AdvancedTechnical
5 min
KMS and Envelope Encryption Design
SecurityEncryptionCloud
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Interview Question
Explain how you would design application-layer encryption using a cloud KMS and envelope encryption for sensitive data.
Key Points to Cover
- Use KMS to manage CMKs; generate DEKs for data encryption
- Encrypt data with DEK; store encrypted DEK alongside ciphertext
- Rotate CMKs and re-encrypt DEKs (not bulk data) periodically
- Audit key usage and enforce IAM least privilege
- Handle performance with caching and envelope patterns
Evaluation Rubric
Describes envelope encryption pattern correctly35% weight
Explains key rotation and auditing25% weight
Secures KMS access via IAM20% weight
Addresses performance and caching20% weight
Hints
- 💡Separate keys by data domain and environment.
Common Pitfalls to Avoid
- ⚠️**Directly Encrypting Data with CMK:** Misunderstanding envelope encryption and attempting to use the KMS CMK to directly encrypt large amounts of data, leading to performance issues and exceeding KMS operational limits.
- ⚠️**Insufficient DEK Granularity:** Using a single DEK for a very large dataset, making key rotation and management more complex and potentially exposing more data if a single DEK is compromised.
- ⚠️**Ignoring DEK Re-encryption on CMK Rotation:** Failing to re-encrypt the DEKs when the CMK is rotated, leading to orphaned encrypted DEKs and data that can no longer be decrypted.
- ⚠️**Over-reliance on Application-Level Key Management:** Implementing custom, insecure key management logic within the application instead of leveraging the robust, audited KMS services.
- ⚠️**Inadequate Access Control to KMS:** Granting overly permissive access to KMS, allowing unauthorized principals to generate, encrypt, or decrypt DEKs, thereby compromising data security.
Potential Follow-up Questions
- ❓How do you handle multi-region key availability?
- ❓What about client-side vs server-side encryption?
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