Encryption is the most feasible option for safeguarding data from theft or protecting privacy. It converts sensitive data to something that can be read only by authorized people. Nowadays, there are many encryption solutions available, and we have many options when encrypting our data. Some use symmetric key encryption, and some use public key encryption. But what are symmetric key encryption and public-key encryption? How do they work, and how are they different from each other? In this article, we will discuss that.

What is encryption?

Encryption is a process that takes a plaintext message as input and converts it into an encoded message called ciphertext, such that only authorized people can read it. Decryption is the opposite process. It takes a ciphertext message as input and converts it back into the original plaintext message. These encryption and decryption processes use secret keys to perform their actions. The secret key used in the encryption process is called an encryption key, and the secret key used in the decryption process is called the decryption key.

What is symmetric key encryption?

As said above, encryption and decryption processes use an encryption key and decryption key, respectively, to encrypt or decrypt data. Symmetric key encryption is an encryption process in which the same secret key is used during both encryption and decryption. We call the secret key symmetric key. So, if we encrypt a file using symmetric key encryption using a secret key, we will have to use the same secret key at the time of decryption.

This symmetric key encryption can use either stream ciphers or block ciphers.

What are stream ciphers?

In stream ciphers, each plaintext digit is taken one by one from the plaintext message and encrypted using a keystream. A keystream is basically a stream of pseudo-random characters used as keys. At the time of encryption, each plaintext digit is taken one by one and is encrypted with the corresponding digit of the keystream.

This stream cipher can be of two types:

• Synchronous Stream Cipher
• Asynchronous Stream Cipher

In a synchronous stream cipher, the keystream does not depend on the plaintext or the ciphertext message. It is generated independently. In the case of synchronous stream ciphers, the sender and the receiver of the encrypted message must be in the same step for the decryption to be successful. If a digit is added or removed at the time of transmission, the synchronization will be lost. In practical implementation, various methods are used to restore the synchronization if it gets lost.

In an asynchronous stream cipher, N number of previous ciphertext digits are used to compute the keystream. This Number can vary with the implementation. The receiver of the ciphertext message can automatically synchronize with the keystream generator after receiving N ciphertext digits, which makes it easier to recover if digits are added or lost at the time of transmission.

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 ciphers, the input plaintext message is divided into blocks of a fixed length, and each block is then encrypted with a symmetric key.

If a message produces the same ciphertext message each time it is encrypted with a symmetric key, then the encryption process is supposed to be weak. Because in that case, the attacker can observe the bit patterns in the ciphertext message and guess the plaintext message. So, an Initialization Vector is often used for that purpose. An Initialization Vector is basically a pseudorandom value …