Which type of encryption uses a shared key?

Symmetric encryption utilizes a shared key for both the encryption and decryption processes, making it a fundamental aspect of this encryption type. In symmetric encryption, both the sender and the receiver use the same key, meaning that anyone possessing this key can both encrypt and decrypt the data. This approach is efficient for situations where both parties need quick access to the data, as the same key is employed rather than relying on a complicated relationship between separate keys, as seen in asymmetric encryption.

The primary advantage of symmetric encryption is its speed and efficiency, especially useful when handling large volumes of data. However, it also poses challenges, such as the necessity of securely sharing the key between parties. If the key is intercepted or compromised, the entire system's security can be compromised.

In contrast, asymmetric encryption employs a pair of keys—one public and one private—making it inherently more secure for key exchange but also more resource-intensive. Hashing is a one-way process that converts data into a fixed-size string of characters, while tokenization replaces sensitive data with non-sensitive placeholders, neither of which involves shared keys for encryption and decryption. Therefore, symmetric encryption is the only type from the options given that specifically involves the use of a shared key.