I have been working on an Android App quite a while now, starting from a simple idea.

A messenger where messages travel directly between phones with no servers in between. Using direct WebRTC encrypted connections (SRTP/DTLS), there are no servers that stores, reads, or relays content. Group chats use a gossip protocol where members relay to other members.

The only infrastructure the app touches is a signalling relay to set up the connection (no message content), a push notification to wake up a sleeping phone (also no content), and a TURN relay for restricted networks (encrypted packets only).

I wrote a detailed white paper explaining the full architecture: https://www.mindtheclub.com/white-paper.html

The app is in Open Testing on Google Play (1,000 tester cap): https://www.mindtheclub.com/beta-signup.html

I’m interested in this community’s perspective on whether the architecture holds up.

  • Arthur Besse@lemmy.mlEnglish
    1·
    3 days ago

    wait a minute… i asked this:

    assuming a compromised/compelled google and/or cloudflare, is it possible to mitm people?

    and you replied this:

    About MITM under a compromised provider, both peers verify each other’s public key independently after one QR scan. The scanner gets the other party’s fingerprint from the QR, the scanned party gets the scanner’s fingerprint sealed inside the contact request, encrypted to a key the scanner has already verified. A compromised directory cannot substitute either key without producing a fingerprint mismatch on one side or a failed decryption on the other, and it doesnt hold the private material to do either. The mechanism is now documented in “How MTC Connects You”.

    in my first reply here i said that “that sounds reasonable” but now i looked a little closer. you say this is “now documented” but you actually also mean now implemented, don’t you?

    I just looked at github and i see that until this commit one hour ago (four hours after i asked) you were actually calling db.collection("users").document(peer.userId).get() to read a publicKey from Firebase. This is my first and last glance at your github for the time being; I’m going to stop reviewing your project for now because the design is fundamentally changing while we’re talking, and not in a transparent way. i shouldn’t need to find out from git that your answer to my question is the result of a change you just made after i asked the question.

    I’m also going to share here what i wrote to you privately about why i still don’t want you to post this to !cryptography@lemmy.ml, even now that you’ve removed the claim about not having single points of failure:

    i [still] don’t want you to post it to /c/cryptography in its current state. the website is not saying “this is unreviewed cryptography, do not rely on it for anything serious” but on the contrary it says “Why Choose MindTheClub?”, “Uncompromised Security”, “Total Privacy”, “Unbreakable Encryption”, “Privacy Without Compromise”, etc. you’ve written the marketing copy to encourage regular users to rely on your software before having independent review of it; this is backwards.

    if your website didn’t say all of those things and you were asking for review of your design and/or source code without simultaneously telling the general public that your “very new” software already provides “Total Privacy”, it would be a good post for /c/cryptography and other places.

    HTH.

    • GradleSurvivor@lemmy.mlOPEnglish
      1·
      2 days ago

      Hello,

      Sorry to bother you again. I just wanted to share some architectural changes I’ve made recently.

      I’m taking advantage of the fact that you’re the only one who has given me valuable feedback so far, so please feel free to ignore this message if you judge it’s not worth your time.

      Along with moving the public key away from Firebase (the MITM issue), and implementing the sealed sender feature (sender information encrypted before it reaches Cloudflare), I’ve added a TOR service that the sender uses to connect to Cloudflare, both for the wake-up (instructing Cloudflare to send the FCM message via Firebase) and for signalling. I think this strengthens the “sealed sender” property.

      I don’t think I can avoid cloud services entirely, except when the two peers are within Bluetooth range, I have that feature too. But I believe the sealed sender design limits metadata leakage in a reasonable way. My understanding is that Signal does something similar.

      I’m now focused on defining a solid architecture rather than working on my landing page, which, as I appreciate, was initially built with a marketing mindset. So, I’m now more interested in technical feedback. I’ll get to the landing page later, once things have settled.

      The App is not for sale anyway at the moment, if and when I will eventually try to sell it, I was thinking about a monthly subscription, that would cover the cloud services costs plus some revenue.

      • Arthur Besse@lemmy.mlEnglish
        1·
        1 day ago

        i won’t comment on your tor-to-cloudflare-to-google design because i haven’t looked at it and don’t expect i’ll make time to anytime soon.

