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taviso's profile
Tavis Ormandy
Tavis Ormandy
Tavis Ormandy
Verified account
@taviso

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Tavis OrmandyVerified account

@taviso

Vulnerability researcher at Google. This is a personal stream, opinions expressed are mine.

California
taviso.decsystem.org
Joined April 2008

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    1. Tavis Ormandy‏Verified account @taviso 18 Nov 2019
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      Replying to @saleemrash1d @alexstamos

      Right, never seen before, but you can prove that you've seen it. I think that's good enough. The software has to be distributed in some protected form, so you can also sign the hashes and verify a classifier said they're nudes before automatic blocking if you like.

      1 reply 0 retweets 0 likes
    2. Saleem Rashid‏ @saleemrash1d 18 Nov 2019
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      Replying to @taviso @alexstamos

      this is a compelling idea (hash it locally after running a classifier in a trusted execution environment) and i think i missed this point in your original argument. is this practical yet? what needs to happen to make it so?

      1 reply 0 retweets 1 like
    3. Tavis Ormandy‏Verified account @taviso 18 Nov 2019
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      Replying to @saleemrash1d @alexstamos

      I believe it's practical and that I could build it, Alex says it isn't but handwaves away anyone asking why not. So, who knows...

      1 reply 0 retweets 0 likes
    4. Saleem Rashid‏ @saleemrash1d 18 Nov 2019
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      Replying to @taviso @alexstamos

      i think there are rough edges: - if your classifier mistakenly decides that a photo shouldn't be automatically blocked, what happens? - i guess you have to rate limit the classifier (depends on the limitations of your TEE); solved by making PoW an input to the classifier?

      0 replies 0 retweets 0 likes
    5. Tavis Ormandy‏Verified account @taviso 18 Nov 2019
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      Replying to @taviso @saleemrash1d @alexstamos

      I don't know if I'm convinced it's necessary, I think just standard procedures (require account, rate limiting, bans, etc) will prevent abuse and just proving you've seen it first and delaying until moderation is good enough. But if people disagree, the problems are solvable.

      1 reply 0 retweets 0 likes
    6. Saleem Rashid‏ @saleemrash1d 18 Nov 2019
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      Replying to @taviso @alexstamos

      i don't know enough about the false positive/negative rates of these image hashing algorithms to draw a conclusion here. "seen it first" on its own is such a fickle metric because there's an entire Internet of content that Facebook hasn't "seen" yet.

      1 reply 0 retweets 0 likes
    7. Saleem Rashid‏ @saleemrash1d 18 Nov 2019
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      Replying to @saleemrash1d @taviso @alexstamos

      but it seems to me that, regardless of the pitfalls of this method, you could deploy both at once and collect at least some data on its effectiveness in practice (not comprehensive though, because people won't necessarily upload adversarial input while the old system is in place)

      1 reply 0 retweets 0 likes
    8. Tavis Ormandy‏Verified account @taviso 18 Nov 2019
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      Replying to @saleemrash1d @alexstamos

      It's not blocking though, it's just temporarily delaying sharing while you're moderating it, with a pretty good signal that you own the image, and options for improving the signal. Is that really so bad that we should give up and say, "just mail facebook employees your nudes"?

      1 reply 0 retweets 0 likes
    9. Saleem Rashid‏ @saleemrash1d 18 Nov 2019
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      Replying to @taviso @alexstamos

      Saleem Rashid Retweeted Saleem Rashid

      so we're on the same page here, you started with the premise of "my solution is always >= Facebook's solution" and that therefore Alex's point made no sense. i was merely presenting the case where it did have merit.https://twitter.com/saleemrash1d/status/1196513128357515267 …

      Saleem Rashid added,

      Saleem Rashid @saleemrash1d
      Replying to @taviso @alexstamos
      i'm not making a judgement here, but Alex's point makes sense to me if you whitelist the photos upfront, there's an initial delay but you can thereafter immediately block the photo upon detection
      2 replies 0 retweets 0 likes
      Tavis Ormandy‏Verified account @taviso 18 Nov 2019
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      Replying to @saleemrash1d @alexstamos

      Tavis Ormandy Retweeted Tavis Ormandy

      No, I've already explained that both systems have that limitation.https://twitter.com/taviso/status/1196524371898028032 …

      Tavis Ormandy added,

      Tavis OrmandyVerified account @taviso
      Replying to @saleemrash1d @alexstamos
      No it doesn't. If the photo is already being shared when you submit it, it doesn't stop until moderation. That is the same in both systems. If it hasn't been shared yet, it can be blocked first in both systems. The difference is no new people see your nudes until abuse with hash.
      1:06 PM - 18 Nov 2019
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Saleem Rashid‏ @saleemrash1d 18 Nov 2019
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          Replying to @taviso @alexstamos

          i haven't at all mentioned the case where the photo has already been shared.

          1 reply 0 retweets 1 like
        3. Tavis Ormandy‏Verified account @taviso 18 Nov 2019
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          Replying to @saleemrash1d @alexstamos

          There are only two possible cases. It has already been shared, or it hasn't. In the first, both systems require a moderation delay. In the second, both systems can prevent sharing. Therefore, >= is correct, because the second system doesn't require mailing your nudes to facebook.

          0 replies 0 retweets 1 like
        4. End of conversation

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