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BRIAN_____'s profile
Brian Smith
Brian Smith
Brian Smith
@BRIAN_____

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Brian Smith

@BRIAN_____

Code farmer. Security, crypto, performance, networking, usability. Rust, C++, C, Haskell, DSLs, etc. *ring*, webpki, crypto-bench, mozilla::pkix.

Honolulu & San Francisco
briansmith.org
Joined April 2008

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    1. Matthew Green‏ @matthew_d_green Nov 16
      Replying to @tqbf @kennwhite @stevecheckoway

      There were half-baked proposals to have clients detect repeated DH public keys and barf.

      2 replies 0 retweets 3 likes
    2. Thomas H. Ptacek‏ @tqbf Nov 16
      Replying to @matthew_d_green @kennwhite @stevecheckoway

      Those are from TLS 1.3 people who are deliberately breaking compat to break the enterprise monitoring use case, right?

      2 replies 0 retweets 1 like
    3. Brian Smith‏ @BRIAN_____ Nov 16
      Replying to @tqbf @matthew_d_green and

      ServerHello.Random could be the ECDH private key, encrypted w/ shared secret, and everything would work fine for both use cases, for typical ECDH key sizes. And/or one could build a similar thing directly on top of the "randomness improvement" draft mechanism w/ a random Random.

      1 reply 1 retweet 0 likes
    4. Brian Smith‏ @BRIAN_____ Nov 16
      Replying to @BRIAN_____ @tqbf and

      That's just 2 minutes of thinking. No doubt there are "better" ones. Seems unrealistic to expect to prevent the server from leaking the ECDH key to something it trusts, in a scalable way that depends only on out-of-band shared key + the bytes on the wire. What's the exact goal?

      1 reply 0 retweets 0 likes
    5. Stephen Checkoway‏ @stevecheckoway Nov 16
      Replying to @BRIAN_____ @tqbf and

      Goal for whom? Enterprises: decrypt data by man-on-the-side boxes. TLS WG: prevent exactly that. Matt: provide a visible, standardized mechanism to do it so enterprises don’t do exactly the sort of thing you propose.

      1 reply 0 retweets 0 likes
    6. Brian Smith‏ @BRIAN_____ Nov 16
      Replying to @stevecheckoway @tqbf and

      The "prevent exactly that" group. I get the impression they're less interested in preventing "enterprise" stuff and more interested in preventing government-scale use of that stuff. There's lots of reasons one can't prevent, technologically, the "enterprise" use cases.

      1 reply 0 retweets 2 likes
    7. Matthew Green‏ @matthew_d_green Nov 16
      Replying to @BRIAN_____ @stevecheckoway and

      Once enterprise builds the systems and gets their revisions into every Blue Coat middlebox, half the engineering work of those abusive governments is done.

      2 replies 0 retweets 0 likes
    8. Brian Smith‏ @BRIAN_____ Nov 16
      Replying to @matthew_d_green @stevecheckoway and

      Yeah, that's what I'm trying to say. And, to be honest, the design & implementation of even an impossible-to-detect mechanism is not hard.

      1 reply 0 retweets 0 likes
    9. Kenn White‏Verified account @kennwhite Nov 16
      Replying to @BRIAN_____ @matthew_d_green and

      how do you get around the CA problem? I'd think a stealth intermediary would get flagged pretty quickly by Mountain View.

      1 reply 0 retweets 0 likes
    10. Brian Smith‏ @BRIAN_____ Nov 16
      Replying to @kennwhite @matthew_d_green and

      Like I mentioned earlier in this thread, if you want to share a static key but you need the ECDH key to change every connection, you can do that by making the ECDH key a function of the static key and Server.Random.

      1 reply 0 retweets 3 likes
      Brian Smith‏ @BRIAN_____ Nov 16
      Replying to @BRIAN_____ @kennwhite and

      If we wanted to prevent this kind of thing, then we would have tried to find a way to make the protocol secure by making Server.Random deterministic, and get people to insist on that variant of TLS. (Even now, given the use of ephemeral DH, does Server.Random need to be random?)

      12:53 PM - 16 Nov 2018
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Matthew Green‏ @matthew_d_green Nov 16
          Replying to @BRIAN_____ @kennwhite and

          This is an impossible problem. You’d have to lock down every potentially random byte of the protocol to make this work, and even then you could always use a timestamp or an out-of-band channel.

          1 reply 0 retweets 0 likes
        3. Brian Smith‏ @BRIAN_____ Nov 16
          Replying to @matthew_d_green @kennwhite and

          It would be difficult. I think it helps that there are few unencrypted extensions in TLS 1.3 and almost all data is encrypted/authenticated. On the other hand, the record header is authenticated but not (required to be) verified to be in range so it allows a covert channel.

          1 reply 0 retweets 0 likes
        4. Brian Smith‏ @BRIAN_____ Nov 16
          Replying to @BRIAN_____ @matthew_d_green and

          (FWIW I argued against the record header covert channel on the TLS WG mailing list but people disagreed.) I agree that such a design would be tricky and would require a lot of effort (not just a couple of tweets) and kind of too late since TLS 1.3 shipped. Not sure *impossible*.

          1 reply 0 retweets 0 likes
        5. Brian Smith‏ @BRIAN_____ Nov 16
          Replying to @BRIAN_____ @matthew_d_green and

          Oh, maybe it can be done for QUIC.

          1 reply 0 retweets 1 like
        6. Subodh Iyengar‏ @__subodh Nov 16
          Replying to @BRIAN_____ @matthew_d_green and

          Quic packets are the record layer for quic, so quic only forwards tls messages not records

          1 reply 0 retweets 1 like
        7. Brian Smith‏ @BRIAN_____ Nov 16
          Replying to @__subodh @matthew_d_green and

          Yeah, I mean, more generally, one could/should analyze QUIC more generally to see if there are unnecessary covert channels. I assume that since it uses TLS 1.3 then Server.Random is still one, for example.

          1 reply 0 retweets 0 likes
        8. Brian Smith‏ @BRIAN_____ Nov 16
          Replying to @BRIAN_____ @__subodh and

          The harder problem with QUIC is that the server could just send out a junk QUIC record that the client throws away, which contains the)(encrypted) information for the MitM to process. So, probably there's not much one could do.

          1 reply 0 retweets 0 likes
        9. Subodh Iyengar‏ @__subodh Nov 16
          Replying to @BRIAN_____ @matthew_d_green and

          Ya quic is designed ignore things that don’t decrypt so you could technically send a malformed udp packet with anything in it

          0 replies 0 retweets 0 likes
        10. End of conversation

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