normogen/thoughts/research/2026-02-14-mongodb-schema-decision.md

MongoDB Schema Design Decision Summary

Date: 2026-02-14 Decision: Zero-Knowledge Encryption for All Sensitive Data + Metadata

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Core Principle

ALL sensitive data AND metadata must be encrypted client-side before reaching MongoDB.

Example: Blood Pressure Reading

Before encryption (client-side):

{
  value: "120/80",
  type: "blood_pressure",
  unit: "mmHg",
  date: "2026-02-14T10:30:00Z"
}

After encryption (stored in MongoDB):

{
  healthDataId: "health-123",
  userId: "user-456",
  profileId: "profile-789",
  familyId: "family-012",
  
  // Encrypted (value + metadata)
  healthData: [
    {
      encrypted: true,
      data: "a1b2c3d4...",
      iv: "e5f6g7h8...",
      authTag: "i9j0k1l2..."
    }
  ],
  
  // Metadata (plaintext)
  createdAt: ISODate("2026-02-14T10:30:00Z"),
  updatedAt: ISODate("2026-02-14T10:30:00Z"),
  dataSource: "healthKit"
}

---

Collections Summary

Collection	Purpose	Encrypted Fields	Plaintext Fields
users	Authentication	encryptedRecoveryPhrase	userId, email, passwordHash, tokenVersion, familyId, familyRole, permissions
families	Family structure	familyName, familyMetadata	familyId, members[].userId, members[].profileId, members[*].role
profiles	Person profiles	profileName, profileMetadata	profileId, userId, familyId, profileType
health_data	Health records	healthData[*] (value + metadata)	healthDataId, userId, profileId, familyId, createdAt, updatedAt, dataSource
lab_results	Lab tests	labData (value + metadata), labMetadata	labResultId, userId, profileId, familyId, createdAt, updatedAt, dataSource
medications	Medication tracking	medicationData (value + metadata), reminderSchedule	medicationId, userId, profileId, familyId, active, createdAt, updatedAt
appointments	Medical appointments	appointmentData (value + metadata), reminderSettings	appointmentId, userId, profileId, familyId, createdAt, updatedAt
shares	Shared data	encryptedData (share-specific password)	shareId, userId, documentId, collectionName, createdAt, expiresAt, accessCount, isRevoked
refresh_tokens	JWT tokens	None	jti, userId, createdAt, expiresAt, revoked

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Encryption Strategy

Client-Side Encryption

Encryption Flow:

1. User enters health data
2. Client derives encryption key from password (PBKDF2)
3. Client encrypts health data (AES-256-GCM)
4. Client sends encrypted data to server
5. Server stores encrypted data in MongoDB
6. Server NEVER decrypts data

What Must Be Encrypted

• ✅ Health data values (e.g., "120/80")
• ✅ Health data metadata (e.g., "blood_pressure", "mmHg")
• ✅ Lab test results (e.g., "cholesterol", "200", "LabCorp")
• ✅ Medication data (e.g., "Aspirin", "100mg", "daily")
• ✅ Appointment data (e.g., "checkup", "Dr. Smith")
• ✅ Profile data (e.g., "John Doe", "1990-01-01")
• ✅ Family data (e.g., "Smith Family", "123 Main St")

What Can Be Plaintext

• ✅ User IDs (userId, profileId, familyId) - for queries
• ✅ Email addresses - for authentication
• ✅ Dates (createdAt, updatedAt) - for sorting
• ✅ Data sources (healthKit, googleFit) - for analytics
• ✅ Tags (cardio, daily) - for client-side search

---

Privacy-Preserving Queries

1. Plaintext Queries (Recommended)

Query by plaintext fields only:

const healthData = await db.health_data.find({
  userId: 'user-123',    // Plaintext ✅
  profileId: 'profile-456',  // Plaintext ✅
  familyId: 'family-789'     // Plaintext ✅
}).toArray();

// Client decrypts healthData[i].healthData[j]

2. Tagging System (Encrypted Search)

Client adds searchable tags to encrypted data:

const healthData = await db.health_data.find({
  userId: 'user-123',
  tags: { $in: ['cardio', 'daily'] }  // Plaintext tags ✅
}).toArray();

// Client decrypts healthData[i].healthData[j]

3. Date Range Queries (Plaintext Dates)

Store dates as plaintext (for range queries):

const healthData = await db.health_data.find({
  userId: 'user-123',
  date: {
    $gte: ISODate("2026-02-01"),
    $lte: ISODate("2026-02-28")
  }
}).toArray();

// Client decrypts healthData[i].healthData[j]

---

Technology Stack

Backend (Axum + MongoDB)

• Axum 0.7.x: Web framework
• MongoDB 6.0+: Database
• Rust: Server language

Client (React Native + React)

• AES-256-GCM: Encryption algorithm
• PBKDF2: Key derivation function
• Crypto API: Node.js crypto / react-native-quick-crypto

---

Implementation Timeline

• Week 1: Create MongoDB indexes
• Week 1-2: Implement client-side encryption (React Native + React)
• Week 2-3: Implement server-side API (Axum + MongoDB)
• Week 3: Test encryption flow
• Week 3-4: Test data migration (key rotation)
• Week 4: Test privacy-preserving queries
• Week 4-5: Performance testing Total: 4-5 weeks

---

Next Steps

1. Create MongoDB indexes for all collections
2. Implement client-side encryption (React Native + React)
3. Implement server-side API (Axum + MongoDB)
4. Test encryption flow (end-to-end)
5. Test data migration (key rotation)
6. Test privacy-preserving queries
7. Performance testing
8. Create API documentation

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References

• Comprehensive MongoDB Schema Research
• Normogen Encryption Guide
• JWT Authentication Research
• Technology Stack Decisions