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something I hadn't really considered about hard disk encryption, before reading this, is how it could protect against compromised disk controllers. if the OS en
by munin 13y ago
something I hadn't really considered about hard disk encryption, before reading this, is how it could protect against compromised disk controllers. if the OS encrypts the data stored on the disk, it would be a lot harder (perhaps, with the right composition, impossible) for a malicious disk controller to insert/change/modify important data (like code, or password files) stored on the computer.
we think of the system as a holistic entity, but turned on its head, you can see how the inside of a computer is just a network...
- im3w1l 13y agoMaybe I misunderstood, but didn't the harddrive have direct memory access (DMA)?
- __david__ 13y agoIt had DMA to its own memory, not to the host computer's memory.
- MBCook 13y agoThe DMA mentioned in the article was internal to the drive, between the hardware interfaces and it's internal cache. The drive did not have DMA access to system memory.
- 0x0 13y agoEven though it wasn't discussed in the article, I think firewire and thunderbolt external drives DO have direct DMA access to system memory. Google for SBP-2 and DMA, and a bunch of articles about protecting against firewire attacks against full-disk-encryption (among other things) appear.
- MBCook 13y agoI know you're right on FW. I believe DMA was designed in because they recognized that the CPUs of the time weren't powerful enough to move uncompressed full-resolution video from around. I don't know about Thunderbolt, but I'd expect you're right.
- fragmede 13y agoThunderbolt is just pci-express in new clothes, so yes, it does.
- MBCook 13y agoGood point.
- fiskfiskfisk 13y agoIIRC DMA was designed to allow peripherals (floppy drives, parallell ports, etc.) to move data from their input lines to regular memory without having to bother the CPU. Uncompressed, full resolution video wasn't too much of a real concern back in the days of the 80286 :-)
- nicolast 13y agoHence http://www.breaknenter.org/projects/inception/ http://www.breaknenter.org/projects/inception/ and similar attacks.
- deleted 13y ago[deleted]
- munin 13y agoyes there is, you encrypt the OS that is stored on the hard drive edit: sorry, chain looks like this: BIOS reads boot block from hard drive, checks digital signature, signature invalid, boot fails. BIOS check for signature works in concert with TPM to do key storage, so you're fine. albeit, sleeping with 'evil' technology like UEFI and TPM.
- AnthonyMouse 13y agoYou're still going to have the "who can you trust" problem. If you're worried about a compromised disk controller then you ought to be worried about a compromised BIOS or TPM too.
- yew 13y agoOught you? Those are all different bits of hardware. One being subverted doesn't mean the others are - if nothing else, the attacker isn't likely to have a vulnerability for every combination of firmware and chip. This sort of attack is usually going to be more trouble than it's worth to execute, but that doesn't mean it's out of reach for a motivated, educated individual.
- AnthonyMouse 13y agoYou don't need a combination, just compromising the BIOS gets you root. You don't need to separately compromise the disk firmware, it's either or. The point is that it's the same kind of attack. Relying on the BIOS may save you from an attack on the disk firmware but that doesn't much help if the same class of attack is still effective against the BIOS.
- yew 13y agoSure. My point is there's no guarantee the attacker will be able to compromise the TPM or BIOS just because they can compromise the disk controller. I'd bet most systems see different disk controllers more often than they see different BIOS chips. I'd bet (though not at so high odds) that reasonably secure TPM chips are relatively easier to find outside of the high-end server niche. I'd bet that most non-state actors executing this sort of attack wouldn't have equivalent exploits ready for many different types of hardware. All of those factors shift risk around (again, what little risk there is from this sort of vulnerability). Forgetting about patching a hole here because of an equal-sized hole over there is silly.