What is Cryptography?

Cryptography

The art and science of concealing the messages to introduce secrecy in information security is recognized as cryptography. Cryptography is generated from two Greek word Krypto(Hidden) and grapheme(writing).

The roots of cryptography are found in Roman and Egyptian civilizations.

The earlier Roman method of cryptography, popularly known as the Caesar Shift Cipher, relies on shifting the letters of a message by an agreed number (three was a common choice), the recipient of this message would then shift the letters back by the same number and obtain the original message.

Example- the text is- hello 

In this example each letter is shifted by two digits.

Steganography

Steganography is an art of hiding data or information behind an image. Previously attacker (terrorist) used this method to send encrypted message to their person so that no one can trace what exact message is. For example hidden watermarking.

Improved coding techniques such as vigenere, Coding came into existence in the 15th century, which offered moving letters in the message with a number of variable places instead of moving them the same number of places.

Only after the 19th century, cryptography evolved from the ad hoc approaches to encryption to the more sophisticated art and science of information security.

In the early 20th century, the invention of mechanical and electromechanical machines, such as the Enigma rotor machine, provided more advanced and efficient means of coding the information.

During the period of World War II, both cryptography and cryptanalysis became excessively 

mathematical.

Cryptanalysis

The art and science of breaking the cipher text and also understanding how they work is known as cryptanalysis.

Objective of Cryptography

The primary objective of using cryptography is to provide the following four fundamental information security services.

Confidentiality (Privacy or secrecy)

Integrity (Identifying the alteration of data)

Authentication (Identification of originator)

Non repudiation (Insure that entity can’t refuse ownership)

Component of cryptography

Plain text. It is the data to be protected during transmission.

Encryption Algorithm. It is a mathematical process that produces a cipher text for any given plaintext and encryption key.

Cipher text. It is the scrambled version of the plaintext produced by the encryption algorithm using a specific the encryption key. The cipher text is not guarded. It flows on public channel. It can be intercepted or compromised by anyone who has access to the communication channel.

Decryption Algorithm, It is a mathematical process, that produces a unique plaintext for any given cipher text and decryption key. It is a cryptographic algorithm that takes a cipher text and a decryption key as input, and outputs a plain text.

Encryption Key. It is a value that is known to the sender. The sender inputs the encryption key into the encryption algorithm along with the plaintext in order to compute the cipher text.

Decryption Key. It is a value that is known to the receiver. The decryption key is related to the encryption key, but is not always identical to it. The receiver inputs the decryption key into the decryption algorithm along with the cipher text in order to compute the plaintext.

Types of Cryptography

Basically, two types of cryptography.

1. Symmetric key cryptography

2. Asymmetric key cryptography

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