Comment on Federated End-to-End Encrypted Messaging is Coming Soon

• iltg@sh.itjust.works ⁨2⁩ ⁨months⁩ ago

  hi! sorry for throwing this here without explaining much, explaining a bit seems definitely due diligence!

  so, i need to make some things clear, skip if you know these already:

  fediverse

  the fediverse is not a single software, rather a collection of softwares speaking a common language (sharing a protocol: activitypub). the classic example is mail: on gmail you can email folks on outlook. they just know how to send messages to other instances/servers/deployments, and how to receive. for example, email (SMTP) expects data formatted in a certain manner (lots of headers and a body, kinda) on port 25. Activitypub expects activities (json-ld documents) coming over inboxes (POST to http endpoints).

  compatibility

  now, say emissary sends an encrypted message to a mastodon user. mastodon doesn’t know what to do with that document! it’s a garbled mess of encrypted data, what is mastodon supposed to do with it? there are no rules for this in the spec! the post claims “federated” (aka, across multiple servers) e2ee messaging, and that already exists with multiple solutions. what they mean to me is either

  • they are making a new e2ee chat: great! emissary users will get a way to message other emissary users. but that’s it: you need to be on emissary, like with matrix you need to be on matrix
  • they are making a fediverse e2ee chat: this isn’t easy! you can’t just make it for yourself, you need to clearly define how it works, and everyone must implement it too. otherwise mastodon or lemmy won’t know what to do with the message you sent

  spec

  they link two specs: MLS (an IETF spec defining scalable e2ee messaging), and activitypub-e2ee. the first one is great: i think matrix wants to move their encryption to that? it’s good, but it’s a spec: you need to adapt it to your use. the second one is how MLS can be applied to Activitypub communication: the thing we care about! unfortunately the later spec is just a draft, so it needs more work and it’s unlikely that it will see adoption in this state.

  asymmetric encryption

  so now i need to go a bit into asymmetric encryption, in this case RSA. there’s a lot of great examples if you put “asymmetric encryption” or “rsa” into google, but i’ll try my best here. imagine 2 folks trying to communicate, Alice and Bob, but they need to have a postperson deliver their messages. they don’t want such postperson reading them! how to do that? A and B both get two “keys”: one private and one public. these keys are related to each other: a pubkey “has” a privkey, and vice versa. these keys are also “magic” (math, good luck if u wanna dig in here, if you’re not into math just trust me the keys are magic). using a public key, you can encrypt a message so that only the related private key can decrypt it. and using a private key you can encrypt a message so that only its public key can decrypt it. the second case is for identity proofing, we care about the first one: if A and B make their public keys public (heh), they can both use such keys to create messages meant only for either A or B, assuming they still hold their private keys, and nobody else. because math magic

  activitypub keys

  in activitypub every actor holds a private and public key. this is how the protocol does “authorized fetch”, meaning making sure an activity truly comes from the actor claiming to send it. so we can use these keys for doing e2ee!

  Alice <—> A’s server <—> B’s server <—> Bob

  Alice can ask her server to get Bob’s public key from Bob’s server, and then encrypt a message for Bob and send it via the servers without anyone snooping in. Great? NO!

  • A’s server can lie about bob’s key, give a random key, decrypt the message, then encrypt it with bob’s real pubkey and send it. this way bob knows nothing and A’s server can read the message. Same way, A’s server can give bob a fake pubkey for alice, so read the message and then encrypt and re-send to alice with her real key. So trust is broken! the spec offers 3 solutions to this:
  • trusting your server, which is kind of the starting point and we don’t want that
  • having a third party validate keys (either a centralized solution which Alice and Bob ask, or some yet-to-invent federated way to handle keys. we’re kinda back at point one)
  • having alice and bob exchange keys themselves (maybe send them on matrix or signal, delegating the “identify and trust” issue to those services)

  “knowing irl”

  some users compared the issue with “knowing each other irl” but it’s not the same. on signal, i trust you to be you, and our conversation to be private. if i search you by username, i can just message you. trusting your username is you is a meaningless discourse here: you are your username. i’m writing this to “Abundance114”, i don’t care who you are, i just want this to reach “Abundance114”. so on signal i plug your user and our keys automagically reach each other safely. this spec doesn’t explain how this happen: i would need to first identify and trust you, Abundance114, and then find a way to safely communicate with you so we can exchange keys.

