What is Symmetric Key Encryption?

Symmetric key encryption is a type of encryption in which the same cryptographic key is used for both encryption and decryption. The requirement for this encryption method is that both parties need to have access to the cryptographic key using which the data is encrypted and decrypted. And the secret cryptographic key is called the symmetric key.

How does Symmetric Encryption work?

There are basically two types of symmetric key encryption:

• Stream Ciphers
• Block Ciphers

What are Stream Ciphers?

Stream ciphers encrypt the digits of a message one at a time. Usually, when the message or plaintext comes in quantities of unknowable length, like in the case of a secured wireless connection, a stream cipher is used.

In a stream cipher, each digit of the plaintext is encrypted one at a time, with some corresponding digit of the keystream. After each digit, the state of the keystream changes, and the next digit of the plaintext gets encrypted. Usually, the initial value of the keystream or seed is kept in a shift register, and after each digit of encryption, the state of the shift register changes. Hence, this cipher is also called a state cipher.

Usually, in each state, one bit of the plaintext gets encrypted, and the operation that is performed with the corresponding bit of the keystream is XOR. In each state, the value of the keystream changes using a Linear Feedback Shift Register or LFSR. If the value of the keystream is independent of the plaintext or ciphertext, the stream cipher is called a synchronous stream cipher. And if the previous digits of the ciphertext are used to compute the next value of the keystream, it is called self-synchronizing stream cipher or asynchronous stream cipher.

Because of their speed and simplicity of implementation in hardware, stream ciphers are often used. RC4, A5/1, A5/2, FISH, Helix, ISAAC,, etc are a few stream ciphers that are commonly used in many software.

What are Block Ciphers?

In block cipher, on the other hand, the symmetric key operates on some fixed number of bits of the message or plaintext and creates the ciphertext. The fixed number of bits of data is called a block. The size of …