer utility, to help with this.

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To move the contents of your public key (~.sshid_ed25519.pub) into a text file called authorized_keys in ~.ssh on your server/host.

This example uses the Repair-AuthorizedKeyPermissions function in the OpenSSHUtils module which was previously installed on the host in the instructions above.

These steps complete the configuration required to use key-based authentication with SSH on Windows.After this, the user can connect to the sshd host from any client that has the private key.