SSCP Cryptography Practice Question
A security analyst is recommending a symmetric encryption algorithm for a new application that requires both confidentiality and authentication. Which algorithm and mode combination should they select?
⚠ Common exam trap
Many exam-takers confuse CBC mode with providing authentication (since it uses an IV), but CBC only offers confidentiality; GCM is the correct choice for combined confidentiality and authentication in symmetric encryption.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AES-GCM
AES-GCM (Galois/Counter Mode) is a symmetric encryption algorithm that provides both confidentiality and authentication in a single, efficient operation. It combines AES encryption in counter mode with a Galois field-based message authentication code (GMAC), making it ideal for applications requiring both security properties.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
3DES-CBC
Why it's wrong here
CBC supplies confidentiality only; it lacks a message authentication code, so ciphertext modifications go undetected. It is tempting because 3DES-CBC was long the standard for bulk encryption, and would be acceptable where integrity is handled separately, such as an encrypt-then-MAC construction.
- ✗
AES-ECB
Why it's wrong here
ECB mode is not recommended due to pattern leakage and does not provide authentication.
- ✗
RC4
Why it's wrong here
RC4 is a stream cipher with known keystream biases and no integrity mechanism, so it cannot supply authentication. It is tempting for its speed and simplicity in legacy TLS or WEP contexts, but those deployments are deprecated precisely because RC4 fails confidentiality and authenticity guarantees.
- ✓
AES-GCM
Why this is correct
AES-GCM is a block cipher in Galois/Counter Mode, providing authenticated encryption: confidentiality plus an authentication tag verifying integrity and origin. This satisfies the stem's dual requirement for confidentiality and authentication in one symmetric primitive, unlike CBC or CTR, which lack built-in authentication.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SSCP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SSCP exam.