Which statement is true about symmetric encryption?

• A. Asymmetric encryption uses the same key for encryption and decryption; AES is an example.
• B. Symmetric uses the same key for encryption and decryption; AES is an example; used for bulk data.
• C. Symmetric algorithms cannot be used for authentication.
• D. Asymmetric keys are never used for key exchange.

Answer: (B)

Symmetric encryption uses the same key to both encrypt and decrypt, which makes it fast and efficient for handling large amounts of data. AES is a widely used symmetric algorithm, so it serves as a clear example. This approach is favored for bulk data because it requires less computational effort than asymmetric methods, allowing quick encryption and decryption of big files or streams.

Key distribution is important with symmetric systems, since anyone who has the key can decrypt the data. While symmetric encryption itself focuses on confidentiality and speed, authentication can still be provided when combined with a message authentication code (MAC) that uses the same secret key.

The other statements don’t fit because asymmetric encryption uses a pair of keys (public and private) and is not the same key for encryption and decryption, AES is not an asymmetric algorithm, and symmetric approaches can contribute to authentication through MACs. Also, asymmetric keys are indeed used for key exchange in many protocols to establish a secure channel before using symmetric keys.