What is a key difference between symmetric and asymmetric cryptography?

• A. Symmetric uses one key for encryption and decryption (e.g., AES); Asymmetric uses a public/private key pair (e.g., RSA) for key exchange and signatures
• B. Symmetric uses two keys for encryption and decryption; Asymmetric uses only one key
• C. Symmetric is slower than asymmetric
• D. Symmetric is only for hashing

Answer: (A)

The key difference is how keys are used to protect data. In symmetric encryption, the same secret key is used to both encrypt and decrypt the message, which makes it fast and suitable for handling large amounts of data. The catch is that this key must be shared securely with anyone who needs to read the data, since both encryption and decryption rely on the same secret key. A good example is AES, a widely used symmetric algorithm.

In asymmetric encryption, you work with a pair of keys: a public key and a private key. The public key can be shared openly and is used to encrypt data or verify a signature, while the private key stays secret and is used to decrypt data or create a signature. This setup solves the key-distribution problem because you don’t have to securely send a secret key to everyone who needs to read the data; you only share the public key.

Because of this difference, the two kinds of systems excel in different roles. Symmetric encryption is normally faster and is great for encrypting large volumes of data, but you need a secure channel or prior arrangement to share the secret key. Asymmetric encryption is slower and more computationally intensive, but it enables secure key exchange and digital signatures without needing a secure key distribution path.

So the best fit here is that symmetric uses one key for both directions, while asymmetric uses a public/private key pair for purposes like key exchange and signatures. The other statements mischaracterize symmetric, suggesting it uses two keys, is slower, or is only for hashing.