What Is a Zero-Knowledge Password Manager?
By Harshil Kachhadiya · Updated · 5 min read
A zero-knowledge password manager is built so that the company running it cannot read your passwords, even if it wanted to or its servers were breached. Here is how that works and why it matters.
The core idea: encrypt before you upload
In a traditional cloud service, your data travels to the provider's servers and is protected there. In a zero-knowledge design, your data is encrypted on your own device first, using a key the provider never receives. The server stores only ciphertext, a scrambled blob that is meaningless without that key.
The key is derived from your master password. Because the master password is never transmitted or stored by the provider, the provider has nothing it could use to decrypt your vault.
How the key is created
Padlock runs your master password through PBKDF2-SHA-256 with a random salt and 600,000 iterations for new vaults. This key derivation is deliberately slow, which makes guessing attacks expensive. The result is a 256-bit key used with AES-256-GCM, an authenticated encryption mode that detects tampering as well as hiding content.
All of this happens locally using the browser's built-in Web Crypto API. Nothing about the master password or the derived key is sent over the network.
What the server can and cannot see
A zero-knowledge service still needs to store some information so the product works. In Padlock, the site name, URL, and username are stored as readable text so entries can be listed and matched to the right website. Passwords, TOTP secrets, and secure notes are stored only as ciphertext.
- Cannot see: your master password, your encryption key, saved passwords, TOTP secrets, note contents.
- Can see: your account email, site names and URLs, usernames, and when entries were created or changed.
The trade-off: no password recovery
If the provider cannot decrypt your vault, it also cannot help you if you forget the master password. There is no reset link that restores your data. This is not a flaw, it is the direct consequence of the privacy guarantee. Choose a master password you can remember and keep a written copy somewhere safe.
Is zero-knowledge enough on its own?
It protects you from a provider breach and from insider access, but it does not protect a weak master password from being guessed, or a compromised device from leaking what you type. Use a long, unique master password, keep your browser and operating system updated, and turn on two-factor authentication for your most important accounts.