Future Business Leaders of America (FBLA) Cybersecurity Practice Test

The Data Encryption Standard (DES) is classified as a symmetric-key cipher because it uses the same key for both the encryption and decryption processes. In symmetric-key cryptography, both the sender and the recipient must possess the same secret key and keep it confidential in order to securely communicate. DES operates through a series of permutations and substitutions on plaintext data using this shared key to produce ciphertext, and the same key is required to revert that ciphertext back into plaintext.

In contrast, asymmetric-key ciphers use a pair of keys—a public key that can be shared widely and a private key that is kept secret. This means that data encrypted with the public key can only be decrypted using the corresponding private key. Since DES does not utilize this two-key system, it does not fit into the classifications of public-key or asymmetric-key encryption.

The term “private-key” tends to be used interchangeably with symmetric-key in some contexts, as both involve the use of a single shared secret key. However, in the more common jargon of cryptography, “symmetric-key” is the preferred term for clarity. Thus, "symmetric-key" is the most precise classification for DES, making it the correct answer.