Sec-Art: SSH

Showing posts with label SSH. Show all posts

What is Banner Grabbing : Banner Grabbing for Beginners

Banner grabbing is a technique used to gain information about a computer system on a network and the services running on its open ports. An Attacker can use banner grabbing in order to find network hosts that are running versions of applications and operating systems with known exploits. Some examples of service ports used for banner grabbing are those used by Hyper Text Transfer Protocol (port 80), File Transfer Protocol (port 21), and Simple Mail Transfer Protocol (port 25). Banners can be accessed through Client softwares like netcat, telnet in the command prompt on the target system’s IP address. Other tools for banner grabbing include Nmap, SuperScan etc. For example, to grab a banner, we can establish a connection to a target web server using Netcat, then send an HTTP request. The response will typically contain information about the service running on the host.

How to reconnect to a disconnected ssh session on Linux based SSH Server

Whenever we run a very long jobs on server over ssh, then sometimes the ssh-session will disconnected for various reasons. And when we again try connect to the server, then it will start another ssh-session. Now at that situation reconnect to a disconnected ssh session with the help of tmux utility. tmux is a terminal multiplexer, which can be used to multiplex several virtual consoles, allowing a user to access multiple separate terminal sessions inside a single terminal window or remote terminal session. It is useful for dealing with multiple programs from a command-line interface, and for separating programs from the Unix shell that started the program. First install tmux in your system if it not installed.

 $ sudo apt-get install tmux

So, in order to make your ssh-session capable to reconnect, first connect to your ssh-server

How to Set up SSH keys on a Linux based Client/Server

An SSH key is an access credential in the SSH protocol. Its function is similar to that of user names and passwords, but the keys are primarily used for automated processes and for implementing single sign-on by system administrators and power users. SSH keys provide a more secure way of logging into servers with SSH than using a password alone. While a password can eventually be cracked with a brute force attack, SSH keys are nearly impossible to decipher by brute force alone. Generating a key pair provides user with two long string of characters: a public and a private key. So we can place the public key on any server, and then unlock it by connecting to it with a client that already has the private key. When the two match up, the system unlocks without the need for a password. We can increase security even more by protecting the private key with a passphrase. So lets get start.

A Beginners Guide To SSH : How to start with SSH

The most common way of connecting to a remote Linux server is through SSH (aka Secure Shell). SSH is a secure protocol used as the primary means of connecting to Linux servers remotely. It provides a text-based interface by spawning a remote shell. After connecting, all commands you type in your local terminal are sent to the remote server and executed there. SSH uses public key cryptography for both connection and authentication. SSH is the default tool for system administrator to perform various tasks on servers remotely. In order to use SSH to access your server remotely, you will need a SSH client on your local machine. For Linux machines ssh-client is comes with built-in, and for windows machine you can use putty : https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html here.

How to install OpenSSH Server on Ubuntu Linux 16.04

First update repository and upgrade system

    sudo apt-get update
    sudo apt-get upgrade

now install open-ssh server

    sudo apt-get install openssh-server

then check the status of ssh service by

    sudo service ssh status