200-201 Security Concepts Practice Question
Which encryption method uses a single key for both encryption and decryption of data?
⚠ Common exam trap
Cisco often tests the distinction between symmetric and asymmetric encryption by presenting a scenario where a single key is used, and candidates may confuse 'single key' with the public key in asymmetric encryption, leading them to incorrectly select asymmetric 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
✓
Symmetric encryption
Symmetric encryption uses a single shared key for both encryption and decryption of data. This is the defining characteristic of symmetric algorithms like AES, DES, and 3DES, where the same secret key must be known to both sender and receiver to protect confidentiality.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Asymmetric encryption
Why it's wrong here
Asymmetric encryption uses a mathematically related key pair, with the public key encrypting and the private key decrypting, so one key never performs both operations. It is tempting because it underpins TLS and key exchange, and would be correct if the question asked which method avoids sharing a secret key.
- ✓
Symmetric encryption
Why this is correct
Symmetric encryption satisfies the single-key constraint by using one shared secret for both encryption and decryption, as with AES. This contrasts with asymmetric algorithms such as RSA, which employ a public key to encrypt and a mathematically related private key to decrypt, requiring two distinct keys.
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Digital signature
Why it's wrong here
A digital signature applies a private key to a hash for authenticity and integrity; it is not an encryption method and does not decrypt data. It is tempting because it also uses asymmetric cryptography, and would be correct if the question asked how to verify sender identity and message integrity.
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Hashing
Why it's wrong here
Hashing is a one-way transformation producing a fixed-length digest; it is irreversible and uses no key, so it cannot decrypt anything. It is tempting because it protects data integrity and is often grouped with encryption, and would be correct if the question asked how to verify that data has not changed.
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 |
About these practice questions
Courseiva writes every 200-201 question from scratch — 968 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.