What are the two types of symmetric encryption?

The correct choice identifies the two types of symmetric encryption as block and stream ciphers.

Block ciphers operate on fixed-size blocks of plaintext, typically encrypting data in chunks (such as 128 bits or 256 bits), ensuring the same block of plaintext will always produce the same ciphertext when encrypted with the same key. This makes block ciphers suitable for encrypting data that can be divided into these fixed-sized segments. Examples of block ciphers include AES (Advanced Encryption Standard) and DES (Data Encryption Standard).

On the other hand, stream ciphers encrypt data one bit or byte at a time, allowing for a more flexible encryption process that can be suited for applications where data is continuously flowing, such as streaming audio or video. Stream ciphers generate a keystream that is then XORed with the plaintext, providing a similar level of security as block ciphers but often with increased performance in certain scenarios. Examples include RC4 and Salsa20.

Both cryptographic methods are fundamental to symmetric encryption, highlighting their importance in securing data.