        I don’t think I can avoid cloud services entirely

        Lots of similar things are able to avoid cloud services entirely; your perceived need to use them is driven by your so-called “server-free” design which isn’t really free of servers at all because, as the saying goes, “there is no cloud, just other people’s computers”.

        You could also use Google’s push notifications but make them optional, btw. Making the protocol have a hard dependency on that is a choice you are making.

        when the two peers are within Bluetooth range

        having users’ devices transmit fixed identifiers while moving around is terrible for privacy / great for surveillance, and firmly in the category of things which i not only do not recommend but implore people to not build. please don’t.

        I’m now focused on defining a solid architecture rather than working on my landing page

        But your landing page is still up, and still making unsubstantiated claims and encouraging users to trust in (aka rely on) a thing which is totally half baked. You are still peddling snake oil. You should fix that.

        The App is not for sale anyway at the moment, if and when I will eventually try to sell it, I was thinking about a monthly subscription, that would cover the cloud services costs plus some revenue.

        I see, now we’re getting down to it :)

        A few questions on that front:

        1. Did you disclose to your beta users (and the general public you’re asking for help here from) that they/we are doing volunteer work for what you intend to be a for-profit endeavor?
        2. How do you plan to limit access to your cloud services so only subscribers can use them?
        3. If someone wants to fork the software (assuming you’re planning to keep it under a free software license) presumably users of the fork will not be able to communicate with the users who are paying you, since the whole thing fundamentally requires the cloud infra you’re paying for? Or, if you actually want forks to be interoperable, how do you expect that to work?
        • GradleSurvivor@lemmy.mlOPEnglish
          1·
          14 hours ago

          About cloud services: The core idea behind the “server-free” design is to keep users’ messages from ever touching the cloud. Wake-up notifications and signalling (metadata) do require some kind of cloud service before the peer-to-peer connection is established. The only way to avoid third-party cloud services entirely would be to build your own, though I’m not sure that would really change how the dependency is perceived from a client’s perspective.

          About Bluetooth: Messages are still end-to-end encrypted, anyway It’s a user choice, you don’t have to use it, and I found a lot of people appreciate this feature, Briar has it.

          About the landing page: At least I’m clear I’m still in beta, evolving situation, anyway I’m working on the right wording.

          About the questions:

          1. Did you disclose to your beta users… I did in my “learn more about Open Testing”, but again, I’m going to change the text to be more explicit.
          2. How do you plan to limit access… Beta testers get it free forever, no gating needed for them. Only post-launch signups will need a subscription, and that gating (a server-side check on the Play purchase token) is planned, not built yet.
          3. If someone wants to fork… That is right, a fork on its own backend can’t talk to my users, because both sides need to use the same signalling infrastructure to find each other. Separate forks aren’t interoperable by default.
          • Arthur Besse@lemmy.mlEnglish
            1·
            12 hours ago

            The core idea behind the “server-free” design is to keep users’ messages from ever touching the cloud

            "but why" meme, with the the text "but why?" over an image of Ryan Reynolds in medical scrubs in the film Harold & Kumar Go To White Castle

            given that the messages are encrypted, what is the advantage that you perceive in using “the cloud” (servers) only for signaling rather than transmitting the actual ciphertext through them? Wouldn’t your “cloud” servers see “just the metadata” either way?

            It saves some costs for you, but it comes at the cost of requiring users to be online at the same time to exchange messages… is there some other advantage that you see?

            a server-side check on the Play purchase token

            ah, so it will be the kind of “free open source software” which can only be used via Google Play 🙄

            Separate forks aren’t interoperable

            that’s another thing you should inform potential users of explicitly, if you want to be honest.

    • GradleSurvivor@lemmy.mlOPEnglish
      2·
      3 days ago

      Yep, true. As I said, the conversation we had today was very helpful for me to understand and work on some stuff, and I will continue to work on it. There is another couple of observations I would like to think about. So genuinely, thank you for your time and feedback, of course I respect the decision, not going to re-post.

      • Arthur Besse@lemmy.mlEnglish
        1·
        1 day ago

        you say this is “now documented” but you actually also mean now implemented, don’t you?

        I just looked at github and i see that until this commit one hour ago (four hours after i asked) you were actually calling db.collection(“users”).document(peer.userId).get() to read a publicKey from Firebase

        Yep, true

        thank you for your (belated) honesty on this :)

        So genuinely, thank you for your time and feedback, of course I respect the decision, not going to re-post

        thank you and you’re welcome