AdvancedSystem-Design
45 min
Design a Secrets Management & KMS Service
SecurityCryptographyComplianceAPIs
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Interview Question
Design a system for storing secrets and managing encryption keys with rotation, auditing, and fine-grained access control.
Key Points to Cover
- Threat model; HSM-backed root of trust and envelope encryption
- Secret storage with ACLs, leasing, dynamic creds, and rotation
- Key management: generation, rotation, revocation, versioning
- Audit logs, tamper-evidence, and break-glass procedures
- Multi-region replication with integrity guarantees
- Client SDKs/agents, caching, and sidecar delivery patterns
Evaluation Rubric
Strong root of trust & crypto model30% weight
Secret/key lifecycle & rotation25% weight
Auditability & governance25% weight
Safe/low-latency secret delivery20% weight
Hints
- 💡Envelope encryption reduces exposure of master keys.
Common Pitfalls to Avoid
- ⚠️Storing secrets directly in code or configuration files without proper encryption.
- ⚠️Lack of a robust root of trust, leading to master keys being vulnerable.
- ⚠️Insufficient auditing, making it impossible to track access or detect misuse.
- ⚠️Overly broad access control policies, granting unnecessary permissions.
- ⚠️Ignoring key rotation and revocation, leading to stale or compromised credentials.
Potential Follow-up Questions
- ❓How do you handle tenant-isolated keys?
- ❓What’s your procedure for key compromise?
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