The correct answer is that the role can decrypt objects in S3, but cannot use the key outside of S3. This is because the KMS key policy uses the kms:ViaService condition, which restricts all key usage to requests that originate specifically from the S3 service in us-east-1. When the application on EC2 calls S3 GetObject with SSE-KMS, the request is made via S3, so the condition is satisfied and decryption succeeds; however, any direct call to KMS (e.g., kms:Decrypt from the EC2 instance itself) would fail because it does not come through S3. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of how kms:ViaService acts as a service-level boundary, a common trap being that candidates assume the role needs explicit kms:Encrypt, when in fact S3 uses GenerateDataKey for encryption. Remember the memory tip: “ViaService ties the key to the service, not the role—S3 is the door, not the user.”
SCS-C02 Data Protection Practice Question
This SCS-C02 practice question tests your understanding of data protection. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Refer to the exhibit. A security engineer configures the above KMS key policy. The DataAccess role is used by an application that runs on EC2 instances in the us-east-1 region. The application needs to read encrypted objects from an S3 bucket in the same region. Which of the following is true about this configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The role can decrypt objects in S3, but cannot use the key outside of S3.
Option A is correct. The condition 'kms:ViaService' restricts the use of the key to requests that originate from S3 in us-east-1. This means the role can only use the key when the request comes through S3 (e.g., S3 GetObject with SSE-KMS). Option B is wrong because the role can still encrypt data via S3 PutObject (GenerateDataKey). Option C is wrong because the condition allows usage via S3. Option D is wrong because the role does not have kms:Encrypt but has kms:GenerateDataKey, which is sufficient for S3 PutObject.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 role can use the key for any S3 operation in any region.
Why it's wrong here
The condition restricts to us-east-1.
✗
The role cannot use the key for any operation because the condition is invalid.
Why it's wrong here
The condition is valid.
✗
The role can only encrypt data, not decrypt it.
Why it's wrong here
The policy allows both Decrypt and GenerateDataKey.
✓
The role can decrypt objects in S3, but cannot use the key outside of S3.
Why this is correct
The condition restricts use to S3 service in us-east-1.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
Data Protection — This question tests Data Protection — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The role can decrypt objects in S3, but cannot use the key outside of S3. — Option A is correct. The condition 'kms:ViaService' restricts the use of the key to requests that originate from S3 in us-east-1. This means the role can only use the key when the request comes through S3 (e.g., S3 GetObject with SSE-KMS). Option B is wrong because the role can still encrypt data via S3 PutObject (GenerateDataKey). Option C is wrong because the condition allows usage via S3. Option D is wrong because the role does not have kms:Encrypt but has kms:GenerateDataKey, which is sufficient for S3 PutObject.
What should I do if I get this SCS-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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