CAS-004 Security Architecture Practice Question
During an API security review, an assessor finds that the API uses JSON Web Tokens (JWT) with a symmetric key shared among multiple services. Which of the following is the MOST significant security concern?
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
✓
Multiple services share the same symmetric key
Using a shared symmetric key means any service with the key can forge tokens, compromising authentication integrity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The token is not encrypted
Why it's wrong here
JWT payload is base64-encoded, not encrypted, but that is intended; the shared key is the bigger risk.
- ✓
Multiple services share the same symmetric key
Why this is correct
Shared symmetric keys increase the attack surface and risk of token forgery.
- ✗
The token does not include audience claim
Why it's wrong here
Missing audience claim is a concern but less critical than shared keys.
- ✗
Token expiration is not set
Why it's wrong here
While expiration is important, the shared key issue is more severe.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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