What type of encryption uses one key for both encryption and decryption?

Symmetric encryption utilizes a single key for both the encryption and decryption processes. This means that the same key is shared between parties who need to communicate securely, allowing them to encrypt messages before sending them and then decrypt the messages upon receipt using the same key.

The primary advantage of symmetric encryption is its efficiency and speed, making it suitable for encrypting large amounts of data. However, the challenge lies in securely sharing the key, as if the key is intercepted, the security of the communication can be compromised.

In contrast, asymmetric encryption employs two different keys: a public key, which anyone can use to encrypt messages, and a private key, which only the owner has and is used for decryption. Public key encryption is often seen as more secure for key distribution, but it is generally slower than symmetric encryption.

SSL (Secure Sockets Layer) is a protocol that utilizes both symmetric and asymmetric encryption to secure online communications, but it doesn't fit the definition provided by the question as it refers to a method rather than a type of encryption itself.

By focusing on these characteristics, it’s clear that the correct choice for the type of encryption that uses the same key for both encryption and decryption is indeed symmetric encryption.