What is a zero-knowledge password manager?

“Zero-knowledge” is one of the most abused phrases in security marketing. Almost every password manager claims it. Most have genuinely earned it, and it still isn’t the whole story.

A zero-knowledge password manager is one whose provider can never read your secrets: your data is encrypted on your device, and the server only ever sees ciphertext. It’s a strong, real property. But zero-knowledge still means there’s an encrypted vault sitting on a server somewhere. MoolKey takes a different route: it does not store generated passwords or PINs to encrypt in the first place.

What “zero-knowledge” actually means

In a zero-knowledge architecture, encryption and decryption happen entirely on your device. A key derived from your master password, which is never sent anywhere, encrypts your vault before it leaves your machine. The provider stores and syncs only the resulting ciphertext, and cannot decrypt it even if compelled to.

Reputable vaulted managers like 1Password and Bitwarden are genuinely zero-knowledge in this sense. It’s a meaningful guarantee, and a good baseline to demand from any tool that holds your data.

Zero-knowledge is not zero-risk

Here’s the catch: the encrypted vault still exists, and “we can’t read it” is a statement about today’s math. Steal the blob and an attacker can grind on it offline indefinitely, as hardware improves and as any weak master password becomes the soft spot.

This isn’t hypothetical. When investigators linked the theft of more than $150 million in cryptocurrency to the 2022 LastPass breach, the stolen vaults were zero-knowledge encrypted, and still became the root of the loss. Encryption bought time, not immunity.

MoolKey’s version: nothing to know

MoolKey is zero-knowledge in the strict sense and then takes a different route, because there is no vault of generated credentials. Passwords are recomputed on demand from a few inputs plus your Master Key. The service keeps non-secret account metadata along with authentication and security records.

Two secrets exist, and they’re handled very differently:

• Your master key never leaves your device, is never stored or transmitted, and is cleared from memory shortly after use. It’s the seed for every derived password.
• Your login password (used only to reach the account-metadata service) is stored as a bcrypt hash (cost factor 12) on the server, never in plaintext.

And recognized email or phone account identifiers are masked before persistence. The login email used for authentication and free-form labels have a different storage role, so the service is not blind to every piece of account data.

What’s stored vs what’s never stored

What MoolKey stores and never stores

MoolKey stores (non-secret)	MoolKey never stores
Login email and a bcrypt hash of the login password	Your Master Key
Masked email or phone account identifiers	Your Shared Key
Canonical app names and per-account settings	Any generated password or PIN
Sharing, notification, audit, and session-security records	An encrypted vault of generated credentials

A breach of a zero-knowledge vault can leak an encrypted copy of your secrets. A breach of MoolKey does not yield a stored list of generated credentials, but it can expose the non-secret account metadata and security records the backend keeps. That’s the difference between “can’t read it yet” and “no generated credential list to decrypt.”

The honest limits

Zero-knowledge of any kind asks for some trust, and so does this:

• You’re trusting the client to derive correctly and not leak. That trust is unavoidable with any password tool, but here it is at least checkable: because derivation is deterministic and the algorithm is documented, you can verify by hand that the same inputs always produce the same password, on any device, with the network switched off.
• The stored metadata still reveals which services you hold accounts on, in masked form.
• No vault means no account recovery and nowhere to keep arbitrary secrets. That’s the deliberate trade we made, and we’d rather state it than bury it.

In short

• Zero-knowledge = the provider holds only ciphertext and can’t decrypt it.
• It’s real and worth demanding, but the encrypted blob can still be stolen and attacked offline.
• MoolKey does not store generated passwords or PINs: it recomputes them, while the Master Key stays on your device.
• A breach does not reveal a stored credential list, but backend metadata and security records still matter.

Frequently asked questions

Is MoolKey a zero-knowledge password manager? It follows the usual provider-blind model for generated credentials and avoids storing a vault of them. The server does keep account metadata and authentication or security records, but it does not receive the Master Key or generated password.

What can MoolKey’s servers actually see? Masked identifiers, canonical app names, per-account version integers, and a bcrypt hash of your login password. They never see your master key or any derived password, because those are never sent.

Does zero-knowledge mean my passwords can’t be stolen? Not on its own. In a vaulted design it means they can’t be read today, but the encrypted copy can be stolen and attacked over time. MoolKey does not keep a server-side copy of generated credentials, but a compromised device or exposed Master Key can still put accounts at risk.

Is zero-knowledge the same as end-to-end encrypted? They overlap: both keep plaintext on your devices and ciphertext in transit and at rest. The key idea in both is that the provider never holds the decryption key. MoolKey shares the goal but reaches it by never persisting a secret at all.

See the full, line-by-line comparison against vaulted managers, or read how the model works.