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tehjh's profile
Jann Horn
Jann Horn
Jann Horn
@tehjh

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Jann Horn

@tehjh

works at Google Project Zero. personal account.

Joined August 2011

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    1. hanno‏ @hanno Apr 9
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      Some thoughts about a CSRF tokens and CRIME/BREACH/... alike attacks:

      2 replies 1 retweet 6 likes
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    2. hanno‏ @hanno Apr 9
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      this only works because the CSRF token is always the same on multiple page loads. so what about having a secret key on the server per session, and the token is random+hash(random+csrfkey). verify is hash(firsthalf+csrfkey)==secondhalf.

      2 replies 0 retweets 3 likes
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    3. hanno‏ @hanno Apr 9
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      a) is this a good idea? b) has anyone else already invented this?

      3 replies 0 retweets 0 likes
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    4. hanno‏ @hanno Apr 9
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      we can also fix it with samesite cookies. are samesite cookies the overall solution to all CSRF now? do we even need csrf tokens any more?

      5 replies 0 retweets 0 likes
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    5. Jann Horn‏ @tehjh Apr 10
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      Replying to @hanno

      do you even need samesite for that? I'd kinda expect the Origin header to provide enough protection already, but haven't thought about this a lot

      3 replies 0 retweets 0 likes
    6. Mohit Kumar‏ @unix_root Apr 10
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      Replying to @tehjh @hanno

      I kinda invented something better a few years ago while building a CMS (work is still in progress) for @TheHackersNews. I have put together the logic in the attached screenshot. Let me know if I haven't considered something.pic.twitter.com/g8GAe6dthW

      1 reply 0 retweets 0 likes
      Jann Horn‏ @tehjh Apr 10
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      Replying to @unix_root @hanno @TheHackersNews

      one problem with CSRF tokens is that the renderer knows them; cookies have the nice property that you can keep them isolated in the browser process, and so an attacker who can leak arbitrary data from your renderer process still can't forge requests. this doesn't address that.

      1:15 AM - 10 Apr 2020
      • 1 Retweet
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      • Cyber.SC
      2 replies 1 retweet 1 like
        1. New conversation
        2. Jann Horn‏ @tehjh Apr 10
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          Replying to @tehjh @unix_root and

          but also, it looks like you're using an encryption scheme for something it wasn't designed for, that's not exactly a clean design

          1 reply 0 retweets 0 likes
        3. Mohit Kumar‏ @unix_root Apr 10
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          Replying to @tehjh @hanno @TheHackersNews

          You're right, have to think about it again 😬 I did it a few years back, so have to refresh everything.

          0 replies 0 retweets 1 like
        4. End of conversation
        1. Mohit Kumar‏ @unix_root Apr 10
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          Replying to @tehjh @hanno @TheHackersNews

          Btw, another problem I now see in my code is that any right combination of the cookie value and token on a page would remain valid forever because decryption at server would always work and contain the secret word. Damn! So an attacker can pick on combination and re-use it.

          0 replies 0 retweets 0 likes
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