The answer is to configure an S3 bucket policy that grants the third-party account access to the objects and update the KMS key policy to allow the third-party account to decrypt using the key. This two-step process is required because cross-account S3 KMS sharing demands permissions at both the resource level and the key level: the bucket policy authorizes the third party to list and retrieve objects, while the KMS key policy must explicitly grant the decrypt permission to the external account’s root user or IAM roles. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of the layered security model where S3 bucket policies handle resource access and KMS key policies control cryptographic operations, a common trap being that granting bucket access alone fails silently if the key policy is missing. A useful memory tip is “bucket for objects, key for decrypt”—always check both policies when sharing encrypted data across accounts.
DEA-C01 Data Security and Governance Practice Question
This DEA-C01 practice question tests your understanding of data security and governance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 financial services company needs to share sensitive customer data with a third-party analytics firm. The data resides in an S3 bucket encrypted with an AWS KMS customer managed key. The third party has their own AWS account. Which combination of steps is required to securely share the data? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Update the KMS key policy to include the third-party account as a principal with kms:Decrypt permission
Options A and D are correct. Option A: The S3 bucket policy must grant cross-account access. Option D: The KMS key policy must grant decrypt permission to the third-party account. Option B is wrong because the third party does not need access to the KMS key management. Option C is wrong because the third party should not have cross-account access to the S3 bucket without appropriate permissions. Option E is wrong because sharing the KMS key directly is not secure.
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.
✗
Share the KMS key material with the third party
Why it's wrong here
Sharing key material is insecure and not recommended.
✓
Update the KMS key policy to include the third-party account as a principal with kms:Decrypt permission
Why this is correct
The key policy must allow the third party to decrypt.
Related concept
Static NAT maps one inside address to one outside address.
✗
Create an IAM role in the third-party account that can be assumed by the data owner
Why it's wrong here
The third party should assume a role in the data owner account, not the other way.
✗
Grant the third-party account access to the KMS key management
Why it's wrong here
They only need decrypt permission, not management.
✓
Configure an S3 bucket policy that grants the third-party account access to the objects
Why this is correct
The bucket policy must allow the third-party account to read objects.
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 DEA-C01 NAT questions on configuration and troubleshooting.
Data Security and Governance — This question tests Data Security and Governance — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Update the KMS key policy to include the third-party account as a principal with kms:Decrypt permission — Options A and D are correct. Option A: The S3 bucket policy must grant cross-account access. Option D: The KMS key policy must grant decrypt permission to the third-party account. Option B is wrong because the third party does not need access to the KMS key management. Option C is wrong because the third party should not have cross-account access to the S3 bucket without appropriate permissions. Option E is wrong because sharing the KMS key directly is not secure.
What should I do if I get this DEA-C01 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 DEA-C01 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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