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Authenticated Boot and Disk Encryption on Linux

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Re: Authenticated Boot and Disk Encryption on Linux

#111

Post by teddyh »

If your attacker is both sophisticated and able to access your hardware directly, the game is over; nothing we can do can currently avoid this.

What we can do is address the scenarios in which an attacker is either unsophisticated or remote. Normal network security takes care of the latter case, and for unsophisticated attackers, a good FDE (Full Disk Encryption) system covers it nicely. For laptops you can either live with typing in a password at every boot, or get a USB key of some kind. For servers with FDE you might want to use something to enable remote and unattended reboots, like (shameless plug) Mandos¹.

1. https://www.recompile.se/mandos

Re: Authenticated Boot and Disk Encryption on Linux

#112

Post by WaitWaitWha »

uuidgen wrote: post #55
phh wrote: post #32

Every time I read stuff about secure boot, "evil maid" attack scenarios come up. And every time, they fail to mention the easiest one. The attack described here involves dismantling the victim's hard drive. I have an attack that isn't defeated by secure boot, and doesn't even require dismantling anything. Steal the original laptop. Take another physically identical unit. Replace it. Copy the login screen of original…

> Copy the login screen of original laptop on a brand new laptop, and have it log the password when the victim types it to you over wifi. This is why you need mutual authentication. The easiest is with 2 passwords. You enter a password, this authenticates you to the system. Now system presents you some secret. It may be a passphrase, something not obvious like a password prompt with a typo, or a splash screen with so…

We used glitter glue on ports for certain traveling individuals. Took pictures of the hardened glue. Very hard for a maid to replicate, be it evil or really good.

Re: Authenticated Boot and Disk Encryption on Linux

#113

Post by g_p »

Foxboron wrote: post #53
g_p wrote: post #36

Earlier quoted context omitted.

An idea I just had around this, for if you run your own PK/KEK/DB chain - is it feasible to "dump" these Option ROMs? If so, you should be able to whitelist their sha256 hashes in your DB database, since the DB can contain an allow-list of hashes, as well as an allow-list of public keys. I'm not familiar with how to view relevant Option ROMs, but if you can "dump" them in the format they will be verified in, you shou…

sysfs doesn't like some optionroms, so using the rom files from there wont work in some cases. Apparently they can be stored in an ACPI table.. but I haven't looked at it. Another alternative is to read the TPM2 eventlog. It should record OptionROM checksums found during boot. $ tpm2_eventlog ./t14_eventlog | grep "BOOT_SERVICES_DRIVER" | wc -l 7 This is essentially what me and Trammell Hudson has been thinking about…

Good idea RE the TPM event log - that should show the definitive perceived hash of the option ROM.

Will need to see if I have any computers that require an Option ROM - somehow I suspect shipped-with-Linux Dell XPS laptops aren't going to be good test candidates.

Re: Authenticated Boot and Disk Encryption on Linux

#115

Post by jonathanstrange »

teddyh wrote: post #111

If your attacker is both sophisticated and able to access your hardware directly, the game is over; nothing we can do can currently avoid this. What we can do is address the scenarios in which an attacker is either unsophisticated or remote . Normal network security takes care of the latter case, and for unsophisticated attackers, a good FDE (Full Disk Encryption) system covers it nicely. For laptops you can either l…

Well, you can probably annoy at least some attackers by using tamper-proof seals on your PC case and act accordingly if they are broken, because that would likely prevent them from conducting the first physical attack. But that won't help in the long run.

Outstanding locks on a reinforced door and a combination of visible and hidden cameras in the hallway are probably more effective.

Re: Authenticated Boot and Disk Encryption on Linux

#116

Post by zokier »

vbezhenar wrote: post #63

So basically an issue is that initramfs is not validated. Is it even possible to resolve that issue? If new grub version adds forced initramfs validation when run under secure boot mode, attacker can just install old grub which is still signed, but allows for unsigned initramfs. Of course everything but /boot must just be encrypted, there's no reason not to.

You don't need separate initramfs file these days, you can bake it into the kernel executable which you can then sign

Re: Authenticated Boot and Disk Encryption on Linux

#117

Post by WaitWaitWha »

phh wrote: post #47
nsajko wrote: post #35

Earlier quoted context omitted.

Replicating the chassis (including the scratches, etc.) and other laptop parts is the hardest part of your attack. I assume you don't know about the nail-polish with glitter based protection? Even "copying the login screen" is not necessarily easy.

You know the scratches on the chassis of your laptop? I definitely don't. If someone replaces my laptop with a brand new one, I'll notice something is off, but I wouldn't be surprised I'd notice /after/ typing my password. If rather than brand new, it's replaced another laptop with approximately same age/usage, I would most definitely not notice. > I assume you don't know about the nail-polish with glitter based prot…

>> I assume you don't know about the nail-polish with glitter based protection?

>Nope, can you explain?

You take clear, semi-liquid glue that hardens. The glue has various colored Mylar flexes (aka glitter) floating in it. Slather it onto a device (we did it for exposed ports on devices). The glue is semi-liquid so it will flow reasonably. Once the glue hardens, the orientation, distribution, coloring and such of the flex are set. Take picture(s) of the hardened glue. (just search for glitter glue)

Reproducing the complexity of the glue plus glitter is very hard. Possible attacks is attempting to remove it, and inserting it back in. The right glitter glue is quite brittle so hard to remove it. Heating it will make it hazy before pliable, and cooling it makes them even more brittle. Breaks show up as while surface inclusion in the glue.

Re: Authenticated Boot and Disk Encryption on Linux

#118

Post by vbernat »

vbezhenar wrote: post #63

So basically an issue is that initramfs is not validated. Is it even possible to resolve that issue? If new grub version adds forced initramfs validation when run under secure boot mode, attacker can just install old grub which is still signed, but allows for unsigned initramfs. Of course everything but /boot must just be encrypted, there's no reason not to.

When upgrading, you have to remove old PCR states, so rolling back to an older version is detected.

Re: Authenticated Boot and Disk Encryption on Linux

#119

Post by gear54rus »

teddyh wrote: post #111

If your attacker is both sophisticated and able to access your hardware directly, the game is over; nothing we can do can currently avoid this. What we can do is address the scenarios in which an attacker is either unsophisticated or remote . Normal network security takes care of the latter case, and for unsophisticated attackers, a good FDE (Full Disk Encryption) system covers it nicely. For laptops you can either l…

How does one go about breaking FDE tho? If it's secured by a password that's only in your mind.

Re: Authenticated Boot and Disk Encryption on Linux

#120

Post by [deleted] »

teddyh wrote: post #111

If your attacker is both sophisticated and able to access your hardware directly, the game is over; nothing we can do can currently avoid this. What we can do is address the scenarios in which an attacker is either unsophisticated or remote . Normal network security takes care of the latter case, and for unsophisticated attackers, a good FDE (Full Disk Encryption) system covers it nicely. For laptops you can either l…

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