Telegram once touted as the WhatsApp killer, is a messenger with a focus on security and privacy. It claims its aim to be to create a truly free messenger, without any ads and with privacy and data security.
While Telegram have stuck to their word, even though they are valued at $5 billion, they have refused to sell out or place ads to make money.
They have also resisted authorities’ attempts at forcing them to loosen their encryption for them and have relocated their headquarters several times due to that.
How does Telegram secure its data?
Telegram promises security by providing end-to-end encryption on its messenger platform and it uses a custom developed protocol named MTProto Mobile Protocol to do so. According to Telegram’s FAQs, MTProto allows them to achieve reliability on weak mobile connections as well as when delivering large files (e.g. Photos, videos, etc.).
There is a more to it but ins short MTProto combines three feature
a) A mode of operation known as Infinite Garble Extension (IGE);
b) A short-term key derivation mechanism;
c) And integrity check on the plaintext.
However, when it comes to cryptography, the first rule is “Do not Roll Your Own Crypto“. And the second rule is “DO NOT ROLL YOUR OWN CRYPTO”.
As explained in this thread on StackExchange, the issue with an “Own Cryptography” is that you have to rely on your own intelligence, vs, in case of a standardised Cypto, intelligence of several experts in the field.
That’s not to say that MTProto is completely junk, but the aspersions start casting henceforth.
So how secure is Telegram really?
As I mentioned earlier, it’s not that Telegram’s security suffers due to usage of a custom cryptography method, as eveidenced by the fact that they have been chased out of at least 3 countries who wanted to force them to decrypt the chats, including Russia.
However, as this 2015 paper suggested, MTProto is not
The author of the research paper elaborated on two attacks, first using a Padding-Length Extension, the other with Last Block Substitution, both though were patchable vulnerabilities.
And it comes down to that really, the two sides, the side who is trying to keep secrets, and the side that is trying to expose them will constantly be at loggerheads. And it’s upto the side trying to maintain privacy to stay a step ahead.