## Symmetric Key Cryptography

• Symmetric key cryptography also called as Secret key cryptography or Symmetric cipher models.
• Symmetric key cryptography a single key is used for encryption as well as decryption
• Sender encrypts plain text using shared secret key and the resultant cipher text is transmitted through a communication medium such as Internet, at the receiver side, the cipher text is decrypted using the same decryption key to obtain the original plain text.
• Note that encryption and decryption process uses well known symmetric key algorithm called as Data Encryption Standard (DES). • Mathematically it is represented as

### P = D (K, E(P)).

• Where P = Plain Text, E (P) = Encryption of plain text, D (IC, E(P)) = Decryption of Plain text using shared key K.
• For Example Stream and block cipher, Data Encryption Standard (DES), Advance Encryption Standard (AES) and BLOFISH.
• Here the possibility is that if an attacker/opponent got cipher text ?? he/she may apply different permutations and combinations to decrypt and obtain the original plain text. Here the main aim of cryptography comes into the picture. Always sender has to think of applying different encoding technique on plain text message and convert it into ciphertext message so that attacker cannot read the actual plain text easily.

### Advantages of Symmetric key cryptography

• Symmetric key is faster than asymmetric key cryptography.
• Because of single key data cannot decrypt easily at receiver side even if it is intercepted by attacker.
• As the same key is used for encryption and decryption, receiver must have the senders key otherwise he cannot decrypt (without sender permission).
• Symmetric key achieves the authentication principle because it checks receiver’s identity.
• DES and AES techniques are implemented using symmetric key cryptography.
• System resources are less utilized in symmetric key cryptography.

### Disadvantages of Symmetric key cryptography

• Once the key is stolen while transmitting data between sender and receiver it is very easy to decrypt the message as the same key is used for encryption and decryption.
• In symmetric key cryptography, key is transmitted first and then a message is transferred to the receiver. If attacker intercepts the communication between sender and receiver, then he can decrypt the message before it reaches to intended recipients.