Which class of cryptography involves algorithms like AES and DES?

The correct answer identifies a class of cryptography characterized by the processing of data in fixed-size blocks. Algorithms such as AES (Advanced Encryption Standard) and DES (Data Encryption Standard) are prime examples of block cipher algorithms. In block cryptography, the plaintext is divided into blocks of a specific size (e.g., 128 bits for AES) and each block is encrypted individually, producing a corresponding block of ciphertext.

This method allows for secure and efficient data encryption since the same key is used for encrypting multiple blocks, facilitating both security and speed in data processing. Block ciphers have standard modes of operation that control how multiple blocks interact, such as CBC (Cipher Block Chaining) and CTR (Counter Mode), which extends their functionality in various applications.

By contrast, asymmetric cryptography uses key pairs (public and private keys) and is used primarily for secure key exchange and digital signatures. Synchronous and stream cryptography typically deal with data elements one bit or byte at a time instead of fixed blocks, which distinguishes them from the block methods employed by AES and DES.