This paper evaluates the implementation of the RSA-2048 algorithm within Telegram’s MTProto protocol. Unlike standard applications, Telegram utilizes RSA exclusively for initial server authentication and the exchange of Diffie-Hellman parameters, rather than direct message encryption. The analysis identifies critical security risks stemming from Telegram’s use of a custom padding scheme (RSAPAD) instead of the industry-standard OAEP. This non-standard approach has exposed the protocol to timing side-channel attacks and message malleability. Furthermore, a comparative study with the Signal Protocol reveals that Telegram’s architecture—which stores long-term keys on servers—sacrifices Perfect Forward Secrecy (PFS) and absolute privacy for multi-device convenience. The findings suggest that Telegram’s
Sao et al. (Thu,) studied this question.