200-201 Security Concepts Practice Question
A security analyst is selecting a symmetric encryption algorithm for encrypting data at rest. Which of the following is a suitable symmetric algorithm?
⚠ Common exam trap
The trap is that candidates see 'SHA-256' and assume it is an encryption algorithm because it sounds cryptographic — but hashing is one-way and cannot encrypt/decrypt data, and asymmetric algorithms like RSA/ECC are often confused with symmetric ones under exam pressure.
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
AES (Advanced Encryption Standard) is a symmetric block cipher, meaning it uses the same key for both encryption and decryption, making it suitable for encrypting data at rest. It is widely adopted, standardized by NIST, and available in 128-, 192-, and 256-bit key lengths. AES is the de facto standard for symmetric encryption in modern systems.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
AES
Why this is correct
AES is the only symmetric block cipher listed, satisfying the data-at-rest requirement. It encrypts and decrypts with one shared key, unlike RSA and ECC, which are asymmetric. AES-256 offers strong resistance to brute-force attacks and is the standard choice for protecting stored data.
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ECC
Why it's wrong here
ECC is an asymmetric key-agreement and signature scheme built on elliptic-curve discrete logarithms, so it cannot perform bulk symmetric encryption of data at rest. It would be the right selection for key exchange, digital signatures or certificate public keys, not for ciphering stored data.
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RSA
Why it's wrong here
RSA is asymmetric, using a public/private key pair, and is far too slow for bulk data-at-rest encryption. It is correctly chosen for key transport, digital signatures or TLS handshake authentication, whereas symmetric ciphers such as AES handle the actual data encryption.
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SHA-256
Why it's wrong here
SHA-256 is a one-way hash producing a fixed 256-bit digest; it has no key and cannot be reversed, so it cannot encrypt data at rest. It is correctly used for integrity verification, password derivation within PBKDF2, or digital signature digests, not confidentiality.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 200-201 practice question is part of Courseiva's free Cisco 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 200-201 exam.