Implements the complete user engine for multi-recipient envelope encryption:
- ECDH key agreement (X25519, P-256, P-384) with HKDF-derived wrapping keys
- Per-message random DEK wrapped individually for each recipient
- 9 operations: register, provision, get-public-key, list-users, encrypt,
decrypt, re-encrypt, rotate-key, delete-user
- Auto-provisioning of sender and recipients on encrypt
- Role-based authorization (admin-only provision/delete, user-only decrypt)
- gRPC UserService with proto definitions and REST API routes
- 16 comprehensive tests covering lifecycle, crypto roundtrips, multi-recipient,
key rotation, auth enforcement, and algorithm variants
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Kyle Isom
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