1. Ssh Generate Key Ubuntu
2. Rhel 7 Generate Ssh Host Keys
3. Rhel Generate Ssh Host Keys List
4. Create Ssh Key Linux
5. Redhat Regenerate Ssh Host Keys

• Dec 18, 2019  Using SSH keys is generally more secure and convenient than traditional password authentication. This tutorial explains how to generate SSH keys on CentOS 7 systems. We will also show you how to set up an SSH key-based authentication and connect to your remote Linux servers without entering a password. Creating SSH keys on CentOS #.
• Ssh-copy-id -i /.ssh/mykey user@host This logs into the server host, and copies keys to the server, and configures them to grant access by adding them to the authorizedkeys file. The copying may ask for a password or other authentication for the server.
• Nov 24, 2010 When I clone an OS image to a new, identical hardware PC I of course need to change the host name in a couple of places on the new machine. I suspect it is also good practice to generate new ssh keys for use by openssh server.
• Red Hat Enterprise Linux 6 uses SSH Protocol 2 and RSA keys by default (see Section 14.1.3, “Protocol Versions” for more information). Important Do not generate key pairs as root, as only root would be able to use those keys.
• The authenticity of host xxx can't be established If you have logged into the VPS via SSH in the past, after you regenerate the hostkeys for a new SSH connection you should get a message stating that the authenticity of the server cannot be established. This is true, because the server's fingerprint is stored in a local cache on your system: On.

When you install a fresh system, then at the start of the ssh service, it generates the host keys for your system which later on used for authentication. But if due to some reason you need to generate the host keys, then the process is explained below.

This tutorial explains how to configure and manage SSH Server and SSH Client in Linux step by step with practical examples. Learn how to install, enable and start SSH Server and SSH client; generate SSH public keys and SSH private keys for key based authentication and configure User and Host Based Security in detail.

As a Linux administrator you should know

• SSH stand for Secure Shell.
• SSH is a network protocol for secure data communication.
• SSH protocol allows remote command line login.
• SSH protocol enables remote command execution.
• To use SSH you need to deploy SSH Server and SSH Client program respectively.
• OpenSSH is a FREE version of the SSH.
• Telnet, rlogin, and ftp transmit unencrypted data over internet.
• OpenSSH encrypt data before sending it over insecure network like internet.
• OpenSSH effectively eliminate eavesdropping, connection hijacking, and other attacks.
• OpenSSH provides secure tunneling and several authentication methods.
• OpenSSH replace Telnet and rlogin with SSH, rcp with scp, ftp with sftp.

SSH Tools

For RHCE exam you should know following SSH tools

sshd

The daemon service that implements the ssh server. By default it must be listening on port 22 TCP/IP.

ssh

The ssh [ Secure Shell command ] is a secure way to log and execute commands in to SSH Server system.

scp

The Secure Copy command is a secure way to transfer files between computers using the private/public key encryption method.

ssh-keygen

This utility is used to create the public/private keys.

ssh-agent

This utility holds private keys used for RSA authentication.

ssh-add

Adds RSA identities to the authentication agent ssh-agent.

Labs exercises

• Configure a SSH server and SSH client on RHEL.
• Create two user user1 and user2 and verify that both users can login in SSH server from SSH client.
• Do not allow root and user1 users to login to it and allow the rest of users. To confirm it login from user2.
• Re-configure SSH Server to allow login only using public / private keys. Generate keys for user2 and verify that user2 can login using keys.
• Change default ssh port to 2223

In this tutorial I will use two systems Server and linuxclient from our LAB environment. I will configure OpenSSH Server on Server system and OpenSSH client on linuxclient system. If you want to check the network topology used in this article please check following article. Lab set up for RHEL practice.

LAB Exercise solutions

How to configure SSH Server in RHEL

Two RPM are required to configure and run OpenSSH server.

• openssh-server
• openssh

Before you start configuration make sure that you have necessary RPM packages installed. Install if any RPM is missing.

Check the current status of sshd service, it must be running. If service is stopped start it. Options you need with service command are startstoprestartstatus

Configure it to start when the system is booted

IP address of OpenSSH server is required, note it down

In RHCE exam you need to configure a firewall to either block or allow network communication through one or more ports. So if you have configured firewall then you have to allow SSH.

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That all setting which we need on server.

How to configure SSH client on RHEL 6

openssh-clients rpm is required for ssh client.

