Which of the following best describes symmetric encryption?

Symmetric encryption is characterized by the use of a single key for both the encryption and decryption processes. This means that the same secret key is shared between the parties involved, allowing them to encrypt the data before sending it and then decrypt it upon receipt. The efficiency and simplicity of symmetric encryption make it suitable for scenarios where both the sender and receiver can securely exchange and store the shared key.

The other options presented do not accurately describe symmetric encryption. For example, requiring multiple user permissions to decrypt data is more aligned with access control and user authentication rather than the core principle of symmetric encryption. Similarly, asymmetric key pairs refer to a different method of encryption that uses a public key for encryption and a private key for decryption, which is not applicable to symmetric encryption. Lastly, while symmetric encryption can play a role in user authentication as part of a broader security protocol, it is not primarily used for that purpose.