implementing-envelope-encryption-with-aws-kms

# Implementing Envelope Encryption with AWS KMS ## Overview Envelope encryption is a strategy where data is encrypted with a data encryption key (DEK), and the DEK itself is encrypted with a master key (KEK) managed by AWS KMS. This approach allows encrypting large volumes of data locally while keeping the master key secure in a hardware security module (HSM) managed by AWS. This skill covers implementing envelope encryption using AWS KMS GenerateDataKey API. ## Objectives - Understand the envelope encryption pattern and its advantages - Generate data encryption keys using AWS KMS GenerateDataKey - Encrypt/decrypt data locally using DEKs - Store encrypted DEK alongside ciphertext - Implement key caching to reduce KMS API calls - Handle key rotation with automatic re-encryption - Implement multi-region encryption for disaster recovery ## Key Concepts ### Envelope Encryption Flow 1. Call `kms:GenerateDataKey` to get plaintext DEK + encrypted DEK 2. Use plaintext DEK to encrypt data locally (AES-256-GCM) 3. Store encrypted DEK alongside ciphertext 4. Discard plaintext DEK from memory 5. For decryption: call `kms:Decrypt` on encrypted DEK, then decrypt data ### Advantages Over Direct KMS Encryption | Aspect | Direct KMS | Envelope Encryption | |--------|-----------|-------------------| | Max data size | 4 KB | Unlimited | | Latency | Network round-trip per operation | Local encryption | | Cost | $0.03/10,000 requests | Fewer KMS requests | | Offline | Not possible | Yes (with cached DEKs) | ### KMS Key Types - **AWS Managed**: AWS creates and manages (`aws/s3`, `aws/ebs`) - **Customer Managed**: You create and manage policies - **Custom Key Store**: Backed by CloudHSM cluster ## Security Considerations - Never store plaintext DEK; only keep encrypted DEK - Use key policies to restrict who can call GenerateDataKey and Decrypt - Enable AWS CloudTrail logging for all KMS API calls - Implement key rotation (automatic annual rotation for CMKs) - Use encryption context for authenticated encryption metadata - Handle KMS throttling with exponential backoff ## Validation Criteria - [ ] GenerateDataKey returns plaintext and encrypted DEK - [ ] Data encrypts correctly with plaintext DEK using AES-256-GCM - [ ] Encrypted DEK can be decrypted via KMS Decrypt API - [ ] Decrypted DEK recovers the original data - [ ] Plaintext DEK is wiped from memory after use - [ ] Encryption context is validated during decryption - [ ] Key rotation re-encrypts DEKs with new master key @ref(api-reference.md) @ref(standards.md) @ref(workflows.md)