DES is a block cipher.

• A. Stream cipher
• B. Block cipher
• C. Hash function
• D. Asymmetric cipher

Answer: (B)

DES is a block cipher because it processes data in fixed-size chunks, specifically 64-bit blocks, transforming each block into a corresponding 64-bit ciphertext using a symmetric key. This block-based approach is a hallmark of block ciphers, which contrasts with stream ciphers that operate on a stream of bits or bytes by generating a keystream and XOR-ing it with the plaintext. DES uses a Feistel network with multiple rounds and a 56-bit key to derive round keys, applying the same key to encrypt and decrypt, which is characteristic of symmetric ciphers. It is not a hash function, which would produce a fixed-length digest from input data and be non-reversible, nor an asymmetric cipher, which relies on public/private key pairs for encryption and decryption.