In cryptography, a message authentication code (MAC), sometimes known as an authentication tag, is a short piece of information used for authenticating and integrity-checking a message. In other words, to confirm that the message came from the stated sender (its authenticity) and has not been changed (its integrity). The MAC value allows verifiers (who also possess a secret key) to detect any changes to the message content. Informally, a message authentication code system consists of three algorithms: A key generation algorithm selects a key from the key space uniformly at random. A signing algorithm efficiently returns a tag given the key and the message. A verifying algorithm efficiently verifies the authenticity of the message given the same key and the tag. That is, return accepted when the message and tag are not tampered with or forged, and otherwise return rejected.

A digital signature is the most comprehensive solution as it addresses both file integrity and sender authenticity, making it the best choice for compliance with the requirement.

I think the others verify data integrity but not sender authenticity.

The best option for the MSSP to configure to meet this objective is RSA (Option B). RSA (Rivest-Shamir-Adleman) is an algorithm used by modern computers to encrypt and decrypt messages. It is an asymmetric cryptographic algorithm, meaning it uses two different keys: one public key for encryption and one private key for decryption. This is ideal for secure communications as the public key can be distributed widely while the private key remains secret. RSA is widely used in electronic commerce protocols and is considered secure when used properly. It’s also recognized and accepted by many government standards, making it suitable for a client with government compliance requirements.

The best way for the security team to comply with this requirement is through a Digital Signature (Option A). A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. It provides a layer of validation and security to messages sent through a non-secure channel. Digital signatures can provide evidence of origin, identity and status of an electronic document, transaction or message and can acknowledge informed consent by the signer. In many countries, including the United States, digital signatures are considered legally binding in the same way as traditional document signatures. This makes them an ideal choice for verifying the integrity of a downloaded file and the sender of the file

I agree with A, if the question did not involve the integrity of the sender of the file, and just the integrity of the data I would go with hash.

A. Digital signature. It provides both the needed data integrity and sender authentication using asymmetric cryptography, ensuring compliance with the stated requirement.