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Cryptography


Introduction

Security of data transmitted on the Internet is a very major issue. With the advent of e-Commerce, Internet Banking and various other facilities on the web, which require personal information, like Credit Card number etc, security of data transmitted over Internet has to be seriously considered.

Cryptography is the science of information security. The word is derived from the Greek "kryptos", meaning hidden. Cryptography involves providing security to data transmitted over the Internet. This is done by various means, which range from modification of data, password authentication and secure Internet protocols. Basically, before a confidential data is transmitted from the sender to a receiver over the Internet, all measures taken to ensure that none other than the receiver receives it. This is Cryptography.


Origin

The origin of Cryptography is usually dated from about 2000 BC, with the Egyptian practice of Hieroglyphics. These consisted of complex pictograms, the full meaning of which was only known to an elite few. The first known use of a modern cipher was by Julius Caesar(100 BC to 44 BC), who did not trust his messengers when communicating with his governors and officers. For this reason, he created a system in which each character in his messages was replaced by a character three positions ahead of it in the Roman alphabet.


Objectives

Modern Cryptography concerns itself with the following four objectives:

1) Confidentiality (the information cannot be understood by anyone for whom it was unintended)

2) Integrity (the information cannot be altered in storage or transit between sender and intended receiver without the alteration being detected)

3) Non-repudiation (the creator/sender of the information cannot deny at a later stage his or her intentions in the creation or transmission of the information)

4) Authentication (the sender and receiver can confirm each other's identity and the origin/destination of the information)


Process

In today's computer-centric world, Cryptography is most often associated with scrambling plaintext (ordinary text, sometimes referred to as clear-text) into cipher-text (a process called encryption), then back again (known as decryption).

The following are the usual steps associated with a normal cryptographic process:



The code of software, that is applied to the Plain-text to encrypt it; and to Cipher-text to decrypt it, is called the Key. A cryptographer will first encrypt the data. Then he will transmit this data to the receiver. The receiver will decrypt the data using a Key which has been pre-decided between the sender & receiver. This Key is known only to both of them.
So, in simple words, a key is something like a password to open or "decrypt" a secret data, known only to the Sender of the data & the Receiver.


Techniques

Cryptography includes techniques such as microdots, merging words with images, and other ways to hide information in storage or transit. For example, an international militant outfit was known to embed encrypted data within pornographic photos of a website controlled by it. A normal surfer could only see the photos & was unaware of its actual purpose. Only the person intended to decode it, was conveyed the exact photo. He, using pre-decided cryptographic technique then decoded the message from the photo.

Other techniques/procedures of encrypting messages are:


Layers

The following are the three layers in Cryptography:
Conclusion

Individuals who practice this field are known as Cryptographers. Cryptography is closely related to the disciplines of Cryptology and Cryptanalysis. Procedures and protocols that meet some or all of the above criteria are known as Cryptosystems. Cryptosystems are often thought to refer only to mathematical procedures and computer programs; however, they also include the regulation of human behaviour, such as choosing hard-to-guess passwords, logging off unused systems, and not discussing sensitive procedures with outsiders.

In recent times, Cryptography has turned into a battleground of some of the world's best mathematicians and computer scientists. The ability to securely store and transfer sensitive information has proved a critical factor in success in war and business. Because governments do not wish certain entities in and out of their countries to have access to ways to receive and send hidden information that may be a threat to national interests, Cryptography has been subject to various restrictions in many countries, ranging from limitations of the usage and export of software to the public dissemination of mathematical concepts that could be used to develop cryptosystems.

However, the Internet has allowed the spread of powerful programs and, more importantly, the underlying techniques of Cryptography, so that today many of the most advanced cryptosystems and ideas are now in the public domain.

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