Security & encryption
How Zecuri protects your vault — a detailed, plain-English technical overview.
Threat model & assumptions
Zecuri protects against:
- Server compromise: if attackers gain access to our servers and all sync metadata, they learn nothing about your passwords. Vault data is encrypted with keys derived from your master password.
- Network eavesdropping: all communication is over HTTPS. Even if traffic is intercepted, vault data is end-to-end encrypted with AES-256-GCM.
- Account enumeration: our servers don't store account names or emails — only sync metadata. An attacker cannot enumerate Zecuri users.
Zecuri does not protect against:
- Device compromise (malware): a keylogger on your device can capture your master password.
- Physical device theft: if someone steals your device and cracks the device lock, they can reach your vault.
- Social engineering: if you're tricked into revealing your master password, an attacker can access your vault.
Bottom line: Zecuri moves the responsibility to the device level. Keep your device secure — OS updates, a strong passcode — and Zecuri handles the encryption.
Cryptographic primitives
Modern, standard, audited building blocks — nothing home-grown in the critical path.
Master password derivation
Argon2id (RFC 9106)m=64 MiB, t=3, p=4. 32-byte random salt per account, 32-byte output key. Memory-hard, resistant to GPU/ASIC cracking. No shared master key across accounts.
Vault encryption
AES-256-GCM12-byte random nonce per encryption; authenticated encryption detects tampering. Each item is encrypted separately, so one compromised key doesn't expose the rest.
Device signing
Ed2551932-byte keys, 64-byte signatures. Each device signs its sync metadata; other devices verify signatures for integrity. Fast and side-channel resistant.
Cross-device sync without a central key
Zecuri sync works like a time machine for your vault:
- Each device keeps a log of changes — password added, updated, or deleted.
- Each change is stamped with a Hybrid Logical Clock (HLC) timestamp.
- When devices sync, they exchange change logs.
- Each device merges changes using a Last-Write-Wins (LWW) strategy.
- If two devices modify the same password at different times, the later change wins.
- If they modify it concurrently, the device with the higher ID wins — deterministically.
The server only ever holds Ed25519-signed sync metadata — never your vault contents. Devices do the encryption and merging; the server is stateless.
Security audit & transparency
Zecuri's security is verified through:
- Dependency CVE scan: every dependency is checked against the NIST CVE database.
- Threat-model review: assumptions documented and reviewed against the OWASP Top 10.
- Code review: sync and crypto code reviewed for timing attacks, buffer overflows, and logic errors.
- Standard primitives: all cryptography is NIST-approved or widely recommended.
- Open source: all critical-path code is public. No closed-source components in the crypto.
What's next (roadmap)
- OPAQUE-3DH migration: replace token exchange with OPAQUE password-authenticated key exchange, so no password material (even hashed) is sent over the wire.
- Per-item key derivation: researching whether each item should have its own derived key (extra isolation for marginal cost).
- Durable storage migration: moving sync state to durable storage for permanent retention beyond the current short-lived cache.
Encryption you can verify
Read the code, run the audit, then install with confidence.