Zero-Knowledge Security

Vault implements a zero-knowledge architecture where your data remains encrypted end-to-end. The server never has access to your plaintext passwords.

What is Zero-Knowledge?

Zero-knowledge means the server:

Never sees your master password
Never sees your vault key
Never sees your decrypted entries
Cannot decrypt your data even if compromised

┌─────────────────────────────────────────────────────────────────┐
│                        Your Device                               │
│  ┌──────────┐   ┌──────────┐   ┌──────────┐                     │
│  │ Master   │──▶│ Derive   │──▶│ Decrypt  │──▶ Plaintext        │
│  │ Password │   │ Keys     │   │ Entries  │   Passwords         │
│  └──────────┘   └──────────┘   └──────────┘                     │
└─────────────────────────────────────────────────────────────────┘
        │                               │
        │ Never transmitted             │ Never transmitted
        ▼                               ▼
┌─────────────────────────────────────────────────────────────────┐
│                        Vault Server                              │
│  ┌──────────┐   ┌──────────┐   ┌──────────┐                     │
│  │ Wrapped  │   │ Encrypted │   │ WebAuthn │                    │
│  │ Vault Key│   │ Vault     │   │ Credential│                   │
│  └──────────┘   └──────────┘   └──────────┘                     │
└─────────────────────────────────────────────────────────────────┘

Security Model

Client-Side Encryption

All encryption and decryption happens on your device:

Master Password → Never leaves your device
Key Derivation → PBKDF2 runs locally
Vault Encryption → AES-GCM encryption runs locally
Vault Decryption → Only your device can decrypt

What the Server Stores

Data	Encryption	Server Access
Email	Plaintext	✅ Required for login
WebAuthn Credential	Signed	✅ Required for passkey auth
Wrapped Vault Key	Encrypted	❌ Cannot decrypt
Encrypted Vault	AES-GCM	❌ Cannot decrypt
PBKDF2 Salt	Plaintext	⚠️ Useless without password

What Stays Local

Data	Storage	Persisted
Master Password	Memory only	Never
Vault Key	Memory only	Never
Decrypted Entries	Memory only	Never
Derived KEK	Memory only	Never

Threat Model

What We Protect Against

✅ Server Breach - Attacker gets database dump

All vault data is encrypted
No master passwords stored
WebAuthn credentials require physical authenticator

✅ Man-in-the-Middle - Attacker intercepts traffic

HTTPS/TLS encryption in transit
Data already encrypted before transmission
WebAuthn prevents phishing

✅ Malicious Server - Server operator turns evil

Cannot decrypt vault data
Cannot derive master passwords from salts
Cannot forge WebAuthn authentication

What Requires User Vigilance

⚠️ Weak Master Password - Brute-force attack on wrapped key

Use strong, unique master password
Salt + PBKDF2 provides some protection

⚠️ Compromised Device - Malware on your machine

Master password exposed in memory
Use device security features
Enable biometric unlock to avoid typing password

⚠️ Social Engineering - Tricked into revealing credentials

Never share your master password
Verify you're on the real Vault domain

Cryptographic Primitives

Purpose	Algorithm	Key Size
Key Derivation	PBKDF2-SHA256	256-bit
Vault Encryption	AES-256-GCM	256-bit
Key Wrapping	AES-256-GCM	256-bit
Authentication	WebAuthn ECDSA	P-256
Sharing	ECDH P-256	256-bit

Security Sections

Encryption

How vault encryption works with AES-GCM and key derivation.

Passkeys

WebAuthn/Passkey authentication and why it's phishing-resistant.

ECDH Sharing

How vault sharing maintains zero-knowledge properties.

Audit Status

Component	Status	Notes
Crypto Library	✅ Web Crypto API	Browser-native, FIPS-validated
Server Code	🔄 Pending	Community review welcome
Client Code	🔄 Pending	Open source on GitHub

Best Practices

Master Password

Use 12+ characters with mixed case, numbers, symbols
Or use a 5+ word passphrase
Never reuse across services
Consider writing down and storing securely

Biometrics

Enable Touch ID / Face ID when available
Reduces keyboard exposure of master password
Still requires master password as fallback

Backup

Test that you can unlock with master password
Store master password backup securely offline
Recovery without master password is impossible