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From: Milan Broz <>
To: John Smith <>,
Subject: Re: Are the keys of mounted encrypted disks secured during reboot?
Date: Wed, 28 Dec 2022 09:51:55 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 12/26/22 21:10, John Smith wrote:
> I'm asking about when a regular shutdown/reboot/suspend-to-disk is
> issued. In most cases the rootfs volume is not unmounted because that
> would require a pivot_root to a special initrd/ramdisk-rootfs just for
> powering off.
> So that would mean the device isn't deactivated via cryptsetup -
> because that would fail.

Cryptsetup (libcryptsetup) is just library that performs the job,
it does not run itself any actions.
Once it is called, keys should be wiped.

The deactivation/reboot/suspend is handled by init scripts, usually systemd
units these days - so check there. It really depends on system configuration.

However, last time we played with memory scan for keys after reboot,
cold boot is no longer such a problem as memory is wiped during reboot
on modern hw (but virtual machines images is a different problem).


> In that case, when the kernel is preparing to reboot/poweroff, will it
> wipe the keys or just leave them there vulnerable to cold boot or
> forensics?
> On Mon, Dec 26, 2022 at 7:42 PM Milan Broz <> wrote:
>> On 12/26/22 20:13, John Smith wrote:
>>> During the course of proper shutdown/reboot/suspend-to-disk, does the
>>> kernel securely erase (or at least free memory of - as it pertains to
>>> init_on_free=1) encryption keys of all dmcrypt/luks systems which
>>> remained mounted?
>> If the device is properly deactivated, then keys are always wiped.
>> (Actually, with LUKS2, dm-crypt no longer keeps own copy of the key, it
>> is stored in kernel keyring only for activation and then, obviously, in kernel
>> crypto where is is directly used for encryption. So if it is not
>> deactivated, it is responsibility of these subsystems to wipe it on reboot.)
>> For suspend to ram, it is more complicated - there is a way how to wipe key
>> and freeze device temporarily (see luksSuspend), but I do no think many systems
>> actually use it. Debian has cryptsetup-suspend that can do this AFAIK.
>> For suspend to disk, the memory should be written to encrypted device.
>> (And RAM contents disappears after some short time with no power anyway.)
>> Milan

      reply	other threads:[~2022-12-28  8:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-26 19:13 Are the keys of mounted encrypted disks secured during reboot? John Smith
2022-12-26 19:42 ` Milan Broz
2022-12-26 20:10   ` John Smith
2022-12-28  8:51     ` Milan Broz [this message]

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