Cryptography is a science that has been in practice since early ages to hide secret messages. The early known evidence of use of cryptography was found the main chamber of the tomb Khnumhotep II, where some unusual hieroglyphics were used instead of the ones that are normally used. Another evidence of use of cryptography in early civilizations can be found in the book called “Arthshashtra” written by philosopher Kautilya, in which he mentioned giving spies assignments in secret messages. In ancient days cryptography was mainly used to send classified military strategies. Classic cryptography mainly uses transposition cipher, a technique in which the order of letters is rearranged for example word ‘hello’ is written as ‘hlelo’ and substitution ciphers, that systematically replace the letters with other letters. Ceasar cipher is one of the early example of a substation cipher. The substitution cipher used by Ceasar was shift by 3 where each letter is shifted by 3 places, for example letter A is replaced with letter D and letter B is replaced with letter E and follows (as shown in the figure below). The main drawback of substitution cipher is the not the encryption key rather it is the secrecy of the system, because once the system is understood the messages can be easily decrypted.  In 19th century, Hebern introduced an electro-mechanical contraption called “Herbern rotor Machine”. This machine uses a rotor with the secret key can be embedded in the rotation disc. The key embedded on the disc is used to encrypt the plain text and print the cipher text as output. After few years German Engineer Arthur Scherbius invented a device called Engima machine which was used by German forces during world war II.Cryptography was used only for military purposes until the end of second world war. Commercial application of encryption started Post world war II, when the business started trying to use cryptography to secure data from other competitors. Realizing the demand IBM introduced and cipher called Lucifer during 1970s, which was later called as Data Encryption Standard (DES) and later NIST declared DES as national standard. The problem with the DES was that it used a short encryption key, and which was broken in the year 1997. This lead to the development of Advanced Encryption Standard (AES), which was later announced as national standard for encryption by the NIST.Modern Cryptography is heavily dependent on binary mathematical calculations based on sophisticated computer algorithms where secret keys are used to encrypt and decrypt the data. There are 2 encryption algorithms that are currently in use, they are Symmetric encryption and Asymmetric encryption. Symmetric encryption is the method in which both the sender and receiver share the same key. Asymmetric encryption is the encryption algorithm that is also known as public key cryptography. It uses 2 keys, public and private key to encrypt and decrypt the data. Public key can be shared with everyone, but the private key is kept secret. Either public key and private key can be utilized in encryption of the message, but the key that’s not used in encryption has be used to decrypt the message.Now a day’s technology has made encryption a huge necessity since major financial transactions are made online and internet has become more accessible which forced the need for encryption in order in protect personal data. In fact, we use cryptography in our day to day life without even realizing it. We use a transfer protocol called HTTPS which enables SSL connection between the two nodes of communication and encrypts the data transferred using Asymmetric key encryption. Even the day to day messaging services like Facebook, whatsapp, etc., are forced to use cryptography in order to secure the zetta bytes of data being transfer daily.


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