Comment by deng
2 hours ago
> Except that, for more than two years, the encryption key remained resident in memory across suspend, leaving it there for the taking by anyone who seized the still-powered laptop.
I don't get it. Obviously, the laptop is locked when it resumes, how is that key "for the taking by anyone"? I'm not saying it is impossible to read out RAM from a locked laptop, but surely not by "anyone".
Anyone with physical access. I think it is understandable from the phrase.
There is a common misconception about how lock-screens in general work - they usually just prevents using the current hardware and software as it is to access the current OS. But the disk encryption is the main thing that prevents modification and other kind of access to actual data. And if the disk encryption key is lying in the memory, then effectively, the disk encryption is bypassed if someone can access the machine physically and assuming that there are no sufficient tampering protections in place for that machine.
Anyone with physical access, significant tools, and experience. The FBI has people who can pull data out of memory after freezing the RAM but the average laptop thief doesn’t so how serious this is depends significantly on your threat model. If you’re not a major criminal, bitcoin whale, or intelligence target this is almost certainly academic.
> If you’re not a major criminal, bitcoin whale, or intelligence target this is almost certainly academic.
Thanks, that's what I thought.
> Anyone with physical access. I think it is understandable from the phrase.
Sorry, I'm probably dense, I still don't get it. You steal a laptop, you open it, the screen is locked with a password/fingerprint whatever. How do you read out the RAM from that laptop?
Several options. One is you restart and boot from a live system where you are root, and then dump all memory. This is described in the paper with the witty title "Lest We Remember: Cold Boot Attacks on Encryption Keys":
https://www.usenix.org/legacy/event/sec08/tech/full_papers/h...
Other options: DMA attacks. Also you never know what the Intel Management Engine hidden in your computer is doing. It's running a version of Minix you don't have any control over, and it has full access to memory.
>How do you read out the RAM from that laptop?
the term to look up is "cold boot attack" (https://en.wikipedia.org/wiki/Cold_boot_attack).
tons of cool live demonstrations of how it works on youtube if you've got the 20-40 minutes to spare
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There are attacks that allow dumping RAM if the device is powered on though and you have physical access. Depending on config it may be very easy (just plug in a dumper over Thunderbolt on USB C and do direct memory access) or hard (freeze and swap physical RAM to an unlocked machine).. but the idea was defense-in-depth here; a well configured device should both be hard to dump RAM on and it should not give encryption keys if an attacker succeeds.
you dump the physical memory, then decrypt the disk offline