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Proton Authenticator vs Duo Mobile: catalog facts
Proton Authenticator	Duo Mobile
Free Free and open source under the GPL, with no advertising. A Proton account is used for…	Free The app is free. The Duo service behind it is a paid product for organisations.
Windows, Linux, Android, iOS	Android, iOS
End-to-end encrypted sync between devices, which most free authenticators lack Apps for Android, iOS, Windows, Linux and macOS	Verified Push defeats the push-fatigue attacks that plague plain approvals Also works as an ordinary TOTP authenticator for other accounts
Sync requires a Proton account Keeping codes on the same desktop you log in from weakens second-factor separation	Built around a Duo deployment that an organisation pays for Closed source
Downloadable app	Downloadable app
Open source	Closed source
License: GPL-3.0	License not stated
No account needed	Not stated if an account is needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 22, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.