**Classical Cryptography –**

The earliest known use of Cryptography can be dated back to 1900 BCE during the time of Old Kingdom of Egypt in form of non-standard hieroglyphs. Hieroglyphs were a secret form of communication that the Egyptians used to communicate with one another. This secret text was known only to the scribes of the kings who used to transmit messages on their behalf.

The ancient Greeks were well known for the use of Ciphers. The Caesar Cipher or Shift Cipher is one of the earliest and simplest well-known cryptographic technique. It is a form of Substitution Cipher where each character in a word is replaced by a fixed number of positions. For example with a shift of 3, A is replaced by D, B by E and so on.

**During World Wars –**

Cryptography played a vital in the victory of Allied forces during World War I and World War II. World War II prominently saw the use of electromechanical cipher machines. The story of Allied victory over the Germans by cracking the world-famous Enigma machine is well known. Like all rotor machines, Enigma is a combination of electro-mechanical subsystems. It consisted of somewhat three to five rotors. Whenever, a key was pressed, one or more rotors rotated on the spindle and accordingly the key was *scrambled* to something else.

**Data Encryption Standard (DES) –**

In early 1970s, Data Encryption Standard or DES came into existence. It is a symmetric-key algorithm based on *Feistel cipher* and is used for the encryption of electronic data. It has a relatively small key size of 56-bits and encrypted 64 bits or 8 characters at a time. But, it was later discontinued as it was found to be insecure especially against brute force attacks cause of its relatively small key size.

**Advance Encryption Standard (AES) –**

The DES was replaced by Advance Encryption Standard or AES in 2001. Unlike DES, AES is based on *substitution-permutation network*. AES is a sub-set of Rijndael. It is a family of ciphers with different key and block sizes. In case of AES, the block size is 128 bits or 16 characters which means 16 characters can be encrypted at a time. It comes with three different key size variants: 128 bits, 192 bits and 256 bits.

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