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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. Matthew Garrett‏ @mjg59 May 22
      • Report Tweet
      • Report NetzDG Violation

      Idea: secure boot signing system that lives on your phone. Bootloader updates trigger a Bluetooth communication that requires affirmative consent on your phone and then signs the bootloader with a key that never leaves your phone.

      14 replies 1 retweet 71 likes
    2. Jann Horn‏ @tehjh May 22
      • Report Tweet
      • Report NetzDG Violation
      Replying to @mjg59

      How is this better than signature verification with distro keys + rollback protection? If you're compiling the bootloader on your machine, you're inherently trusting the machine anyway. If not, whoever built it can sign for you.

      2 replies 0 retweets 1 like
    3. Jann Horn‏ @tehjh May 22
      • Report Tweet
      • Report NetzDG Violation
      Replying to @tehjh @mjg59

      The only point where the user could give meaningful input would be when changing distros or changing bootloaders, right? Or are you talking about bootloader configuration files that are user-editable, like kernel commandline flags?

      1 reply 0 retweets 0 likes
    4. Matthew Garrett‏ @mjg59 May 22
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      Replying to @tehjh

      Bootloader updates - consent here is largely "Is this a request that you expected to occur right now"

      1 reply 0 retweets 0 likes
    5. Jann Horn‏ @tehjh May 22
      • Report Tweet
      • Report NetzDG Violation
      Replying to @mjg59

      Wouldn't I always expect that to occur every time I run a system update?

      1 reply 0 retweets 1 like
    6. Matthew Garrett‏ @mjg59 May 22
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      Replying to @tehjh

      Right

      1 reply 0 retweets 0 likes
    7. Jann Horn‏ @tehjh May 22
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      Replying to @mjg59

      seems like the Security Key model of "tap button on login, confirming that you want the machine to log in to *something* (without communicating what that thing is)", except instead of doing it whenever you log in, you do it whenever the machine tells you to

      1 reply 0 retweets 1 like
    8. Matthew Garrett‏ @mjg59 May 22
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      • Report NetzDG Violation
      Replying to @tehjh

      If a request is being triggered then either: 1) I'm getting a legitimate update 2) My distro's entire infrastructure has been comprehensively owned 3) My machine is already compromised

      1 reply 0 retweets 0 likes
      Jann Horn‏ @tehjh May 22
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      • Report NetzDG Violation
      Replying to @mjg59

      I don't get your point. In all three cases, the user will think "ah, I'm getting a legitimate system update" and press yes. What hurdle does requiring user consent on a separate device create to an attacker?

      10:07 AM - 22 May 2020
      • 1 Like
      • Shakeel Mahate
      2 replies 0 retweets 1 like
        1. New conversation
        2. Matthew Garrett‏ @mjg59 May 22
          • Report Tweet
          • Report NetzDG Violation
          Replying to @tehjh

          In the cases of (2) and (3) I'm already screwed, so it's basically irrelevant. But I'm now protected against someone only having compromised my distribution's signing infrastructure.

          1 reply 0 retweets 0 likes
        3. Jann Horn‏ @tehjh May 22
          • Report Tweet
          • Report NetzDG Violation
          Replying to @mjg59

          Are you talking about an attacker who has the distro's signing key and control over an update server / MITM on the connection to the update server? If so, won't that play out just like case 2? User tries to install updates, sees (evil) bootloader update, installs it?

          1 reply 0 retweets 0 likes
        4. 3 more replies
        1. Jann Horn‏ @tehjh May 22
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          Replying to @tehjh @mjg59

          case 1, the system is currently installing updates. case 2, the system is currently installing updates (from a malicious source). case 3, the attacker either waits until the system is installing updates or pretends that the system is installing updates.

          0 replies 0 retweets 0 likes
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