Proton's crypto is not Transparent and not OPAQUE
The article argues Proton's authentication uses SRP, not truly transparent or OPAQUE cryptography, despite marketing claims. It explains that SRP reveals a password verifier to the server, unlike OPAQUE which fully hides the password from the server.
Background
- Proton is a Swiss company best known for Proton Mail, an encrypted email service. It also offers VPN, cloud storage, and other privacy-focused tools.
- This post is part of a continuing debate between Proton and its critics about the trustworthiness of its encryption. The author, Marc Schärli, is a Swiss security engineer who has been publicly critical of Proton’s cryptographic choices.
- The author argues that Proton’s new cryptographic protocol, which it calls “Transparent” (for password management) and “OPAQUE” (a related protocol), misleads users. OPAQUE is a real academic protocol, but the author claims Proton’s implementation is neither truly transparent nor OPAQUE-compliant, weakening the privacy guarantees users expect.
- This matters because Proton markets itself as a privacy-first company; if its cryptography has flaws or deceptive naming, users may trust it with sensitive data under false assumptions. The debate reflects wider tensions between usable security, marketing, and cryptographic rigor.