Explanation

"A network-based IDS has little negative affect on overall network performance, and because it is deployed on a single-purpose system, it doesn't adversely affect the performance of any other computer." Pg 34 Krutz: CISSP Prep Guide: Gold Edition.

Encryption would be one of your last layer within Defense in Depth. When we
encrypt files, for the most part they are useless to anyone (they can't get access to the plaintext)
except the person possessing the encryption key to decrypt the files.
With strong encryption we can assume that they are safe so long as the encryption key is secured.
This process provides confidentiality that the data has not been divulged, even if captured
(Sniffed) or otherwise stolen while in transit or in storage.
Consider this mnemonic to help you remember the basic cryptographic goals:
P: Privacy (or confidentiality)
A: Authentication
I: Integrity
N: Non-repudiation
The following answers are incorrect:
Authentication: Authentication isn't insured by encryption alone. Incorrect.
Integrity: Encryption doesn't insure integrity. Hashing algorithms would be used instead. Sorry.
Incorrect answer.
Non-repudiation: Sorry, encryption alone doesn't insure non-repudiation. You would need to have
a valid Public Key Infrastructure (PKI) in place along with the proper processes.
The following reference(s) was used to create this question:
Gregg, Michael; Haines, Billy (2012-02-16). CASP: CompTIA Advanced Security Practitioner
Study Guide Authorized Courseware: Exam CAS-001 (p. 3). Wiley. Kindle Edition.