How to Setup Reverse SSH Tunnel on Linux

by Himanshu Arora on November 27, 2013

Reverse SSH is a technique that can be used to access systems (that are behind a firewall) from the outside world.

As you already know SSH is a network protocol that supports cryptographic communication between network nodes. Using this protocol, you can do a secure remote login, secure copy from/to a remote machine etc.

How Port Knocking Can Add Extra Layer of Server Security

by Himanshu Arora on October 3, 2013

Port Knocking technique adds an extra layer of security to your server and network, which will make it little harder for intruders to hack the system.

In this article, we’ll explain the following on a very high-level:

  • What is a port?
  • What are port attacks?
  • What is port knocking and how it helps?


How to Setup Linux VPN Server and Client using OpenVPN

by Lakshmanan Ganapathy on September 9, 2013

VPN stands for Virtual Private Network.

A Virtual Private Network enables a computer to send and receive data from one private network to another private network which are connected via public network (Internet).

This is helpful for those who are outside the company’s intranet, and like to connect to office network securely to access the internal servers. VPN is also helpful when you are connecting multiple branch offices together.

As many organizations move away from paper documents to digital documents, digital signatures are required to manage any sensitive digital documents. Digital signatures can be used to authenticate the source of the message, such that the receiver can decide whether to trust the sender or not. Now-a-days it is most widely used for software distribution and financial transactions.

In public key cryptography, it is possible to use a private key to sign a file. Anyone who has the corresponding public key can check whether the file was signed by the private key. Anyone who doesn’t have the private key cannot forge such a signature.

How to Encrypt and Decrypt a File using GnuPG in Linux

by Lakshmanan Ganapathy on February 6, 2013

Using GnuPG gpg command you can generate public and private keys. In this tutorial, we will use the keys generated by gpg command to send and receive encrypted files, and digitally sign a file.

Introduction to Diffie Hellman Key Exchange Algorithm

by Himanshu Arora on January 31, 2013

Asymmetric Encryption of data requires transfer of cryptographic private key. The most challenging part in this type of encryption is the transfer of the encryption key from sender to receiver without anyone intercepting this key in between. This transfer or rather generation on same cryptographic keys at both sides secretively was made possible by the Diffie-Hellman algorithm.

GnuPG Basics Explained with Linux GPG Command Examples

by Lakshmanan Ganapathy on October 23, 2012

GnuPG stands for GNU Privacy Guard.

GnuPG is an open implementation of OpenPGP ( Pretty Good Privacy ) standard as defined in RFC 4880. In this article we will cover the installation and the basics of generating keys using gnupg.

Introduction to Cryptography Basic Principles

by Himanshu Arora on July 18, 2012

Whenever we come across the term cryptography, the first thing and probably the only thing that comes to our mind is private communication through encryption. There is more to cryptography than just encryption. In this article, we will try to learn the basics of cryptography.