Basically, the problem is that they invented a lot of their own crypto from scratch. When asked about this, they said "it's fine, we're smart" and then claimed

Basically, the problem is that they invented a lot of their own crypto from scratch. When asked about this, they said "it's fine, we're smart" and then claimed to prove their security with a red herring contest. Here are some publications about security problems with the platform: - A class project at MIT found several problems (May 2017) [0] - They were featured on Crypto Fails (Dec 2013) [1] - Jakob Jakobsen @ Aarhus University published a vulnerability discovery (May 2015) [2] and then did his Masters thesis on additional problems (Sep 2015) [3] -Tomas Susanka @ Czech Technical University in Prague published additional vulnerabilities (2016) [4] Plenty more out there. [0] https://courses.csail.mit.edu/6.857/2017/project/19.pdf https://courses.csail.mit.edu/6.857/2017/project/19.pdf [1] http://www.cryptofails.com/post/70546720222/telegrams-cryptanalysis-contest http://www.cryptofails.com/post/70546720222/telegrams-crypta... [2] https://eprint.iacr.org/2015/1177.pdf https://eprint.iacr.org/2015/1177.pdf [3] http://cs.au.dk/~jakjak/master-thesis.pdf http://cs.au.dk/~jakjak/master-thesis.pdf [4] https://www.susanka.eu/files/telegram-article.pdf https://www.susanka.eu/files/telegram-article.pdf