Which of the following concepts defines the requirement for data availability?

A.
Authentication to RADIUS

B.
Non-repudiation of email messages

C.
Disaster recovery planning

D.
Encryption of email messages

Explanation:
A disaster-recovery plan, or scheme, helps an organization respond effectively when a disaster occurs. Disasters may include system failure, network failure,
infrastructure failure, and natural disaster. The primary emphasis of such a plan is reestablishing services and minimizing losses.
Incorrect Answers:
A: Authentication issues deals with authorized access to resources.
B: Nonrepudiation prevents one party from denying actions that they carried out and in the electronic world nonrepudiation measures can be a two-key
cryptographic system and the involvement of a third party to verify the validity. This respected third party `vouches’ for the individuals in the two-key system.
D: Encryption of email messages is concerned with confidentiality.

Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, Sixth Edition, Sybex, Indianapolis, 2014, pp 29, 262, 433-434