Explain why symmetric-key encryption has a key-management problem, and describe how the lesson’s hybrid approach addresses it.

### Why this is right The challenge is that symmetric encryption needs both parties to possess the same secret, while sending that secret openly could expose it. A hybrid design uses public-key cryptography to protect the symmetric session key and efficient symmetric encryption for the message itself. ### The concept A session key is a temporary symmetric key used for one communications session. The sender encrypts the message with that key, then encrypts the key using the recipient’s public key. The recipient’s corresponding private key recovers the session key, which can then decrypt the message. This combines the efficient data processing of symmetric encryption with a way to protect key delivery. The lesson says the session key is discarded after the message is sent and should not be reused. ### What a good answer covers - The same secret key is used for symmetric encryption and decryption. - The key must reach the other party without being exposed. - The message uses a symmetric session key, while the recipient’s public key protects that key. - The session key is temporary and discarded after the session. ### Terms - **Hybrid encryption**: A design combining symmetric and asymmetric cryptographic methods. - **Session key**: A temporary symmetric key for one communications session. - **Public key**: A key that can be shared openly and is used in the relevant public-key operation. - **Private key**: The corresponding secret key, held by its owner. ### Remember Use public-key methods to protect the session key and symmetric methods to protect the bulk message.