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od1n
od1n

Posted on • Originally published at vault-local.vercel.app

Building a Zero-Knowledge Password Manager with Rust and Tauri 2.0

#rust #security #tauri #opensource

LastPass was breached in 2022. 33 million encrypted vaults ended up in attackers' hands. The root cause? Your passwords lived on their servers.

I decided to build a password manager where that scenario is architecturally impossible — because there is no server.

This is how I built Vault Local: a local-first, zero-knowledge password manager using Rust, Tauri 2.0, and modern cryptography.

The Architecture

The core principle: your data never leaves your computer. There's no cloud, no sync server, no account creation. Just one encrypted file on your disk.

Master Password
      │
      ▼
  Argon2id (19 MiB RAM, 2 iterations)
      │
      ▼
  HKDF-SHA256
      ├──────────────────┐
      ▼                  ▼
  db_key             enc_key
  (SQLCipher)        (XChaCha20-Poly1305)
      │                  │
      ▼                  ▼
  Encrypts entire    Encrypts individual
  database file      credential fields
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Two independent keys derived from the same master password, but cryptographically separated via HKDF with different info strings. Even if SQLCipher were somehow compromised, the field-level encryption remains intact.

Why Rust?

The ownership system prevents the exact class of bugs that plague password managers:

  • No buffer overflows — Rust's borrow checker eliminates them at compile time
  • No use-after-free — the compiler enforces lifetimes
  • Deterministic cleanup — Drop runs exactly when a value goes out of scope, which matters when that value is an encryption key

For cryptographic secrets, I use the zeroize and secrecy crates:

use zeroize::{Zeroize, ZeroizeOnDrop};
use secrecy::Secret;

#[derive(Zeroize, ZeroizeOnDrop)]
pub struct EncKey(pub [u8; 32]);

pub struct VaultState {
    pub connection: Connection,
    pub enc_key: Secret<EncKey>,  // Auto-zeroized on drop
}
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When the vault locks, VaultState drops, and the encryption key is overwritten with zeros in memory. No garbage collector, no "maybe the runtime will clean it up eventually."

Why Tauri 2.0 over Electron?

Electron Tauri 2.0
Installer size ~150 MB 4.6 MB
Runtime Bundles Chromium Uses system WebView
Backend Node.js (JS) Rust (native)
Security model Full filesystem access Principle of least privilege
IPC Unrestricted Explicit command registration

Tauri's security model is the key differentiator. The web frontend cannot access the filesystem, network, or system APIs. Every capability must be explicitly declared:

{
  "permissions": ["core:default", "dialog:default"]
}
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The frontend communicates with the Rust backend exclusively through typed commands:

#[tauri::command]
pub fn get_entry(
    state: tauri::State<'_, AppState>,
    id: String,
) -> Result<Entry, String> {
    // Decrypt and return entry
}
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// Frontend — this is the ONLY way to access data
const entry = await invoke<Entry>('get_entry', { id });
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The Encryption Stack

Key Derivation: Argon2id

Argon2id won the Password Hashing Competition. It's memory-hard, meaning it requires a fixed amount of RAM to compute — making GPU/ASIC attacks impractical:

let params = Params::new(
    19456,  // 19 MiB of RAM
    2,      // 2 iterations
    1,      // 1 degree of parallelism
    Some(32) // 32 bytes output
)?;

let argon2 = Argon2::new(Algorithm::Argon2id, Version::V0x13, params);
argon2.hash_password_into(password, salt, &mut master_key)?;
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Symmetric Encryption: XChaCha20-Poly1305

I chose XChaCha20-Poly1305 over AES-256-GCM for a specific reason: the extended nonce.

  • AES-256-GCM: 96-bit nonce → collision risk after ~2^32 encryptions with the same key
  • XChaCha20-Poly1305: 192-bit nonce → safe for virtually unlimited encryptions

For a long-lived local vault where the same key encrypts thousands of entries over years, the larger nonce margin is significant.

pub fn encrypt(key: &[u8; 32], plaintext: &[u8]) -> Result<Vec<u8>, String> {
    let cipher = XChaCha20Poly1305::new(key.into());
    let mut nonce_bytes = [0u8; 24];
    OsRng.fill_bytes(&mut nonce_bytes);
    let nonce = XNonce::from_slice(&nonce_bytes);

    let ciphertext = cipher.encrypt(nonce, plaintext)?;

    // Store as: nonce (24 bytes) || ciphertext
    let mut result = Vec::with_capacity(24 + ciphertext.len());
    result.extend_from_slice(&nonce_bytes);
    result.extend_from_slice(&ciphertext);
    Ok(result)
}
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Database Encryption: SQLCipher

SQLCipher is a fork of SQLite that encrypts the entire database file with AES-256-CBC + HMAC-SHA256. Every page is encrypted independently.

pub fn open_db(db_path: &Path, db_key: &[u8; 32]) -> Result<Connection, String> {
    let conn = Connection::open(db_path)?;
    let hex_key = hex::encode(db_key);
    conn.execute_batch(&format!("PRAGMA key = \"x'{}'\";", hex_key))?;
    // Verify the key works
    conn.execute_batch("SELECT count(*) FROM sqlite_master;")?;
    Ok(conn)
}
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Browser Extension via Native Messaging

The browser extension doesn't store any credentials. It communicates with the desktop app through Chrome's Native Messaging protocol:

Extension popup → Native Messaging Host (Node.js) → TCP localhost:51820 → Rust IPC Server
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The IPC server only listens on 127.0.0.1 and requires a token that regenerates on every vault unlock. No external network access.

What I Learned

  1. Tauri 2.0 is production-ready for security-sensitive apps. The permission model is genuinely useful.

  2. SQLCipher's bundled-sqlcipher-vendored-openssl feature in rusqlite compiles OpenSSL from source. It requires Perl on Windows (Strawberry Perl). Plan for this in your build pipeline.

  3. The zeroize crate can't clear CPU registers — it's a fundamental limitation. But it handles heap and stack memory correctly, which covers the vast majority of attack surface.

  4. XChaCha20 is constant-time without hardware support, unlike AES which relies on AES-NI for timing-attack resistance. This matters for cross-platform software where you can't guarantee hardware features.

  5. Native Messaging on Windows requires a .bat wrapper — Node.js .js files can't be executed directly as native messaging hosts. A one-line batch file solves it.

Try It

Vault Local is free and open source (MIT):

Features include: password audit with HIBP breach check, TOTP authenticator, SSH agent, import from 8 formats (Chrome, Firefox, Bitwarden, 1Password, LastPass, KeePass), encrypted sync, browser extension, and passkey storage.

Built with ~15,000 lines of Rust + TypeScript across ~70 files. I'd appreciate any feedback, especially on the cryptographic implementation.

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