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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. thaidn‏ @XorNinja Jun 8
      Replying to @XorNinja @BRIAN_____ and

      Something to think about: suppose there's a deterministic carry mispropagation bug that can be triggered with 1% of the scalar values. Is it possible to extract the private key?

      1 reply 0 retweets 1 like
    2. thaidn‏ @XorNinja Jun 8
      Replying to @XorNinja @BRIAN_____ and

      Point-on-curve check can detect mispropagation bugs, but I'm not sure whether these bugs leak the Ed25519 private key. Since the bugs are deterministic, the adversary cannot obtain two different R values for the same nonce and message. @jurajsomorovsky thoughts?

      3 replies 0 retweets 0 likes
    3. Brian Smith‏ @BRIAN_____ Jun 8
      Replying to @XorNinja @bmastenbrook and

      I think this is probably something beyond what's reasonable to solve on Twitter. What I'm really wondering is what are the near-zero-cost countermeasures that can reduce the likelihood of a Rowhammer-like attack the most, ideally without randomization the scalar mult.

      2 replies 0 retweets 1 like
    4. Henry de Valence‏ @hdevalence Jun 8
      Replying to @BRIAN_____ @XorNinja and

      The thing I don’t understand in this discussion is why randomizing the nonce (by inserting random data into the hash) is insufficient?

      1 reply 0 retweets 2 likes
    5. Brian Smith‏ @BRIAN_____ Jun 8
      Replying to @hdevalence @XorNinja and

      Ideally the library implementing EdDSA would implement countermeasures that work regardless of the message content, and which are 100% compatible with the standard.

      1 reply 0 retweets 2 likes
    6. Henry de Valence‏ @hdevalence Jun 8
      Replying to @BRIAN_____ @XorNinja and

      Doesn’t Trevor’s suggestion meet those properties? The randomness is independent of the message, and only used to generate the nonce, which is known only to the signer.

      1 reply 0 retweets 0 likes
    7. Brian Smith‏ @BRIAN_____ Jun 8
      Replying to @hdevalence @XorNinja and

      The standard says the signatures are deterministic so you have to generate the same signature given the same inputs.

      1 reply 0 retweets 1 like
    8. Henry de Valence‏ @hdevalence Jun 8
      Replying to @BRIAN_____ @XorNinja and

      I see. Do you know of any higher-level protocols/systems that rely on this property?

      1 reply 0 retweets 0 likes
    9. juraj somorovsky‏ @jurajsomorovsky Jun 9
      Replying to @hdevalence @BRIAN_____ and

      You can take a look at our paper, https://eprint.iacr.org/2017/1014.pdf , Section 7. There we analyze different protocols and their usage of EdDSA. tl;dr: Most of the protocols generate fresh random values which are signed along with the message, so you cannot enforce signature "re-computation"

      1 reply 0 retweets 0 likes
    10. Brian Smith‏ @BRIAN_____ Jun 9
      Replying to @jurajsomorovsky @hdevalence and

      If you can flip buts with Rowhammer then depending on PRNG implementation you might be able to reset PRNG state to replay the same output twice in a row, e.g. many ChaCah20-based PRNGs are used. This would create problems both for randomized EdDSA and for apps w/ nonces in msgs.

      1 reply 0 retweets 0 likes
      Brian Smith‏ @BRIAN_____ Jun 9
      Replying to @BRIAN_____ @jurajsomorovsky and

      Further, if you can flip a bit with Rowhammer then you could flip the "TLS handshake is complete" flag and cause the app to accept unauthenticated/unencrypted input and/or write unencrypted output. https://bugzilla.mozilla.org/show_bug.cgi?id=919877 … shows such a magic bit exists/existed in real life.

      3:37 AM - 9 Jun 2018
      • 3 Retweets
      • 6 Likes
      • Royce Williams Marius Gedminas pepe le vamp Daniel Hirche Plore GrumpSec Spottycat 🏳️‍🌈🐆 Ryan Sleevi
      1 reply 3 retweets 6 likes
        1. New conversation
        2. Brian Smith‏ @BRIAN_____ Jun 9
          Replying to @BRIAN_____ @jurajsomorovsky and

          In general, I am skeptical that we need crypto-specific mitigations for Rowhammer and similar bugs, because it seems likely there are always other magic bits that could be flipped to cause the same or worse damage.

          1 reply 0 retweets 2 likes
        3. juraj somorovsky‏ @jurajsomorovsky Jun 9
          Replying to @BRIAN_____ @hdevalence and

          This is true, you could e.g. flip a specific bit to get admin rights. The small motivation for our rowhammer eddsa attacks was that in certain scenarios you could flip ANY bit in a large message to be signed and obtain the key

          1 reply 0 retweets 3 likes
        4. Matthew Green‏ @matthew_d_green Jun 9
          Replying to @jurajsomorovsky @BRIAN_____ and

          What?

          1 reply 0 retweets 1 like
        5. Antonio Sanso‏Verified account @asanso Jun 9
          Replying to @matthew_d_green @jurajsomorovsky and

          Indeed, what?

          4 replies 0 retweets 0 likes
        6. juraj somorovsky‏ @jurajsomorovsky Jun 9
          Replying to @asanso @matthew_d_green and

          The Problem with rowhammer is that depending on the scenario sometimes it is hard to flip specific bits, so that you could get admin rights or modify access flags (I am not an expert on rowhammer, please do not ask more :))

          0 replies 0 retweets 1 like
        7. End of conversation

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