Analysis of ProtonMail Cryptographic Architecture

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Cryptology ePrint Archive: Report 2018/1121

An Analysis of the ProtonMail Cryptographic Architecture
Nadim Kobeissi

Abstract: ProtonMail is an online email service that claims to offer
end-to-end encryption such that "even [ProtonMail] cannot read and
decrypt [user] emails." The service, based in Switzerland, offers
email access via webmail and smartphone applications to over five
million users as of November 2018. In this work, we provide the first
independent analysis of ProtonMail's cryptographic architecture. We
find that for the majority of ProtonMail users, no end-to-end
encryption guarantees have ever been provided by the ProtonMail
service and that the "Zero-Knowledge Password Proofs" are negated by
the service itself. We also find and document weaknesses in
ProtonMail's "Encrypt-to-Outside" feature. We justify our findings
against well-defined security goals and conclude with recommendations.

Category / Keywords: applications / public-key cryptography, pgp

Date: received 18 Nov 2018, last revised 19 Nov 2018
Contact author: nadim at symbolic software
Available format(s): PDF | BibTeX Citation
Version: 20181120:032816 (All versions of this report)
Short URL: ia.cr/2018/1121

https://eprint.iacr.org/2018/1121.pdf