- A
Use automatic rotation and disable previous key versions after 30 days.
Why wrong: Disabling previous versions would make old data undecryptable.
- B
Use automatic rotation and keep one previous key version indefinitely.
This ensures old data remains decryptable and minimizes versions.
- C
Use manual rotation and delete old key versions after confirmation that all data has been re-encrypted.
Why wrong: Manual re-encryption is required, which contradicts the requirement of no manual re-encryption.
- D
Use symmetric key with purpose SYMMETRIC_ENCRYPT_DECRYPT and set rotation period to 0 (never).
Why wrong: No rotation does not meet the key rotation requirement.
Question 329 of 1,000
hardMultiple ChoiceObjective-mapped
Cloud KMS Key Rotation: Ensuring Decryptability of Old Data
This PCSE practice question tests your understanding of pcse exam topics. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security team has a Cloud KMS key used for encrypting Cloud Storage objects. They need to ensure that when the key is rotated, old data remains decryptable without manual re-encryption. They also want to minimize the number of key versions. Which approach should they take?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Quick Answer
The answer is to use automatic rotation and keep one previous key version indefinitely. This approach is correct because Cloud KMS key rotation best practices ensure that when a new key version is generated for encrypting new data, the previous version remains available for decryption, preserving access to old Cloud Storage objects without any manual re-encryption. By retaining only one previous key version, you minimize the number of key versions while still guaranteeing decryptability of old data. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of Cloud KMS version management and the trade-off between security hygiene and operational simplicity—a common trap is assuming you must re-encrypt old data or disable old versions. Remember the memory tip: “One back, never lack”—keep one prior version to avoid decryptability cracks.
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
✓
Use automatic rotation and keep one previous key version indefinitely.
Option B is correct because Cloud KMS supports automatic key rotation while retaining previous key versions indefinitely. When a key is rotated, new data is encrypted with the latest version, but old data remains decryptable using the previous key version that is kept. This satisfies the requirement of minimizing manual intervention and key version count, as only one previous version is retained.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 automatic rotation and disable previous key versions after 30 days.
Why it's wrong here
Disabling previous versions would make old data undecryptable.
- ✓
Use automatic rotation and keep one previous key version indefinitely.
Why this is correct
This ensures old data remains decryptable and minimizes versions.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use manual rotation and delete old key versions after confirmation that all data has been re-encrypted.
Why it's wrong here
Manual re-encryption is required, which contradicts the requirement of no manual re-encryption.
- ✗
Use symmetric key with purpose SYMMETRIC_ENCRYPT_DECRYPT and set rotation period to 0 (never).
Why it's wrong here
No rotation does not meet the key rotation requirement.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that disabling or deleting old key versions is necessary for security, but the correct approach is to retain previous versions to ensure old data remains decryptable without manual re-encryption.
Detailed technical explanation
How to think about this question
Cloud KMS uses a key ring to manage multiple key versions, each with a unique version ID. When automatic rotation is enabled, a new key version is created at the specified interval (e.g., every 90 days), and the previous version is retained as the primary for decryption. The key material is stored in a hierarchical key management system (HKM) that supports envelope encryption, where data encryption keys (DEKs) are encrypted with the key encryption key (KEK). Retaining one previous version ensures backward compatibility without excessive storage overhead.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this PCSE question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: Use automatic rotation and keep one previous key version indefinitely. — Option B is correct because Cloud KMS supports automatic key rotation while retaining previous key versions indefinitely. When a key is rotated, new data is encrypted with the latest version, but old data remains decryptable using the previous key version that is kept. This satisfies the requirement of minimizing manual intervention and key version count, as only one previous version is retained.
What should I do if I get this PCSE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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