How does the Diffe-Hellman key exchange happen? How do you know that Telegram is not secretly intercepting the keys? Based on the FAQ, it looks like they are us

How does the Diffe-Hellman key exchange happen? How do you know that Telegram is not secretly intercepting the keys? Based on the FAQ, it looks like they are using some form of RSA public/private keys. Does each user have their own set of keys signed by a CA? Has the source code been vetted on both client and server side to ensure that the encryption is happening properly? There are a lot of problems with just saying "it's encrypted."