Which cryptographic concept uses the same key for encryption and decryption?

• A. Symmetric Cryptography
• B. Asymmetric Cryptography
• C. Public Key
• D. Private Key

Answer: (A)

Using the same key for both encryption and decryption is the hallmark of symmetric cryptography. In this approach, a single shared secret key converts plaintext to ciphertext and back again. Because both directions rely on the same secret, keeping that key confidential is essential; if it leaks, anyone can read or alter messages. Symmetric algorithms are typically fast and well-suited for encrypting large amounts of data, with common examples like AES and DES.

By contrast, asymmetric cryptography uses a pair of keys: a public key for encryption and a private key for decryption. The public key can be shared openly, while the private key stays secret with the recipient. The terms public key and private key describe the two parts of that pair, not the single-key approach used in symmetric systems.