Explanation:
The calculation of a hash, or digest, of the data that are transmitted and its encryption require the public key of the client (receiver) and is called a signature of the message, or digital signature.
The receiver performs the same process and then compares the received hash, once it has been decrypted with their private key, to the hash that is calculated with the received data. If they are the same, the conclusion would be that there is integrity in the data that have arrived and the origin is authenticated. The concept of encrypting the hash with the private key of the originator provides non repudiation, as it can only be decrypted with their public key and, as the CD suggests, the private key would not be known to the recipient. Simply put, in a key-pair situation, anything that can be decrypted by a sender’s public key must have been encrypted with their private key, so they must have been the sender, i.e., non-repudiation. Choice C is incorrect because, if this were the case, the hash could not be decrypted by the recipient, so the benefit of non-repudiation would be lost and there could be no verification that the message had not been intercepted and amended. A digital signature is created by encrypting with a private key. A person creating the signature uses their own private key, otherwise everyone would be able to create a signature with any public key. Therefore, the signature of the client is created with the client’s private key, and this can be verified—by the enterprise—using the client’s public key. Choice B is the correct answer because, in this case, the customer uses their private key to sign the hash data.