What do symmetric keys rely on for encryption?

Symmetric keys rely on a shared secret for encryption, meaning that the same key is used for both the encryption and decryption processes. This implies that both the sender and the receiver must possess the same key and keep it confidential to ensure the security of the data being exchanged. The security of symmetric encryption allows for fast and efficient processing, making it suitable for encrypting large amounts of data.

In contrast, other options involve different mechanisms. A public/private key pair refers to asymmetric encryption, where different keys are used for encryption and decryption. The Diffie-Hellman exchange is a method for securely exchanging keys over a public channel but does not itself provide encryption. Hash functions are used for verifying data integrity and are not suited for encryption purposes, as they are one-way functions and do not have a reversible process for decryption. Thus, the focus on a shared secret clearly defines the operation of symmetric key encryption.