Initial commit - 611 cybersecurity skills across all subdomains

skills/implementing-envelope-encryption-with-aws-kms/SKILL.md

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+---
+name: implementing-envelope-encryption-with-aws-kms
+description: 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 
+domain: cybersecurity
+subdomain: cryptography
+tags: [cryptography, encryption, aws, kms, envelope-encryption, key-management]
+version: "1.0"
+author: mahipal
+license: MIT
+---
+# 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