**Definition of Cryptography**

Cryptography is associated with the process of converting ordinary plain text into unintelligible text and vice-versa. It is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. Cryptography protects data from theft or alteration.

**History of Cryptography**

Earlier cryptography was effectively synonymous with encryption but nowadays cryptography is mainly based on mathematical theory and computer science practice.

Before the modern era, cryptography focused on message confidentiality — conversion of messages from a comprehensible form into an incomprehensible one and back again at the other end, rendering it unreadable by interceptors or eavesdroppers without the key needed for decryption of that message. Encryption attempted to ensure secrecy in communications, such as those of spies, military leaders, and diplomats. In recent decades, the field has expanded beyond confidentiality concerns to include techniques for message integrity checking, sender/receiver identity authentication, digital signatures, interactive proofs and secure computation, etc.

Though it has been used for thousands of years to hide secret messages, systematic study of cryptology as a science started around one hundred years ago. At the end of World War I, Arthur Scherbius, a German engineer invented The Enigma machine, which was a piece of spook hardware heavily used by the German forces during the World War II. Later, it was used by Britain's codebreakers as a way of deciphering German signals traffic.

**Modern Cryptography**

Modern cryptography is the cornerstone of computer and communications security. It is based on various concepts of mathematics such as number theory, computational-complexity theory, and probability theory. There are three major characteristics that separate modern cryptography from the classical approach. It operates on binary bit sequences and it relies on publicly known mathematical algorithms for coding the information. Secrecy is obtained through a secret key which is used as the seed for the algorithms. The computational difficulty of algorithms, the absence of a secret key, etc. make it impossible for an attacker to obtain the original information even if he knows the algorithm used for coding.

**Symmetric encryption**

In symmetric encryption, you use the same key for both encryption and decryption of your data or message. Both of you need to have the same key in order to encrypt and decrypt the messages that you may exchange with each other. Symmetrical encryption is an old and best-known technique. It uses a secret key that can either be a number, a word or a string of random letters. The main disadvantage of the symmetric key encryption is that all parties involved have to exchange the key used to encrypt the data before they can decrypt it.

**Asymmetric encryption**

Asymmetric encryption is quite opposite of the symmetric encryption because it doesn't use a single key but a pair of keys: a private one and a public one. You use one to encrypt your data, which is called public key, and the other to decrypt the encrypted message, which is called the private key. Your private key is yours and it must be kept private, because it is the only key that can decrypt any message that was encrypted with your public key. Public keys are public and thus no security is required - it needs to be publicly available and can be passed over the Internet. The public key is used to encrypt a message that can only be decrypted using its private counterpart.

**Conclusion**

Cryptography has played an enormous role in the shaping and development of many societies and cultures. Today, cryptography takes a new shift, new algorithms are being developed to catch up with the eavesdroppers and secure information to enhance confidentiality.

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