selective-encrypted-storage-pattern

# Selective Encrypted Storage Security Pattern Application explicitly encrypts specific sensitive data elements before persisting them to storage. Application controls which data is encrypted and manages encryption operations. ## Problem Addressed **Leak data at rest**: Sensitive data stored in databases, files, or other storage could be accessed by unauthorized parties (database breach, stolen backups, etc.). ## Core Components | Role | Type | Responsibility | |------|------|----------------| | **Application** | Entity | Decides what to encrypt, invokes encryption | | **Cryptographer** | Cryptographic Primitive | Performs encryption/decryption | | **Storage** | Storage | Persists data (encrypted and plaintext) | ### Data Elements - **d**: Plaintext sensitive data - **{d}_k**: Ciphertext - **keyInfo**: Key identification/material - **config**: Cipher configuration ## Pattern Flow ### Storage ``` Application → [encrypt(d, keyInfo, config)] → Cryptographer Cryptographer → [{d}_k] → Application Application → [store({d}_k)] → Storage ``` ### Retrieval ``` Application → [retrieve] → Storage Storage → [{d}_k] → Application Application → [decrypt({d}_k, keyInfo, config)] → Cryptographer Cryptographer → [d] → Application ``` ## Key Characteristics ### Application-Controlled - Application decides WHAT data to encrypt - Application invokes encryption before storage - Application invokes decryption after retrieval ### Field-Level Granularity - Encrypt specific fields (SSN, credit cards, etc.) - Non-sensitive data stored plaintext - Enables partial data access ### Key Per Data Type - Different keys for different sensitivity levels - Key compromise limits exposure - Supports key rotation per data category ## When to Use ### Use Selective Encryption When: - Only specific fields are sensitive - Different data needs different protection levels - Need to query non-sensitive fields - Application must control encryption ### Consider Transparent Encryption When: - All data equally sensitive - Simpler implementation preferred - Database/filesystem encryption sufficient ## Security Considerations ### Key Management Critical - Keys separate from encrypted data - Use Key Management Service (KMS) or HSM - Implement key rotation - Audit key access ### Algorithm Selection - AES-256-GCM (authenticated encryption) - RSA-3072+ for key encryption - Follow Encryption pattern guidelines ### What to Encrypt Typically encrypt: - Personally Identifiable Information (PII) - Payment card data - Health information - Authentication credentials - Cryptographic keys ### Index/Search Challenges Encrypted data cannot be: - Searched directly - Indexed efficiently - Sorted Solutions: - Blind indexes (hash-based) - Searchable encryption (advanced) - Encrypt only display fields, index separately ### Data Flow Analysis Trace plaintext through entire flow: - Application memory - Logs (never log plaintext!) - Caches - Temporary files - Error messages - Backups ### Performance Impact - Encryption/decryption adds latency - Consider caching decrypted values (securely) - Batch operations where possible ## Implementation Approaches ### Application-Level ``` // Before storage encryptedSSN = encrypt(ssn, ssnKey) db.store(record with encryptedSSN) // After retrieval record = db.retrieve() ssn = decrypt(record.encryptedSSN, ssnKey) ``` ### ORM/Framework Integration Many frameworks support field-level encryption: - Django encrypted fields - Hibernate encryption - ActiveRecord attr_encrypted ### Database Features Some databases offer column-level encryption: - SQL Server Always Encrypted - Oracle TDE column encryption - PostgreSQL pgcrypto ## Key Rotation Strategy 1. Generate new key 2. Re-encrypt data with new key (background) 3. Update key reference 4. Deprecate old key 5. Eventually delete old key Consider: - Dual-key period during rotation - Performance impact of mass re-encryption - Backup/restore implications ## Implementation Checklist - [ ] Identified all sensitive data fields - [ ] Using strong algorithm (AES-256-GCM) - [ ] Keys stored separately from data - [ ] Key management system in place - [ ] Key rotation procedure defined - [ ] Plaintext never logged - [ ] Caches secured - [ ] Backup encryption addressed - [ ] Search/index strategy defined - [ ] Performance tested ## Related Patterns - Transparent encrypted storage (alternative: encrypt everything) - Encryption (underlying operations) - Cryptographic key management (key handling) - Selective encrypted transmission (encryption in transit) ## References - Source: https://securitypatterns.distrinet-research.be/patterns/07_01_001__selective_encrypted_storage/ - OWASP Cryptographic Storage Cheat Sheet