**What is Cryptography?**

Cryptography means the art or the science of writing secret messages. The original message or text before going to any process is called plain text or clear text. The process of changing plain text into a secret form is called encryption. Once the original text has been encrypted, the resultant text is known as cipher text or cryptogram. The process of converting cipher text into plain text is known as decryption. Mostly nowadays, in an encryption process, some mathematical algorithms are used. Basically, the encryption algorithm is the set of instructions that have a particular method of encrypting plain text into cipher text.

For the encryption process, cryptography includes the use of concealed messages, codes, and codebooks. In conceal messages, the plain text is written with invisible ink. This invisible ink is usually lemon or orange juice. When it is dry, it looks like plain paper, but if you put this paper in sunlight or pressed by iron, the message is prominently shown on that paper. There is a preset order codebook made, in which, numbers, symbols, or letters, rearranged by another number or letter, are used and a coded message is written, which is secured for a small-time period.

**Why do we need Cryptography?**

Cryptography protects the world’s banking systems as well, which is the requirement of today’s world. Many banks and other financial institutions conduct their business over open switched networks like the Internet. Without the ability to protect bank transactions and communications, criminals could interfere with the transactions and rob banks without a trace. It plays an important role in secure communication. For example, communications over telephone lines including faxes and e-mail messages, financial transactions, medical histories, e-banking, and even other types of important information need a secure communication medium. Sometimes, the medium is hacked by intruders and gets all of your pieces of information.

**Types of Cryptography**

**Symmetric key cryptography **

An encryption system in which sender and receiver use a message share a single key for both encryption and decryption of data. This is known as symmetric-key cryptography. The most popular symmetric-key cryptographic system is the Data Encryption Standard (DES). The keys may be identical or there might be a simple transformation to go between the two keys. Symmetric key cryptography sometimes is also called secret-key cryptography. The list of ciphers used in Secret key cryptography is listed below:

**Transposition Cipher**

In cryptography, a transposition cipher is a method of encryption. This is where the positions held by the unit plain texts (which are characters or group of characters get shifted according to a regular system. In this way, the ciphertext constitutes a permutation of plain text.

**Substitution Cipher**

A substitution cipher is a method of encrypting. These units of plain text get replaced with ciphertexts according to a fixed system. The units may be single letters, a pair of letters, triplets, and so on.

**Stream Cipher**

A stream cipher is a secret key encryption algorithm. In this, bits are encrypted a single bit at a time. With a stream cipher, the same plain text bit or byte will encrypt to a different bit or byte every time it is encrypted

**Block Cipher**

A block cipher is an encryption method. This method applies a deterministic algorithm along with a symmetric key to encrypt a block of text; Rather than encrypting a single bit at a time like a stream cipher.

**Asymmetric key cryptography**

Asymmetric cryptography is also known as Public key cryptography. It is crptographic system that uses pair of keys. First is public key which is emanated widely. Second is private key which are only known to the owner. This accomplishes two functions. Firstly authentication, where the public key verifies the pair holder of its corresponding private key. The only private key owner can decrypt the message encrypted with a public key. In public key system, any person can encrypt the message with reciever’s public key. In practical, the generation of public and private key pair must be computationally economical. The strength of public key cryptographic system relies on the computational efforts. This is required in order to authenticate the public key with its corresponding private key. Asymmetric key cryptography gives much more security than private key system.