# Security & Cryptography Specification

## 1. Master Key Derivation & Credential Management

- **Key Derivation Function**: Argon2id
  - Memory: 64 MB (65536 KiB)
  - Time Cost / Iterations: 3
  - Parallelism: 4 threads
  - Salt: Cryptographically secure random 16 bytes generated per initialization.
- **Key Ring Integration**:
  - **Windows**: Encrypted via DPAPI (CryptProtectData) and stored in Windows Credential Manager.
  - **Linux**: Managed via SecretService API (libsecret / Freedesktop SecretService DBus).
  - **Android**: Generated inside Android KeyStore backed by Hardware-backed Trusted Execution Environment (TEE) / StrongBox.

## 2. Local Database Encryption

- **Engine**: SQLCipher 4.x
- **Cipher Algorithm**: AES-256-CBC
- **Key Derivation**: PBKDF2-HMAC-SHA512 (256,000 iterations default for SQLCipher 4).
- **Page Authentication**: HMAC-SHA512 per page.

## 3. P2P Mesh Network Encryption

- **Transport Security Protocol**: Noise Protocol Framework (Noise_XK_25519_ChaChaPoly_BLAKE2s).
- **Authentication**: Pre-shared 256-bit **Swarm Key** combined with Ed25519 node identity keys.
- **Peer Exchange Cipher**: Ephemeral Diffie-Hellman (X25519) key exchange + ChaCha20-Poly1305 AEAD payload ciphering.