Python for Cybersecurity: Building a Basic Port Scanner

Table of Contents

  1. Introduction
  2. Prerequisites
  3. Setup
  4. Building the Port Scanner
  5. Executing the Port Scanner
  6. Conclusion

Introduction

In today’s digital landscape, cybersecurity plays a vital role in safeguarding systems and networks. A fundamental aspect of cybersecurity is the ability to scan network ports to identify potential vulnerabilities. In this tutorial, we will explore how to build a basic port scanner using Python. By the end of this tutorial, you will have a solid understanding of how port scanning works and a working port scanning tool that you can use for basic security assessments.

Prerequisites

To follow along with this tutorial, you should have a basic understanding of Python programming. Familiarity with network protocols, such as TCP/IP, will also be helpful but is not mandatory. Additionally, you will need to have Python installed on your machine.

Setup

Before diving into the code, we need to install the necessary libraries. In this tutorial, we will be using the socket library, which provides low-level network communication capabilities. To install it, open your terminal or command prompt and run the following command: python pip install socket With the socket library installed, we can now proceed to build our port scanner.

Building the Port Scanner

  1. Start by creating a new Python file called port_scanner.py.

  2. Open the file in your favorite text editor and import the socket library:

    import socket

  3. Next, define a function called scan_port that will accept the target IP address and a port number as parameters:

    def scan_port(target_ip, port):
    # Code to be added

  4. Inside the scan_port function, create a new socket object:

    def scan_port(target_ip, port):
    # Create a new socket object
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    The socket.AF_INET parameter specifies the address family, and socket.SOCK_STREAM specifies the socket type for TCP connections.

  5. Before attempting to scan the port, we need to handle potential exceptions. Add a try-except block:

    def scan_port(target_ip, port):
    try:
        # Create a new socket object
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

        # Code to be added

    except socket.error as e:
        print(f"Error: {e}")

    This will catch any socket-related errors that may occur during the port scanning process.

  6. Within the try block, use the connect method to attempt a connection to the target IP address and port:

    def scan_port(target_ip, port):
    try:
        # Create a new socket object
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

        # Attempt a connection to the target IP address and port
        result = s.connect_ex((target_ip, port))

    except socket.error as e:
        print(f"Error: {e}")

    The connect_ex method returns an error code. If the connection is successful, the error code will be 0.

  7. Add a conditional statement to check the result of the connection attempt:

    def scan_port(target_ip, port):
    try:
        # Create a new socket object
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

        # Attempt a connection to the target IP address and port
        result = s.connect_ex((target_ip, port))

        # Check the result of the connection attempt
        if result == 0:
            print(f"Port {port} is open")
        else:
            print(f"Port {port} is closed")

    except socket.error as e:
        print(f"Error: {e}")

    If the error code is 0, we print a message indicating that the port is open. Otherwise, we print a message indicating that the port is closed.

  8. Save the file. Our basic port scanner is now complete!

Executing the Port Scanner

To execute the port scanner and scan a target IP address for open ports, follow these steps:

  1. Open a terminal or command prompt.

  2. Navigate to the directory where you saved the port_scanner.py file.

  3. Run the following command, replacing target_ip with the IP address you want to scan and port with the port number:

    python port_scanner.py target_ip port

    For example, to scan port 80 on the IP address 192.168.0.1, you would run the following command:

    python port_scanner.py 192.168.0.1 80

  4. The port scanner will attempt a connection to the specified IP address and port. The output will indicate whether the port is open or closed.

Conclusion

In this tutorial, we have learned how to build a basic port scanner using Python. We started by setting up the necessary libraries and then proceeded to write the code for the port scanner. Finally, we executed the port scanner and scanned a target IP address for open ports. Port scanning is an essential technique in the field of cybersecurity, allowing us to identify potential entry points into a system or network. However, it is crucial to use port scanning tools responsibly and with proper authorization.

You now have a solid foundation for building upon this basic port scanner. Consider adding additional features, such as the ability to scan multiple ports or an entire range of IP addresses. Happy coding!

Published:

Related Articles