Which of the following uses the same key to decrypt as it does to encrypt?

Asymmetric encryption uses a mathematically linked key pair - a public key to encrypt and a private key to decrypt - meaning the encrypt and decrypt keys are always different.

Dynamic encryption is not a standard cryptographic classification and does not describe a real encryption paradigm based on key usage.

Certificate-based encryption relies on asymmetric PKI infrastructure, where the certificate's public key encrypts and the holder's private key decrypts.

In symmetric encryption, the same key is used by both the sender to encrypt plaintext and the recipient to decrypt ciphertext. Algorithms such as AES, DES, and 3DES are symmetric - any party who holds the key can both encrypt and decrypt. This property makes key distribution the primary security challenge of symmetric systems.