Types Of Cryptography

There are two types of Cryptographies.

   a.   Secret key cryptography

   b.   Public key cryptography

Secret key cryptography

It is also known as symmetric key encryption. Let’s say ‘A’ wants to send message to ‘B’, then ‘A’ shares a key with ‘B’ (Assuming that key is not disclosed to any one). Once the key shared between ‘A’ and ‘B’, ‘A’ encrypts the data and send to ‘B’.  Once ‘B’ receives encrypted data, it uses same key to decrypt. Since same key is used for both encryption and decryption, it is called Symmetric Encryption. The larger the key, the more difficult to break the encrypted message.

Public Key Cryptography

The problem with secret key cryptography is in, transferring the key securely between the parties involved in communication. This problem solved by using public key cryptography, also called Asymmetric cryptography. In public key cryptography, encryption is done with public key and decryption is done with private key. Steps are like following.

a.   Person ‘A’, creates public-private key pair.

b.   ‘A’ distribute (publish) his public key, to all the parties involved in communication.

c.    ‘B’ who wants to send information to ‘A’, encrypt the message with ‘A’ ‘s public key and send.

d.   ‘A’ receives the encrypted message, decrypt it with his private key.

Since private key is known to ‘A’ only, it is nearly impossible for any other person to decrypt the message. This seems to be some what magic to, who are new to cryptography.  For complete understanding, go through following wiki article.

http://en.wikipedia.org/wiki/Public-key_cryptography

By using public key encryption, we can provide authentication service also. Let’s say ‘A’ encrypt some info ‘x’ with his private key and send it to ‘B’. Once ‘B’ receives the encrypted message, he decrypts the message with ‘A’ public key and make sure that it is ‘x”. If is there any mismatch in decrypted information, then ‘B’ confirm that it is not ‘A’. Only the problem with public key cryptography is, it is costly, complex mathematical operations performed while encrypting.

So better solution is to combine both Symmetric and Asymmetric algorithms. The main problem with symmetric encryption is, how can key exchange happen securely between ‘A’ and ‘B’.

a.   ‘A’ generates his public-private key pair

b.   ‘A’ sends his public key to ‘B’

c.    ‘B’ generate a random number, and encrypt the random number with ‘A’ public key and send the encrypted message to ‘A’.

d.   ‘A’ receives the encrypted message and decrypts the message with his private key.

e.   At this point of time, both ‘A’ and ‘B’ knows the random number, they use this random number as secret key and perform secret key encryption with this key.

In summary, public key encryption is used for key exchange, secret key encryption is used for data exchange.

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