Skip to main content

Hardening SSH Security in Linux

SSH is a popular network protocol used to access remote computers through certain networks or the internet. OpenSSH is an application that provides SSH accessibility for a computer or server. A common method used to start a communication with SSH access is by providing a username and password before a secured connection is established. This method is not really safe because you provide credentials in plain text and transfer them through the network. It also makes it any scumbag individuals be easier to guess your password or perform a brute force attack in order to gain your server access. There are several possible ways that I think can be used for hardening your SSH security.
  1. Disable root access
  2. Change SSH port number
  3. Utilize RSA authentication
  4. Disable plain password login

Disable root access

1) Before you disable the root access, you need to make sure that there is another user account on your remote computer.

2) Create a new user as needed.
$ adduser youruser
3) Edit SSH configuration in /etc/ssh/sshd_config. Set new values for several following properties.
PermitRootLogin no
AllowUsers youruser
AllowUsers property is optional. It is used only for limiting access to certain users. You can add more users by separating it using space in the value.

4) Restart SSH service.
$ service sshd restart

Change SSH Port Number

You can change Port property other than 22.

Utilize RSA Authentication

1) Generate private and public keys in your local computer. I prefer to use PuTTYgen because it can generate not only an OpenSSH-compatible key but also a PuTTY-compatible key. PuTTY is a common application for remote access available for Windows. It needs a certain format of the private key with .PPK extension. PuTTYgen is included in PuTTY installation.

2) Open PuTTYgen. Set the number of bits in the generated key (2048, 4096, etc). Click "Generate".

3) After the process was completed, you can get 4 types of keys. First, in the big text box, it is an OpenSSH-compatible public key. Copy the content, paste it to a text editor (e.g. Notepad) and save it as Second, you possibly need to fill in the key passphrase. It adds more security to your private key. Click "Save public key" and save it as Third, click "Save private key" and save as id_rsa.ppk. It's PuTTY-compatible private key. Fourth, choose the "Conversion" menu then choose the "Export OpenSSH key". It will generate an OpenSSH-compatible private key and save it as id_rsa.

4) Now, back to the OpenSSH configuration in the remote server. Set new values for several following properties.
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile %h/.ssh/authorized_keys
The last property means that the OpenSSH application will check any allowed public keys stored in the user authorized_keys file.

5) Copy your user OpenSSH-compatible public key content and append it to /home/[yur_user]/.ssh/authorized_keys. The .ssh directory should be owned by your user and set its mode to 0700 for security while the authorized_keys mode should be 0600.

6) Back to the local computer and open your PuTTY application. On the Session menu, insert your remote computer address with its user and port. Then, go to Auth menu, choose your PuTTY-compatible private key. Then, back to the Session menu and save your configuration.

Disable plain password login

Before you implement this configuration, you must make sure that the previous process is working. By setting PasswordAuthentication value to "no" will make your server can be accessed only by RSA authentication.

If you think this article is useful, you can share it. Or, if you have any suggestions or questions, please leave them in the comment below.


Popular posts from this blog

Setting Up Next.js Project With ESLint, Typescript, and AirBnB Configuration

If we initiate a Next.js project using the  create-next-app tool, our project will be included with ESLint configuration that we can apply using yarn run lint . By default, the tool installs eslint-config-next and extends next/core-web-vitals in the ESLint configuration. The Next.js configuration has been integrated with linting rules for React and several other libraries and tools. yarn create next-app --typescript For additional configuration such as AirBnB, it is also possible. First, we need to install the peer dependencies of eslint-config-airbnb . We also add support for Typescript using eslint-config-airbnb-typescript . yarn add --dev eslint-config-airbnb eslint-plugin-import eslint-plugin-jsx-a11y eslint-plugin-react eslint-plugin-react-hooks yarn add --dev eslint-config-airbnb-typescript @typescript-eslint/eslint-plugin @typescript-eslint/parser After that, we can update the .eslintrc.json file for the new configuration. { "extends": [ "airb

Rangkaian Sensor Infrared dengan Photo Dioda

Keunggulan photodioda dibandingkan LDR adalah photodioda lebih tidak rentan terhadap noise karena hanya menerima sinar infrared, sedangkan LDR menerima seluruh cahaya yang ada termasuk infrared. Rangkaian yang akan kita gunakan adalah seperti gambar di bawah ini. Pada saat intensitas Infrared yang diterima Photodiode besar maka tahanan Photodiode menjadi kecil, sedangkan jika intensitas Infrared yang diterima Photodiode kecil maka tahanan yang dimiliki photodiode besar. Jika  tahanan photodiode kecil  maka tegangan  V- akan kecil . Misal tahanan photodiode mengecil menjadi 10kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 10 / (10+10) x Vcc V- = (1/2) x 5 Volt V- = 2.5 Volt Sedangkan jika  tahanan photodiode besar  maka tegangan  V- akan besar  (mendekati nilai Vcc). Misal tahanan photodiode menjadi 150kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 150 / (150+10) x Vcc V- = (150/160) x 5

Itachi Uchiha

The Real Hero of Konoha

How To Use Git in Netbeans

Git is a popular version control application nowadays. Recently I have created a note about its differences with SVN and how to use it in Eclipse . There are many Git client tools. But I just want to show how to use Netbeans built-in Git tools. It makes the development process easier because it has been integrated with the IDE. Create Remote Git Repository We need a remote Git repository so everyone can store or receive any revision or updated files through the networks. We can set up our own Git server or use a public Git server like Github . In this note, I use Github. 1. Create an account in Github and create an empty Git repository Create an empty public repository in Github 2. Get the remote repository link Your Github Repository URL Create a New Project in Netbeans and Create Local Git Repository After we have a remote Git repository, we can create a project stored in the remote repository. We also need to create a local repository before we can push

Raspberry Pi Bluetooth Connection

Raspberry Pi 3 provides a built-in Bluetooth module. The latest Raspbian has been bundled with tools for enabling Bluetooth connection. The Bluetooth icon will be shown up on the top right corner of the desktop. It's a tool to discover available Bluetooth devices and connect Pi with Bluetooth devices. It is easy to connect any Bluetooth-enabled electronic device with Pi. But, sometimes Pi will fail to connect, especially for Bluetooth device that has no standardized services. From a terminal, we can use the  bluetoothctl tool to scan and connect with a Bluetooth device. You should make sure that the BlueZ protocol stack has been installed by running $ apt-get install bluez Run bluetoothctl to enter the tool command window Turn the power on by running power on (Optional) You can set AutoEnable=true in /etc/bluetooth/main.conf if you want to make the Bluetooth auto power-on after reboot. Run devices to see which devices have been paired Run scan on if your desired d

Configuring Swap Memory on Ubuntu Using Ansible

If we maintain a Linux machine with a low memory capacity while we are required to run an application with high memory consumption, enabling swap memory is an option. Ansible can be utilized as a helper tool to automate the creation of swap memory. A swap file can be allocated in the available storage of the machine. The swap file then can be assigned as a swap memory. Firstly, we should prepare the inventory file. The following snippet is an example, you must provide your own configuration. [server] [server:vars] ansible_user=root ansible_ssh_private_key_file=~/.ssh/id_rsa Secondly, we need to prepare the task file that contains not only the tasks but also some variables and connection information. For instance, we set /swapfile  as the name of our swap file. We also set the swap memory size to 2GB and the swappiness level to 60. - hosts: server become: true vars: swap_vars: size: 2G swappiness: 60 For simplicity, we only check the exi