d7d09482da
Records the decision: client-side AES-256-GCM, double-PBKDF2 auth/enc-key split, server-as-blind-store, in-memory key lifecycle, and Phase 1 limitations (forgotten password = data loss; Phase 2 recovery wrapping deferred).
69 lines
2.7 KiB
Markdown
69 lines
2.7 KiB
Markdown
# ADR: Zero-Knowledge Encryption (Phase 1)
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**Status**: Implemented (Phase 1)
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**Date**: 2026-06-28
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## Context
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The original design (`docs/product/encryption.md`, `docs/adr/mongodb-schema-decision.md`)
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specified client-side zero-knowledge encryption: the server should never hold
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plaintext user data or encryption keys. Until this change, the `EncryptedField`
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type and recovery-phrase fields were aspirational scaffolding — data was always
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stored and processed as plaintext JSON.
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## Decision
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Implement **client-side zero-knowledge encryption** using AES-256-GCM via the
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browser's Web Crypto API. The server becomes a blind store: it holds opaque
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ciphertext and can never decrypt user data.
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### Key derivation: double PBKDF2
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From the user's password, the client derives two independent values:
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- **Auth secret**: `PBKDF2(password, "normogen-auth-v1", 150k iters, SHA-256)` →
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base64, sent to the server as the "password". The server PBKDF2-hashes it
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(as before).
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- **Encryption key**: `PBKDF2(password, "normogen-enc-v1", 150k iters, SHA-256)` →
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AES-GCM `CryptoKey`, kept in memory only, never transmitted.
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The server cannot derive the encryption key because it never sees the raw
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password or the enc-domain PBKDF2 output.
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### What's encrypted
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- Medication data blobs (name, dosage, frequency, route, etc.)
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- Appointment data blobs (title, provider, date/time, etc.)
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- Profile display name
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### What stays plaintext (queryable)
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- IDs (`medicationId`, `appointmentId`, `userId`, `profileId`)
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- Medication `active` flag (top-level, filterable)
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- Appointment `status` (top-level, filterable)
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- Timestamps
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### In-memory key lifecycle
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The encryption key lives only in browser memory for the authenticated session.
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It is NOT persisted. A page reload requires re-entering the password to
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re-derive it. This is the core ZK trade-off.
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## Consequences
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### Phase 1 limitations (documented)
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- **Forgotten password = data loss.** No recovery key-wrapping yet (Phase 2).
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- **Page reload requires re-authentication** to re-derive the enc key.
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- No data migration was needed (no real user data existed).
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### Phase 2 (future)
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- Recovery key-wrapping (wrap the enc key under a recovery-derived key so a
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forgotten password doesn't lose data).
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- Password-change re-wrapping (re-wrap the enc key under the new password).
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- Wrapped-DEK model (separate data-encryption key + key-encryption key).
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## Relationship to the original design doc
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`docs/product/encryption.md` describes a fuller zero-knowledge architecture
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(per-user keys, deterministic encryption for search, key rotation). This Phase 1
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implements the core property (server can't read data) with the simplest viable
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design. The fuller features remain future work.
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