Reason to believe is that all their apps are open source and have reproducible builds: https://core.telegram.org/reproducible-builds https://core.telegram.org

Reason to believe is that all their apps are open source and have reproducible builds: https://core.telegram.org/reproducible-builds https://core.telegram.org/reproducible-builds Their custom encryption is questionable, but since it open source someone would find out by now if there was obvious backdoors.