Ablock cipher:

A.
Converts a variable-length of plaintext into a fixed length ciphertext.

B.
Is an asymmetric key algorithm.

C.
Encrypts by operating on a continuous data stream.

D.
Breaks a message into fixed length units for encryption.

Explanation:
The correct answer is “Breaks a message into fixed length units for encryption”. Answer “Encrypts by
operating on a continuous data stream” describes a stream cipher. Answer “Is an asymmetric key
algorithm” is incorrect because a block cipher applies to symmetric key algorithms; and answer
“Converts a variable-length of plaintext into a fixed length ciphertext” describes a hashing operation.