Cryptography is the study of secure communications techniques that allow only the sender and intended recipient of a message to view its contents. The term is derived from the Greek word kryptos, which means hidden.
Features Of Cryptography
Confidentiality: Information can only be accessed by the person for whom it is intended and no other person except him can access it.
Integrity: Information cannot be modified in storage or transition between sender and intended receiver without any addition to information being detected.
Non-repudiation: The creator/sender of information cannot deny his or her intention to send information at later stage.
Authentication: The identities of sender and receiver are confirmed. As well as destination/origin of information is confirmed.
Types Of Cryptography
In general there are three types Of cryptography:
Symmetric Key Cryptography
It is an encryption system where the sender and receiver of message use a single common key to encrypt and decrypt messages. Symmetric Key Systems are faster and simpler but the problem is that sender and receiver have to somehow exchange key in a secure manner. The most popular symmetric key cryptography system is Data Encryption System(DES).
There is no usage of any key in this algorithm. A hash value with fixed length is calculated as per the plain text which makes it impossible for contents of plain text to be recovered. Many operating systems use hash functions to encrypt passwords.
Asymmetric Key Cryptography
Under this system a pair of keys is used to encrypt and decrypt information. A public key is used for encryption and a private key is used for decryption. Public key and Private Key are different. Even if the public key is known by everyone the intended receiver can only decode it because he alone knows the private key.