What is the main difference between symmetric and asymmetric encryption?

The distinction between symmetric and asymmetric encryption fundamentally lies in the key usage for encryption and decryption processes. In symmetric encryption, the same key is employed for both functions, meaning that the sender and recipient must securely share this key beforehand. This method allows for quicker encryption and decryption since only one key is involved, facilitating faster processing speeds.

On the other hand, asymmetric encryption operates on a different principle, utilizing a pair of keys—one public and one private. The public key can be shared openly to encrypt data, while the corresponding private key is kept secret for decryption. This separation enhances security for key distribution since the private key does not need to be shared and can remain confidential.

While the other options present certain characteristics of these encryption methods, they do not capture the essential difference as effectively as the correct choice. Option A misrepresents symmetric encryption as it uses only one key; option B correctly points out that symmetric is generally faster, but it does not address the key difference; option D inaccurately portrays symmetric encryption as outdated, while in reality, both methods are widely used in different contexts depending on the security requirements.