What describes symmetric key encryption?

Symmetric key encryption is defined by the use of the same key for both the encryption and decryption processes. This means that the sender and the receiver both need to possess this secret key to securely share and access the information. The primary advantage of symmetric key encryption is its efficiency in processing speed, making it suitable for encrypting large amounts of data.

In symmetric encryption, since there is only one key, it requires a secure method for key exchange between parties to prevent unauthorized access. This is a fundamental characteristic that distinguishes symmetric key encryption from asymmetric encryption, where different keys are used for these processes.

The other options describe different concepts. Using different keys for encryption and decryption refers to asymmetric encryption, where a pair of keys (public and private) is utilized. Asymmetric key pairs and public key infrastructure are part of a different cryptographic model aimed at providing security through key exchange and identification, which does not apply to symmetric key encryption.