Check necessary RPM, install if any missing

Check sshd service status it must be running. Start it if it is off

Configure sshd service to start to at boot time

Check connectivity from SSH server

That's all setting which we need on client system.

Create two user user1 and user2 and verify that both users can login in SSH server from SSH client.

Go on server and create two users user1 and user2

Open main configuration file sshd_config

Check the value of PasswordAuthentication directive. In order to accept local user password base authentication it must be set to yes. Set it to yes if it is set to no and save the file.

Restart the service if you have made any change in sshd_config

Go on linuxclient system and verify that both users can login in SSH server. Also verify from root user.

Do not allow root and user1 users to login to it and allow the rest of users. To confirm it login from user2.

User and Host Based Security

Following additional directives can be added to /etc/sshd/sshd_config file in order to make the ssh server more restrictive.

Block empty passwords

Block root user to log on the system using ssh.

Limit the users allowed to access a system via SSH. In this case only users 'laxmi' and 'vinita' are allowed to login on the system using SSH

Make it more restrictive and add node address with user name. In following case only allow login through SSH users 'laxmi' and 'vinita' from 192.168.1.10 node.

In addition you can restrict the access to users. In this case all users except 'user1' are allowed to connect to the SSH server.

Go back on server and open main configuration file again

In the end of file add following directives and save the file

Restart the sshd service

Go back on linuxclient system and verify that we have blocked user1 and root. Also verify that user2 able to login in SSH server.

Re-configure SSH Server to allow login only using public / private keys. Generate keys for user2 and verify that user2 can login using keys.

To make Linux server more secure linux administrator usually disable password authentication on the SSH server and allow only public/private keys authentication.

Private Keys

Private keys are stored on server and must be secured. Anything encrypted with public key can only be decrypted with paired private key. So it must be accessible only to the user owner of that key, in the .ssh subdirectory of that user's home directory.

Public Keys

Public keys are publicly available. Public keys are required to connect with server. The public keys for SSH servers belong on administrative workstations.

Go back on server and open main configuration file again

Uncomment following directives and save the file

Restart the sshd service

Login form user2 and create a ssh directory with permission 755

Come back on linuxclient system and create a normal user account user2.

Login form user2 and create a ssh directory with permission 755

Generate the public/private key pair. Accept default location for key file.

Enter passphrase 'I love linux' and confirm

Public key is stored in /home/user2/.ssh/id_rsa.pub. Create a copy of public key

Copy the authorized_keys file on server to /home/user2/.ssh/authorized_keys. Enter user2 [user account on server] password when asked

On server verify that we have successfully copied public key on server. Also set permission to 644 for authorized_keys

Login from root on server and open sshd_config file

Set PasswordAuthentication directive to no and save the file. This will block login using password.

Restart the sshd service

Come back on linuxclient system.

Logout from user2 and login back.

Now try to login from user2 on linuxclient. Enter passphrase 'I love linux'

Ssh Generate Key Ubuntu

Come on server and open sshd_config file again

Uncomment following directive and change value to 2223

restart the sshd service

Go back on linuxclient system and try to connect with default port

Now specify the new port

SSH Configuration files

There are two different sets of configuration files

• System-wide SSH configuration :- stored in the /etc/ssh/ directory
• User-specific SSH configuration :- stored in ~/.ssh/ within the user's home directory

System-wide configuration files

User-specific configuration files

Rhel 7 Generate Ssh Host Keys

This is an unusual topic since most distribution create these keys for you during the installation of the OpenSSH server package. But it may be useful to be able generate new server keys from time to time, this happen to me when I duplicate Virtual Private Server which contains an installed ssh package.

OpenSSH require different keys depending if you use SSH1 and/or SSH2 protocol. All keys are generated by ssh-keygen, that one should be available on your system with the ssh package. The receipt is almost the same as for generating your own keys, except that you should use an empty passphrase. Default key lengths are also appropriate (2048 bits for rsa and 1024 bits for dsa)

SSH1 protocol

Rhel Generate Ssh Host Keys List

For SSH1 protocol, you need a rsa1 key generated has follow:

SSH2 protocol

Create Ssh Key Linux

For SSH2 protocol, you need two keys, one RSA key and one DSA key generated has follow:

Redhat Regenerate Ssh Host Keys

Since January 2011, OpenSSH also support ECDSA key, you may generate a new one using: