Posted by : Paras Sharma Friday, 18 December 2015

Cryptography basically means making and breaking code. It is a practice and study of techniques for secure communication in the presence of third parties. In modern times cryptography has got its applications in ATM, passwords, E-commerce etc.
But from where it originated? To learn about that let’s go back in the past. We get the trace of first crypto science in ancient India during 683 CE. Also ancient Egypt, China, Greeks were also profound in crypto science

An Example of Ancient Cryptography:

            Gopibhagya madhuvrata srngisodadhisandhiga I
Khalajivitakhatava galahalarasandhara II
This shloka, a hymn to Lord Krishna or Shiva, gives the value of pi upto 31 decimal places. 
ga - 3 pii - 1 bhaa - 4 gya - 1 ma - 5 dhu - 9 ra - 2 ta -6 shru - 5 ga - 3 sho - 5 da - 8 dhi - 9 sa - 7 dha - 9ga - 3 kha - 2 la - 3 jii - 8 vi - 4 ta - 6 kha - 2 ta - 6 va - 4 ga - 3 la - 3 ra - 2 sa - 7 dha - 9 ra – 2

pi = 3.1415926535897932384626433832792

Katapayadi system is used to encode numbers in many shlokas
To remember the value of pi upto 31 decimal places cryptography techniques were used by Ancient India.

Over two thousand years ago, Roman Emperor Julius Caesar invented a simple cipher system to send secret messages to his officers in the field. The Caesar Cipher shifts the alphabet forward three places to create a new alphabet for sending secret messages.
Standard Alphabet:
Caesar Alphabet:
EXAMPLE: The message THE ENEMY IS NEAR would be written
QEB BKBJV FP KBXO using the Caesar Cipher system.

Modern Cryptography
As the Internet and other forms of electronic communication become more prevalent, electronic security is becoming increasingly important. Cryptography is used to protect e-mail messages, credit card information, and corporate data.
In modern days cryptography has become securing information from an eve. More generally, cryptography is about constructing and analyzing protocols that block Eve (or adversaries); various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, and electrical engineering.

To understand the modern Cryptography we need to understand some of the terms:

 Cipher: A mapping algorithm that is applied to a fixed number of characters at a time with an intent of concealing the contents of the message.

Code: A mapping algorithm that is applied to a variable number of characters (according to linguistic entities) at a time with intent of concealing the contents of the message.

Cryptanalysis: The study of methods of reading enciphered and encoded messages without original knowledge of the cipher method used or the current keys.

Cryptography: The study of methods of enciphering and deciphering messages to conceal the contents of a message.

Cryptology: The study of both cryptography (enciphering and deciphering) and cryptanalysis (breaking or cracking a code system or individual messages).

Deciphering: The procedure of turning enciphered text into plain text with prior knowledge of the algorithms or keys involved. This is what the intended message receiver does.

Decryption: The science of turning enciphered text into plain text without prior knowledge of the algorithms or keys involved. This is what the interceptor or 'cracker' does.

Modern Cryptography can be divided into many types:

           Secret key cryptography: All codes are a bit like padlocks. You "lock" your message, the message travels to its destination, and then the recipient "unlocks" it and reads it. But not all codes work the same way.
Suppose you're an agent working in New Delhi, India and you need to send a message to another agent in Mumbai, India. The best way to do it is for the two of you to meet up in advance, in person, and agree on a method of locking and unlocking all the messages you'll send and receive in future. This method is called a secret key, because only the two of you will have access to it. The secret key could be something like "Replace every letter in the message with another letter three further on in the alphabet."
So, to send the message "HELLO" to your contact in Rome, you simply move each letter three forward, which gives you "KHOOR." When the person at the other end gets the message, he simply has to move each letter back three positions in the alphabet to find out what you're really saying. In this case, the key isn't a piece of metal you poke in a lock: it's the method of cracking the code by shifting the letters. Real secret keys are obviously much more complex and sophisticated than this.

Flowchart Explaining Encryption

                                       wi-fi Password Encryption (WPA-PSK)
This way of securing information is also called PSK (pre-shared key) and in some circumstances it's very effective. It's widely used to secure wireless Internet networks, for example. When you set up a secure wireless network, you're asked to choose a secret key (effectively, a password) that's known to both your wireless router (your main local access point to the Internet) and to any portable computers that need to use it. When you're using wireless Internet, you may notice that your connection is encrypted with something called WPA-PSK (Wi-Fi Protected Access-Pre-Shared Key). If you try to log onto a new wireless network and you're asked for a password, what you're really supplying is a secret key that will be used to encrypt and decrypt all the messages that pass back and forth.

Although secret (pre-shared) keys are effective and secure for things like this, they're not at all useful in other situations—like sending secure messages to people you've never met. That's because they rely on your knowing and meeting the person you're communicating with in advance to exchange the secret key. What if you can't do that? What if you want to exchange secure information with someone you've never met—someone who could be on the opposite side of the world? That's exactly the problem you have when you're paying for things online.

Public-key Encryption:

In that case, you can use a different system called public-key cryptography, which is how online encryption works. The basic idea is simple.
Each person has two keys, one called a public key and one called a secret key. Each "key" is actually a long, meaningless string of numbers—nothing like a metal key you'd use to open and close a door lock. The public key is something you can share with anyone, while the secret key is something you must keep private. Suppose you want to send a message to a friend using public key cryptography. You use their public key (which they've freely shared with the world) to encrypt the message and turn it into gibberish. You email the scrambled message to them over the Internet and when they receive it they use their secret key to decrypt (unscramble) and read it.

Public-key cryptography: Anyone can encrypt a message and send it to you (using your public key), but only you can read it (using your secret key).

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