4 ms·

One interesting use for this could be signing it with your own secure boot keys. This could let you lock a machine to only boot your system image and not others

by shawnz 7y ago

One interesting use for this could be signing it with your own secure boot keys. This could let you lock a machine to only boot your system image and not others.

p_l 7y ago
Standard Windows bootloader already does that, it's part of supported deployment flow in highest security setting - in fact part of why MS requires that computers with certain Windows-related branding (the part about stickers "designed for windows" etc., I just don't remember which one) have to enable end users to replace platform keys.
- rekoil 7y ago
  Except the same keys have been used to sign some EFI loaders from other vendors, namely Kaspersky Rescue Disk 18, so it isn't really as locked down as they would have us believe. https://habr.com/en/post/446238/ https://habr.com/en/post/446238/
  - beojan 7y ago
    Not if you replace the keys with your own.
    - rekoil 7y ago
      Sure, and I do that, but most users will not, they will select Secure Boot and think that their boot is now secure.
  - p_l 7y ago
    There are two keys distributed by MS - one for Windows, one for third party applications. The latter one is used by Linux shim bootloader and the like. MS also requires that all devices that are supposed to be "full featured" support replacing all keys and loading user keys, and the highest security deployment setup for Windows Enterprise requires that you sign windows bootloader (or, more likely, sign the hash of the specific binary you are using) yourself.
    - shawnz 7y ago
      > the highest security deployment setup for Windows Enterprise requires that you sign windows bootloader (or, more likely, sign the hash of the specific binary you are using) yourself. To my knowledge that's not possible with the Microsoft bootloader, you need to use Microsoft's keys, hence why I am suggesting that this open source bootloader could be useful. Can you provide some more information about such a setup?
      - p_l 7y ago
        The basic procedure is as follows: - Remove all keys (switch to Setup mode) - Setup your own PKI and platform keys - Sign hash of specific EFI files and load those signatures into EFI The last part doesn't require modifying files themselves, as you're locking specific files. The firmware will make a hash of the file, and verify that it's on permitted list (the list is signed)
        shawnz 7y ago
        If I'm not mistaken it's actually a hash of the file's signature that you have to register, not a hash of the file itself. And Bootmgr will not allow you to change its signature. Thus any computer that is configured to boot Windows with secure boot will be able to boot any copy of Windows.
      - jedieaston 7y ago
        This document is aimed at OEMs, but they specifically say that high-security environments can generate Secure Boot keys and use them on their devices in conjunction with their own Windows image. (I’d imagine that you need the Windows SDK and some know how/MS consulting to get it working, though) https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-secure-boot-key-creation-and-management-guidance#2-key-management-solutions https://docs.microsoft.com/en-us/windows-hardware/manufactur...
        shawnz 7y ago
        This document is about generating the platform key, but changing the platform key alone doesn't allow you to do what I'm suggesting. Even after setting your own platform key you would still need to trust the key for Microsoft's bootloader. See section 1.4.1: > The Microsoft Windows Production PCA 2011 with a SHA-1 Cert Hash of 58 0a 6f 4c c4 e4 b6 69 b9 eb dc 1b 2b 3e 08 7b 80 d0 67 8d must be included in db in order to allow the Windows OS Loader to load.

by shawnz 7y ago

One interesting use for this could be signing it with your own secure boot keys. This could let you lock a machine to only boot your system image and not others.

p_l 7y ago

Standard Windows bootloader already does that, it's part of supported deployment flow in highest security setting - in fact part of why MS requires that computers with certain Windows-related branding (the part about stickers "designed for windows" etc., I just don't remember which one) have to enable end users to replace platform keys.

rekoil 7y ago
Except the same keys have been used to sign some EFI loaders from other vendors, namely Kaspersky Rescue Disk 18, so it isn't really as locked down as they would have us believe. https://habr.com/en/post/446238/ https://habr.com/en/post/446238/
- beojan 7y ago
  Not if you replace the keys with your own.
  - rekoil 7y ago
    Sure, and I do that, but most users will not, they will select Secure Boot and think that their boot is now secure.
- p_l 7y ago
  There are two keys distributed by MS - one for Windows, one for third party applications. The latter one is used by Linux shim bootloader and the like. MS also requires that all devices that are supposed to be "full featured" support replacing all keys and loading user keys, and the highest security deployment setup for Windows Enterprise requires that you sign windows bootloader (or, more likely, sign the hash of the specific binary you are using) yourself.
  - shawnz 7y ago
    > the highest security deployment setup for Windows Enterprise requires that you sign windows bootloader (or, more likely, sign the hash of the specific binary you are using) yourself. To my knowledge that's not possible with the Microsoft bootloader, you need to use Microsoft's keys, hence why I am suggesting that this open source bootloader could be useful. Can you provide some more information about such a setup?
    - p_l 7y ago
      The basic procedure is as follows: - Remove all keys (switch to Setup mode) - Setup your own PKI and platform keys - Sign hash of specific EFI files and load those signatures into EFI The last part doesn't require modifying files themselves, as you're locking specific files. The firmware will make a hash of the file, and verify that it's on permitted list (the list is signed)
      - shawnz 7y ago
        If I'm not mistaken it's actually a hash of the file's signature that you have to register, not a hash of the file itself. And Bootmgr will not allow you to change its signature. Thus any computer that is configured to boot Windows with secure boot will be able to boot any copy of Windows.
    - jedieaston 7y ago
      This document is aimed at OEMs, but they specifically say that high-security environments can generate Secure Boot keys and use them on their devices in conjunction with their own Windows image. (I’d imagine that you need the Windows SDK and some know how/MS consulting to get it working, though) https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-secure-boot-key-creation-and-management-guidance#2-key-management-solutions https://docs.microsoft.com/en-us/windows-hardware/manufactur...
      - shawnz 7y ago
        This document is about generating the platform key, but changing the platform key alone doesn't allow you to do what I'm suggesting. Even after setting your own platform key you would still need to trust the key for Microsoft's bootloader. See section 1.4.1: > The Microsoft Windows Production PCA 2011 with a SHA-1 Cert Hash of 58 0a 6f 4c c4 e4 b6 69 b9 eb dc 1b 2b 3e 08 7b 80 d0 67 8d must be included in db in order to allow the Windows OS Loader to load.