Explain ‘Cryptography’ and the need for keys.

Cryptography is a means to keep data secure and in a form
that can be understood only by someone who has the key to decrypt the data that has been
encrypted.

A key is basically a set of rules which are used
to manipulate the values that form the data which is being worked on to convert them to
a set of random values for someone who does not have access to the key. There are many
forms of encryption techniques which are used. The method used initially required a
private key which was the same for both encrypting as well as decrypting the data. The
key had to be kept in a very secure location and this was a little difficult if the
number of users sending encrypted data back and forth was
large.

A new way of encryption which uses separate keys for
encryption and decryption is in use now. This requires two keys. The key to encrypt the
data is made available to all users who want to send information and is called a public
key. The key to decrypt the encrypted data is called a private key and is required only
by the user who is receiving the data. This makes it necessary to have just one copy of
the private key and makes it easier to keep it secure.