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Automated Symbolic Verification of Telegram’s MTProto 2.0. (arXiv:2012.03141v2 [cs.CR] UPDATED)

MTProto 2.0 is a suite of cryptographic protocols for instant messaging at
the core of the popular Telegram messenger application. In this paper we
analyse MTProto 2.0 using the symbolic verifier ProVerif. We provide fully
automated proofs of the soundness of MTProto 2.0’s authentication, normal chat,
end-to-end encrypted chat, and rekeying mechanisms with respect to several
security properties, including authentication, integrity, secrecy and perfect
forward secrecy; at the same time, we discover that the rekeying protocol is
vulnerable to an unknown key-share (UKS) attack. We proceed in an incremental
way: each protocol is examined in isolation, relying only on the guarantees
provided by the previous ones and the robustness of the basic cryptographic
primitives. Our research proves the formal correctness of MTProto 2.0 w.r.t.
most relevant security properties, and it can serve as a reference for
implementation and analysis of clients and servers.