Cryptography can be broadly defined into two types.

I. Symmetric Key Cryptography

II. Asymmetric Key Cryptography

Symmetric Key cryptography

Symmetric key cryptography is also known as Private key cryptography or secret key cryptography

In symmetric key cryptography a single key is used for both encryption as well as decryption.

Following figure depicts the symmetric key cryptography:

It is represented as P=D(K,E(P))

Where K=Encryption and decryption key

P=Plain text

D=Decryption

E(P)=Encryption of plain text

Advantages of Private key cryptography:

a. It is faster than asymmetric key cryptography.

b. Symmetric key achieves the authentication principle, because receivers identity is checked here

c. As a common key is used for both encryption and decryption, the receiver must have the sender’s key in order to decrypt the message.

d. AES and DES techniques are implemented using symmetric key cryptography

Disadvantages of Private key cryptography:

a. If the common key is stolen, then the data can be easily decrypted as same key is used for both encryption and decryption

b. In private key cryptography, the key is transmitted first and later the message is transmitted. If the attacker intercepts the initial communication between the sender and the receiver, he can intercept and decrypt the message before it reaches the intended receiver

Asymmetric key cryptography

Asymmetric key cryptography is also called as public key cryptography or conventional cryptographic system.

In asymmetric key cryptography two keys are used, our encryption and other is for decryption as shown in Fig.

It is represented as: P=D(Kd,E(Ke,P))

Where Ke=Encryption key

Kd=Decryption key

D=Decryption

E(Ke,P)=Encryption of plain text using encryption key

P=Plain text

For Example: RSA Algorithm and Diffie Hellman key exchange algorithm.

Advantages of Asymmetric key cryptography :

a. In Asymmetric key cryptography key cannot be distributed among sender and receiver as both have their own key so there is no problem of key distribution while transmitting the data over insecure channel.

b. The main advantage of asymmetric key cryptography is that two separate keys are used for encryption and decryption; even if encryption key is stolen by the attacker he/ she cannot decrypt the message as decryption key is only available with the receiver.

c. RSA algorithm and Diffie Hellman key exchange are implemented using asymmetric key cryptography.

Disadvantages of Asymmetric key cryptography :

a. Because of different key used between sender and receiver more time is required to get the transmission done as compared to symmetric key cryptography

b. Asymmetric key cryptography utilizes more resources as compared to symmetric Key cryptography.