Is your feature request related to a problem? Please describe.

Defeat Cold Boot Attacks by wiping LUKS disk encryption during shutdown.

What is a Cold Boot Attacks? See:

• https://www.youtube.com/watch?v=JDaicPIgn9U
• https://en.wikipedia.org/wiki/Cold_boot_attack
• https://blog.f-secure.com/cold-boot-attacks/
• https://www.usenix.org/legacy/event/sec08/tech/full_papers/halderman/halderman.pdf

Describe the solution you'd like
Run cryptsetup close at end of shutdown procedure.

Quote cryptsetup close (previously cryptsetup lukseClose) man page (bold added):

close
Removes the existing mapping and wipes the key from kernel memory.

Maybe cryptsetup close could be done during dracut-shutdown?

This would not wipe all secrets from RAM to defeat a cold boot attack but at least remove one of the most important secrets, the root disk LUKS encryption key.

Describe alternatives you've considered

Linux kernel feature:

This issue can probably not be redirected at the Linux kernel. While a generic solution Wipe RAM to defeat Cold Boot Attacks (systemd/systemd#17242) probably belongs into the kernel, this does not. For the kernel to be able to wipe the memory, encrypted LUKS devices need to be properly closed first. cryptsetup close does that.

systemd feature:

systemd does not wipe the LUKS disk encryption key for root disk from RAM during shutdown. And as I understand systemd developer @poettering Lennart Poettering, this isn't up to systemd either. It's up to the initrd / initramfs. (systemd/systemd#17887)

Quote myself (systemd/systemd#17887 (comment)):

Avoiding all sidelines, keeping this simple, for my understanding and for the record and please correct me if I am wrong... Summary:

"cryptsetup close" of root device during shutdown is already implemented.

Quote systemd developer @poettering Lennart Poettering (systemd/systemd#17887 (comment)):

"cryptsetup close" of root device during shutdown is already implemented.

iff your initrd/distro of choice do so. For the root disk it doesn't matter what systemd does, it matters what the initrd/distro do. hence ping the maintainers of those.