For symmetric key encryption between two parties, how many unique encryption keys are necessary?

In symmetric key encryption, both parties involved in the communication use the same encryption key for both encryption and decryption processes. This means that they need a single shared key to secure their communications.

When a sender wants to encrypt a message, they use this key to transform plaintext into ciphertext. The receiver, who possesses the same key, can then reverse this process to decrypt the ciphertext back into plaintext. Since both the sender and receiver operate with the same key for both tasks, only one unique encryption key is required for their entire exchange.

This differs from asymmetric encryption, where two separate keys (a public key and a private key) are utilized, leading to the misconception that more than one key is typically necessary. However, in the context of symmetric key encryption, a single key suffices for the secure transmission of data between the two parties.