  ---

  i hope this wan in-depth enough! i’m not an encryption expert, if any is here i’m open to critics, but this seems reasonable to me with my protocol and encryption experience. basically i believe this post is hype bait: whatsapp is e2ee, but who has the keys? do you trust meta? sure, the message travels encrypted, but who can read it? only you? an e2ee system is not just its encryption tech, but the way keys are securely shared

  source

  • TheProtagonist@lemmy.world ⁨2⁩ ⁨months⁩ ago

    What would be the main difference compared to Matrix, which also claims to be “an open network for secure, decentralised communication”?

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    • iltg@sh.itjust.works ⁨2⁩ ⁨months⁩ ago

      nothing per se, depends on implementation

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  • Yliaster@lemmy.world ⁨2⁩ ⁨months⁩ ago

    My primary concern was that last bit you wrote: e2ee doesn’t necessarily guarantee anything; corporate overlords like Meta has abused it and iirc the British government is starting to fuck with e2ee too.

    Does e2ee even mean anything anymore?

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    • iltg@sh.itjust.works ⁨2⁩ ⁨months⁩ ago

      TLDR: an e2ee channel means “everything passing over this channel is super secure and private, but it needs some keys for this to work”. e2ee means something: you can not care about most issues with delivery and protection and such, but you need to care about the keys. if you don’t do that, you are probably ruining the security of such e2ee channel

      ---

      end-to-end-encryption solves one issue: transport over untrusted middleware, doesn’t mean much by itself. it’s being flung around a lot because without proper understanding sounds secure and private.

      it’s like saying that i ship you something valuable with a super strong and impenetrable safe. but what do i do with the key? e2ee is the safe, solves the “how can i send you something confidential when i dont trust those who deliver it”, and it means much! it’s a great way to do it.

      but it solves one problem giving a new one: what to do with the key? this usually can be combined with other technologies, such as asymmetric encryption (e.g. RSA), which allows having keys which can be publicly shared without compromising anything. so i send you an impenetrable code-protected safe with an encrypted code attached, and only your privkey can decrypt the code since i used your pubkey!

      (note: RSA is used for small data since encryption/decryption is cpu intensive. usually what happens is that you share an AES key encrypted with RSA, and the payload is encrypted using that AES key. AES is symmetric: one key encrypts and decrypts, but AES keys are small. another piece of technology attached to make this system work!)

      but now comes the user-friendliness issue: very few are big enough nerds to handle their keys. hell, most folks don’t even want to handle their passwords! so services like matrix offer to hold your keys on the server, encrypted with another passphrase, so that you don’t need to bother doing that, just remember 2 passwords or do the emoji compare stuff. it’s meh: compromising the server could allow getting your keys and kinda spoils e2ee, but it’s convenient and reasonably secure.

      what does whatsapp do? i don’t know! but it kind of magically works. if they do e2ee, where are the keys??? how does meta handle reports if messages are e2ee???

      also, e2ee works if you can trust the key you’re sending to! as mentioned in the ‘activitypub keys’ section before, if you ask a middleman the key for your recipient, can you trust that’s the real key? e2ee doesn’t cover that, it’s not in its scope

      so what does e2ee mean? it means: super strong channel, ASSUMING keys are safe and trusted. e2ee as a technology doesn’t solve “all privacy” or guarantee that nobody snoops in per se. it offers a super safe channel protected by keys, and lets you handle those keys how you more see fit. which meaning deciding who you trust to send, how you let others know how to encrypt for you (aka share your pubkey) and how you will keep your privkey safe.

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