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e3x: mention future/forward secrecy, add comparison with OTR, Axolotl? #117

Open ariddell opened 9 years ago

ariddell commented 9 years ago

Would it be useful to just state how e3x is similar/different from the future/forward secret approaches of OTR and the Axolotl ratchet? I know there's a list of links, but I'll admit I'm not sure how e3x fits into the universe that Marlinspike describes here: https://whispersystems.org/blog/advanced-ratcheting/

dvanduzer commented 9 years ago

You get forward secrecy because a handshake uses ephemeral keys to generate the session key for an exchange. The notion of "future secrecy" isn't really clear to me. Moxie brings it up to illustrate problems with deriving new session keys from previous session keys, which e3x doesn't do.

Ratcheting makes sense in store-and-forward messaging, but e3x is about real time communication between two endpoints.

ariddell commented 9 years ago

Ok, I think I got it. You're sending streams between peers so there's no chance to generate a new key as one would with OTR. Is that right?

quartzjer commented 9 years ago

You can generate new ephemeral keys and send new handshakes, but they have no coupling or relationship with previous ones, they just have to be "newer" (have a higher sequence).

If you generate a new hashname though, you'll need an app-level mechanism to re-register or re-associate trust at a higher level.

A better comparison table/breakdown would be great and should eventually happen, on my radar first though is just getting some better api/docs/examples out to help make v3 more immediately usable :)

quartzjer commented 9 years ago

@ariddell do you have any examples of tables and/or lists of columns you'd like here? Happy to convert the list to a table soon.

ariddell commented 9 years ago

I'm working on this. I'd definitely like to see PFS and deniability among the features one is comparing. I still need to understand better this idea of "future secrecy".

ariddell commented 9 years ago

(just for my own reference, I'm thinking about the "Comparison" section at https://github.com/telehash/telehash.org/blob/master/v3/e3x/README.md)

Another one to include could be ntor (spec).