"roll your own" has no official definition I'm aware of, so I'm not sure what you mean by "technically" incorrect. This could quickly become a discussion of sem

"roll your own" has no official definition I'm aware of, so I'm not sure what you mean by "technically" incorrect. This could quickly become a discussion of semantics unfortunately. To be specific with what I mean, it is "roll your own" in the sense that 1) their protocol combines cryptographic primitives in unrecommended ways with no particular justification and in the sense that 2) they literally have invented and written many of these primitives themselves. As a concrete example, the IGE mode used by Telegram for AES is not "well known", in fact to the best of my knowledge Telegram is the only popular software in existence that uses this mode. IGE is avoided by all modern cryptographers because the authentication is broken, however Telegram uses this mode but not the authentication. There's no particular justification for this decision over just using an AES mode that everyone uses, but there's a lot of potential pitfalls if not done carefully. When you ask what type of authenticated encryption scheme Telegram uses, their answer is "none of them". Normally this would be a huge problem. However, they have solved this with their own custom "security checks". These are also not "well known" because Telegram invented them. When you ask what type of PKCS they use for padding, the answer is "we came up with our own padding algorithm". This was not "well known" because Telegram invented it. The padding issue they fixed in v2, since it turned out to introduce a vulnerability, but I assume you get what I mean by this point. Contrast this with Signal, which is also ultimately a unique protocol but is one that was implemented using robust, tested primitives in recommended combinations with boring standard choices for all of the details.