I experienced this too, Facebook will block most torrent links, regardless of if they're legal or not. I've taken to encoding these with Base64 first and instructing the recipient to decode them.
This was just a quick fix, but I agree with you on the e2e messaging service. However, I do wish more e2e services like Telegram would open source their backend. Looks like Signal does now at least!
When a secret chat is created, the participating devices exchange encryption keys using the so-called Diffie-Hellman key exchange. After the secure end-to-end connection has been established, we generate a picture that visualizes the encryption key for your chat. You can then compare this image with the one your friend has — if the two images are the same, you can be sure that the secret chat is secure, and no man-in-the-middle attack can succeed.
Newer versions of Telegram apps will show a larger picture along with a textual representation of the key (this is not the key itself, of course!) when both participants are using an updated app.
Always compare visualizations using a channel that is known to be secure — it's safest if you do this in person, in an offline meeting with the conversation partner.
Q: Why not just make all chats ‘secret’?
All Telegram messages are always securely encrypted. Messages in Secret Chats use client-client encryption, while Cloud Chats use client-server/server-client encryption and are stored encrypted in the Telegram Cloud (more here). This enables your cloud messages to be both secure and immediately accessible from any of your devices – even if you lose your device altogether.
The problem of restoring access to your chat history on a newly connected device (e.g. when you lose your phone) does not have an elegant solution in the end-to-end encryption paradigm. At the same time, reliable backups are an essential feature for any mass-market messenger. To solve this problem, some applications (like Whatsapp and Viber) allow decryptable backups that put their users' privacy at risk – even if they do not enable backups themselves. Other apps ignore the need for backups altogether and fade into oblivion before ever reaching a million users.
We opted for a third approach by offering two distinct types of chats. Telegram disables default system backups and provides all users with an integrated security-focused backup solution in the form of Cloud Chats. Meanwhile, the separate entity of Secret Chats gives you full control over the data you do not want to be stored.
This allows Telegram to be widely adopted in broad circles, not just by activists and dissidents, so that the simple fact of using Telegram does not mark users as targets for heightened surveillance in certain countries. We are convinced that the separation of conversations into Cloud and Secret chats represents the most secure solution currently possible for a massively popular messaging application.
I imagine it is quite easy to reassemble a broken link with some extra whitespace or random characters (unless you really scramble it which makes the process of manually "decoding" tedious). At that point you might as well automate the process and use base64
