> 2. A passing look at the docs would reveal that we do not use IGE that way, and instead use SHA1 for integrity check (see 'message key' here: https://core.telegram.org/mtproto/description). The problems you mentioned as endemic to IGE used for integrity verification, are therefore irrelevant in this case.
The consensus seems to be that you're doing encrypt-and-mac, where the mac is just a sha1? If that's true, then you're relying on broken properties of IGE (not provably UF-CMA), and your protocol does not provide provable integrity. That's an essential part of any secure protocol.
> As for KDF, going for slower provable algorithms used for each incoming\outgoing packet may be a preferred solution for projects aimed at the relatively small security crowd. But we don't really compete in this area, our competition is WhatsApp and other mass market messengers.
That's interesting, because the thing you've made up is actually slower than a provably secure KDF.
> 2. And what problems with IGE are you aware of? Any known attack? As far as we know, it is the ubiquitous CBC that has had issues. And by the way, Kerberos had to abandon PCBC - not IGE.
IGE was the first attempt at an "authenticating encryption mode," originally for Kerberos. It was a failed attempt (it does not provide integrity protection), and had to be removed. That was the beginning of a 20 year quest for an authenticating encryption mode that works, which recently culminated in modes like OCB and GCM. I don't see any integrity protection documented anywhere in your protocol spec, so if you're relying on IGE, it's broken.
What's more, any "problems" with CBC (I assume you're referring to padding oracle attacks) are not specific to CBC, and are endemic to IGE as well.
> The team behind Telegram, led by Nikolai Durov, consists of six ACM champions, half of them Ph.Ds in math. It took them about two years to roll out the current version of MTProto. Names and degrees may indeed not mean as much in some fields as they do in others, but this protocol is the result of thougtful and prolonged work of professionals.
I don't think their academic credentials or the amount of time they spent on this are the important metrics. If you're trying to suggest that they're thoughtful, the best metric for demonstrating that would be something like a proof for the (honestly naive-looking) KDF they made up.
In essence, the protocol seems to reflect many choices that anyone familiar with the field can immediately identify as suggesting a lack of understanding. It could be that these are simply brilliant moves that we non-ACM champions are too primitive to understand, but if that's true, you need to justify them with proofs in order to support them. Otherwise we're going to interpret them for how they appear.
> Thank you for the offer to join in the project you represent. However, we feel that what we are doing is going in a somewhat different direction and has its own potential.
Could you describe how your projects objectives are inconsistent with a protocol ratchet like Axolotol or the full TextSecure protocol?
The reason that cryptographers laugh at people who advertise "military grade cryptography" or "we use AES256" is because the choice of crypto primitives is often less important than how they're composed. Those phrases tend to reflect a critical misunderstanding of that, and often mean that a project is using secure primitives in a way that completely undermines their security.
At a glance, while this project is using secure (if aging) primitives, they've made some extremely unusual protocol choices that they need to publicly justify rather than simply describing in an API doc. Just at a glance, the use of modes like Infinite Garble Extension (a failed mode for Kerberos) is troubling, they made up their own KDF (with no proof), and they make what appear to be some amateur mistakes with how they use RSA.
If Telegram folks are on this thread, I'd encourage you to take a look at the TextSecure protocol. If you think it's interesting, you can federate into our network, get a provably secure asynchronous forward secrecy protocol, and also have access to an existing 10MM user base.
The consensus seems to be that you're doing encrypt-and-mac, where the mac is just a sha1? If that's true, then you're relying on broken properties of IGE (not provably UF-CMA), and your protocol does not provide provable integrity. That's an essential part of any secure protocol.
> As for KDF, going for slower provable algorithms used for each incoming\outgoing packet may be a preferred solution for projects aimed at the relatively small security crowd. But we don't really compete in this area, our competition is WhatsApp and other mass market messengers.
That's interesting, because the thing you've made up is actually slower than a provably secure KDF.