You want to ensure that a user that sent an email cannot later claim that he did not send it. What should be used?
D. Access control
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Answer: C. Non-repudiation can be used to prevent someone from later denying an action. Non-repudiation is commonly enforced with digital signatures. Confidentiality is used to prevent the unauthorized disclosure of information, often by encrypting the data. Integrity is used to verify that data has not been modified and is enforced with hashing or message authentication codes. Access control is one of many methods used to grant access to entities to resources after they have been authenticated.