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How to Setup Reverse SSH Tunnel on Linux

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. You'll [...]


How Port Knocking Can Add Extra Layer of Server Security

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? Computer ports can [...]


How to Setup Linux VPN Server and Client using OpenVPN

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 [...]


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 [...]


How to Encrypt and Decrypt a File using GnuPG in Linux

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. When you want to send a secret file to your friend, the first thing to do is to import your friend's [...]


Introduction to Diffie Hellman Key Exchange Algorithm

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 [...]


GnuPG Basics Explained with Linux GPG Command Examples

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. This article is part of our ongoing series on Cryptography. If you are new to [...]


Introduction to Cryptography Basic Principles

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. In a simplest form, encryption is to convert the data [...]