Which statement about symmetric cryptography is true?

• A. It uses public/private key pairs
• B. It is best for digital signatures
• C. It uses the same key for encryption and decryption, suitable for bulk confidentiality
• D. It requires certificates for operation

Answer: (C)

Symmetric cryptography relies on a single shared secret for both encryption and decryption, which makes it fast and well-suited for protecting large amounts of data (bulk confidentiality). Once the shared key is securely exchanged, you can encrypt and decrypt big datasets efficiently using algorithms like AES. The other ideas belong to different approaches: public/private key pairs are fundamental to asymmetric cryptography, which handles key exchange and digital signatures rather than bulk data encryption; digital signatures rely on private keys to create a verifiable signature, something symmetric schemes cannot provide; and certificates are part of PKI to bind public keys to identities, not needed when you only use a shared secret key. So using the same key for both directions and applying it to bulk confidentiality is the correct characterization.