Telegram routinely boasts about their secured messaging available for truly private conversations between two parties using their app. However, default chats in Telegram are only encrypted server-to-client, not client-to-client, which means you have to be a little proactive in making sure your private conversations on Telegram are really private.
This is, in my opinion, one of Telegram's downfalls when compared to other security-minded messaging platforms such as Signal Private Messenger which use the already established Signal Protocol for end-to-end encryption without any manual work by its users. Even WhatsApp, which Telegram claims is less secure than its own service, adopted the Signal Protocol for messaging in 2016. These chats are only stored on the devices of its users, not on their servers.
Telegram uses a proprietary encryption protocol, MTProto, which still has to prove itself. By default, Telegram's normal cloud-based chats are stored on their servers. This is why it's important to use their client-to-client encryption option over their default server-to-client encryption — so messages remain on user devices only, not on company servers that could potentially be subpoenaed for information.
So how do you make sure you're using end-to-end encryption in your chats on Telegram? Just use Telegram's "Secret Chat" feature. The benefits of using Secret Chat over a regular chat are numerous.
- Messages use end-to-end encryption.
- Messages stay on devices, not in Telegram's servers.
- Messages are device-specific, so you can not sync them with other devices.
- Messages cannot be forwarded.
- Messages can be set to self-destruct.
- Messages can only be deleted for both parties, not one or the other.
To start a Secret Chat on an iPhone, tap on the new message icon in the top right of the Chats tab, then select "New Secret Chat." Select the contact you'd like to initiate the Secret Chat with, and on the next screen, it will show that you have invited them to join. Note that they need to be in your contacts list in order to Secret Chat with them.
To start a Secret Chat on an Android phone, tap on the new message icon in the bottom right of the Chats screen, then select "New Secret Chat." Select the contact you'd like to initiate the Secret Chat with, and on the next screen, it will show that you have invited them to join. Note that they need to be in your contacts list in order to Secret Chat with them.
In a Secret Chat, you can send photos, videos, voice messages, stickers, files, and even your location. Just be aware that photos, videos, and other files are stored on Telegram's servers, but they are encrypted with a different key not known to the server so they remain indecipherable outside of you or your recipient's phone.
You can also initiate an end-to-end encrypted phone call, though, all phone calls in Telegram use end-to-end encryption. The phone call log will end up outside of the Secret Chat, however odd that sounds.
As stated above in the bullet list, if you decide to delete a message in a Secret Chat, you can only do so for both you and the other party. You can do this in regular chats as well, but you also have the option to just delete the message for yourself.
Additionally, you can "clear" the history for a Secret Chat to erase all messages within on both sides. If someone decides to "delete" the whole Secret Chat, the other party will still be able to view all of the messages on their side. However, iPhone users will get a "Delete and Exit" notification to prompt them to clean house, while Android users will just get a "Secret chat canceled" alert, and it will be up to them to manually delete it.
If you enable screenshots in Telegram on Android, any time you take a screenshot in a Secret Chat, an alert will appear directly inside the Secret Chat with them. If you take a screenshot on an iPhone, only the other person will get a notification in the Secret Chat.
And a few quick last things to note: You cannot convert regular chats to Secret Chats, nor can you downgrade Secret Chats to regular chats, and Secret Chats do not support group messaging — only person to person.