An encrypted messenger you can lock with a YubiKey

ZeroMem (零憶) is an end-to-end encrypted messenger for Android and Windows. Your identity is a key that exists only on your own device. Your passphrase always protects it, and you choose what is added to it:

• bound to your device's security chip, so a copied identity file cannot be opened on another machine,
• or locked with a FIDO2 security key such as a YubiKey, so it opens only with your passphrase plus the key.

How the security key works

Add it in Settings, under Protection and unlock: plug the key into the computer, or hold it against the back of the phone, then enter its PIN and touch it. From then on the identity file needs your passphrase plus the key to open. You can add up to four keys and keep a spare somewhere safe.

It needs a FIDO2 key that supports hmac-secret, such as YubiKey 5 (firmware 5.7 or later) or Nitrokey 3. On a computer, Windows 11 or a recent Windows 10 is needed.

Why it matters

A messenger account is only as safe as the key behind it. With a security key added, a copy of your identity file is useless on its own: it cannot be opened, and your passphrase cannot even be guessed offline. On the device itself, five wrong passphrases destroy the identity.

Know who is on the other end

Your key protects your side. To be sure of the other side, compare your 60-digit safety code in person or scan each other's code. Verified contacts show a shield, and the app tells you when a contact's identity changes.

What else ZeroMem does

• End-to-end encrypted messages, files and one-to-one and group voice calls.
• Messages live in memory: the app never saves a conversation on the device.
• A voice changer for calls, on by default, so what the other side hears and records is not your real voice.
• Contact only by consent: add people by username or code; both sides agree first.