This blog is reserved for more serious things, and ordinarily I wouldn’t spend time on questions like the above. But much as I’d like to spend my time writing about exciting topics, som…

Blog post by crypto professor Matthew Green, discussing what Telegram does (I wasn’t familiar with it) and criticizing its cryptography. He says Telegram by default is not end-to-end encrypted. It does have an end-to-end “secret chat” feature, but it’s a nuisance to activate and only works for two-person chats (not groups) where both people are online when the chat starts.

It still isn’t clear to me why Telegram’s founder was arrested. Green expresses some concern over that but doesn’t give any details that weren’t in the headlines.

  • @[email protected]
    73•4 months ago

    I mean really, we don’t need an entire article to explain how encryption works on Telegram.

    1. Chats by default aren’t fully e2e. Your key must be kept on the server(s) to enable instant sync with other devices

    2. There is a full e2e chat, you can enable this at any time. But, it doesn’t do groups, it’s only between 2 parties, and it doesn’t sync across devices.

    3. Telegram’s encryption isn’t open source, so no one can verify it’s soundness or risks.

    None of this is new info, it’s been talked about for 2 years now.

    • @pivot_root
      13•4 months ago

      We really don’t need more than #3 for a reason to stay far away from Telegram. Security through obscurity is not security, and neither is rolling your own crypto.

      • @[email protected]
        3•4 months ago

        Just note that the comment was inaccurate, in that their weird encryption is indeed open source at least.

    • poVoq
      10•4 months ago

      Telegram’s encryption isn’t open source, so no one can verify it’s soundness or risks.

      This is not true, it is available in the open-source Telegram clients.

      What you probably mean is that it is using an unusual and not well studied encryption algorithm. This means you need to be a real cryptography expert to spot flaws in it.

      Telegram justifies this with a bit of FUD about well known encryption algorithm being NSA sponsored etc, but when cryptography experts did look at Telegram’s homegrown algorithm they were less than impressed.

    • @solrizeOP
      7•4 months ago

      Sure, I just have never used telegram or paid attention to it until that guy got arrested. So the quick overview by a cryptographer was helpful.

    • @[email protected]English
      1•4 months ago

      Are there any programs that can do e2e in a group chat? My limited knowledge of e2e and encryption makes me think that’d be extremely difficult and even clunkier

      • @[email protected]English
        4•4 months ago

        Element (really any Matrix client that supports e2ee) but rooms with hundreds I’d people and having encryption enabled is going to to have lots of messages with key exchange errors.

      • @solrizeOP
        2•4 months ago

        Group chat is a tricky problem and the modern crypto group (moderncrypto.org) talked about it at great length a few years back. I don’t know whether any software exists that incorporates all those ideas, but that’s mostly because I haven’t really been looking for it.

        • poVoq
          2•4 months ago

          There is the MLS standard now that was explicitly developed with e2ee group chat applications in mind. From what I have read so far, this new standard seems well regarded by cryptography experts.

      • Daemon Silverstein
        1•4 months ago

        PGP/GPG encryption. It works with any IM, social network, anything (at least if the platform/program/app/medium allows for sufficiently lengthy messages so to carry the encrypted payload). There are some IMs that bring PGP/GPG natively, as well as extensions for existing IMs that also adds PGP/GPG feature, but PGP/GPG doesn’t need to be native to the app to convey encrypted messages, it’s a base64 text. It’s really an E2EE.

      • Em Adespoton
        0•4 months ago

        Messages app by Apple. Not extremely difficult, but has its trade offs, and easier when all devices share a CA.

            • ᗪᗩᗰᑎ
              1•4 months ago

              Doesn’t the concept of using a CA (which are generally also central authorities) go against the idea of E2EE that only required to (or more) endpoints or am I missing something? Signal group messages (and the protocol/concept behind it) work without a CA. I think I’m missing something, can you connect the dots for me?

              • Em Adespoton
                2•4 months ago

                The CA is purely a way to provide validation that the endpoints being connected are who they say they are; the actual signing certificates are still private. Apple uses a central directory; Signal depends on certificates linked to one way hashes of phone numbers.