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:
madhuvrata srngisodadhisandhiga I
Khalajivitakhatava galahalarasandhara II
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
To remember the value of pi upto 31 decimal places
cryptography techniques were used by Ancient India.
CAESAR CREATED A SECURE CIPHER! (Ancient Crptography)
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.
Alphabet: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Caesar Alphabet: X Y Z A B C D E F G H I J K L M N O P Q R S T U V W
EXAMPLE:The messageTHE ENEMY IS
be written QEB
BKBJV FP KBXOusing
the Caesar Cipher system.
As theInternet and other forms of electronic communication become
more prevalent, electronicsecurityis
becoming increasingly important. Cryptography is used to protecte-mailmessages, credit card information, and
In modern days cryptography has become securing information
from an eve. More generally, cryptography is about constructing and analyzingprotocolsthat block Eve (or adversaries);various
securitysuch as dataconfidentiality,data integrity,authentication, andnon-repudiationare central to modern cryptography.
Modern cryptography exists at the intersection of the disciplines ofmathematics,computer science, andelectrical 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
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
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.
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
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.
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.
In that case, you can use a different system called
public-key cryptography, which is how online encryption works. The basic idea
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).