International Association
for Cryptologic Research

Recently, there has been an increase in the popularity of messaging applications that use end-to-end encryption. Among them were Telegram (in October 2021 it has 550 million active users), Signal (in January 2022 it has over 50 million downloads in the Google Play Store), WhatsApp (according to Statista, in 2021 it has over 2 billion active users), Wire (until January 2022 it has been downloaded for over 1 million times on Android devices). Two distinct protocols underlying these applications are noted: MTProto (developed in Russia by Nikolai Durov) and Signal (developed in the US by Moxie Marlinspike). This paper presents the two protocols and examines from the point of view of the primitive cryptographic security used and how the authenticated encryption, key derivation and asynchronous messaging are performed.