Comment by bitbasher
3 hours ago
I don't see any other way? When you sleep (suspend to RAM), everything is stored in RAM and is encrypted but the master key is present in kernel memory (if I recall correctly).
However, if you hibernate (suspend to disk) the entire contents of RAM (including the master key) is written/encrypted to disk and the RAM is cleared.
When you wake the machine up you have to re-enter the passphrase to decrypt the master key to re-load disk contents back to memory.
Yes, if you simply suspend your laptop on most stock Linux distributions, then everything including the master key is still kept in memory. But Debian pioneered the (optional) cryptsetup-suspend addon. This issues a luksSuspend command which is supposed to wipe the key from memory, and on resume asks you to resupply your passphrase.
Up to kernel 6.8, this worked as described; starting with kernel 6.9, it silently didn't.
I've been wondering why hibernate didn't work with encryption, because this seems like the extremely obvious way to handle it - glad to hear it does exist!
But yeah, also rather obviously it's inherently a bit leak-prone. Though it seems probably pretty simple to test, just hibernate and scan all stored data. They could probably even do it on shutdown, as a hash of the key data would be sufficient to detect the key.
So you would still be asked for a passphrase, even though it's already available?
Exactly. Cryptsetup wouldn't know about the extra copy of the volume key in kernel memory. Which is why, dramatically, it appeared secure ("surely I wouldn't be asked to resupply the passphrase if the volume key is still in memory, right?").
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FYI: VeraCrypt is not the defacto encryption software for Windows.
Oh, which one is it?
(You don't mean BitLocker, right?)
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Both Intel/AMD CPUs produced in the last 5 years or so support full transparent (to the OS) memory encryption. So cold boot attacks are a thing of the past if you enable this feature (it's typically disabled because it reduces RAM speed by about 0.5%).
The impact on performance is more along the lines of 1-2% on AMD (though it likely varies by generation (I did extensive benchmarking on Renoir wrt throughput/latency/gpu). But yes small enough to be insignificant unless you run LLMs or game on the iGPU. I imagine that it also uses marginally more power.
AMD also has a second encryption mode where the OS decides what gets transparently encrypted, it doesn't have to be everything. But that mode is poorly documented (or at least the documentation isn't accessible to peasants like me)
Recent news is that this isn't shipping on some consumer-grade CPUs from AMD. There, made it explicit enough there's no room for conversation. Here's the link:
https://arstechnica.com/security/2026/06/users-cry-foul-afte...
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