Final answer:
HMAC is the correct choice for a message authentication code used to verify the legitimacy of a file or message, as it includes a cryptographic hash and a secret key for enhanced security.
Step-by-step explanation:
The correct answer to the question is c) HMAC, which stands for Hash-based Message Authentication Code. A HMAC is used to verify the integrity and authenticity of a message or file, ensuring that it has not been tampered with. It combines a cryptographic hash function like SHA or MD5 with a secret cryptographic key.
Other options like RIPEMD, MD5, and SHA are cryptographic hash functions that can provide a unique fingerprint for a set of data, but without a key, they cannot be used for message authentication in the same way as HMAC. An HMAC includes both the hash of the message and a secret key, providing a stronger guarantee that the message originated from a particular sender and has remained unaltered.