mediumMultiple Choice
CISA Practice Question: During a penetration test, a tester discovers…
During a penetration test, a tester discovers that an application stores passwords using a reversible encryption algorithm. Which of the following is the BEST remediation?
⚠ Common exam trap
Many candidates confuse encryption with hashing, thinking that a strong encryption algorithm like AES-256 is sufficient for password storage, when in fact any reversible method is insecure for this purpose.
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
✓
Implement a strong one-way hashing algorithm such as bcrypt
Storing passwords using reversible encryption is fundamentally flawed because any encryption key can be compromised, allowing an attacker to decrypt all passwords. The best remediation is to use a strong, one-way hashing algorithm like bcrypt, which is designed to be computationally expensive and includes a built-in salt to resist rainbow table attacks and brute-force attempts. Unlike encryption, hashing is irreversible, so even if the database is breached, the original passwords cannot be recovered.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use MD5 hashing with a salt
Why it's wrong here
MD5 is a fast, unsalted-by-default hash vulnerable to rainbow tables and GPU cracking; salting does not fix its speed. It is tempting because it removes reversibility, but password storage requires a slow, salted algorithm such as bcrypt, scrypt or Argon2.
- ✗
Replace the encryption algorithm with AES-256
Why it's wrong here
AES-256 remains reversible encryption, so anyone with the key decrypts every stored password. It is tempting because AES-256 is strong and replaces the weak algorithm, but password storage demands a one-way salted hash such as bcrypt, scrypt or Argon2, not symmetric encryption.
- ✓
Implement a strong one-way hashing algorithm such as bcrypt
Why this is correct
Reversible encryption lets anyone with the key recover plaintext passwords, so a breach exposes every credential. One-way hashing with bcrypt, incorporating salting and a tunable work factor, makes recovery computationally infeasible while still verifying logins.
- ✗
Add a random salt before encryption
Why it's wrong here
Salting before encryption still leaves the ciphertext reversible with the key, so an attacker who obtains the key recovers every password. It is tempting because salts defeat precomputation, but that applies to hashing; passwords must be stored with a one-way salted hash.
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 CISA practice question is part of Courseiva's free ISACA 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 CISA exam.