Arch Linux

ArchGuest24

Member

Registered: 2023-09-16

Posts: 1

slow to unlock LUKS disk on start up

I have a fresh install of arch with /boot (encrypted because it's on the same partition as root), and /efi (unencrypted).
It takes ~5s when "Attempting to decrypt master key".

Is it possible to reduce the decrypt time to ~2s? Should I have /boot unencrypted?

I have random.trust_cpu=on in my GRUB_CMDLINE_LINUX.

Device             Start       End   Sectors   Size Type
/dev/nvme0n1p1      2048    534527    532480   260M EFI System
/dev/nvme0n1p2    534528    567295     32768    16M Microsoft reserved
/dev/nvme0n1p3    567296 128112639 127545344  60.8G Microsoft basic data
/dev/nvme0n1p4 496021504 500117503   4096000     2G Windows recovery environment
/dev/nvme0n1p5 128112640 496021503 367908864 175.4G Linux filesystem

$ systemd-analyze
Startup finished in 8.841s (firmware) + 54.149s (loader) + 5.057s (kernel) + 2.664s (userspace) = 1min 10.712s 
graphical.target reached after 2.664s in userspace.
$ systemd-analyze blame
795ms NetworkManager.service
621ms dev-mapper-vg\x2droot.device
272ms systemd-udev-trigger.service
253ms systemd-remount-fs.service
235ms systemd-modules-load.service
233ms systemd-tmpfiles-setup.service
201ms efi.mount
158ms modprobe@fuse.service
142ms user@1000.service
128ms lvm2-monitor.service
126ms modprobe@drm.service
112ms systemd-tmpfiles-setup-dev-early.service
...

$ cryptsetup luksDump /dev/nvme0n1p5 
LUKS header information for /dev/nvme0n1p5

Version:        1
Cipher name:    aes
Cipher mode:    xts-plain64
Hash spec:      sha512
Payload offset: 4096
MK bits:        512
MK digest:      64 08 f8 ea b9 6a 52 15 4d 33 22 d0 6a 80 70 23 a3 eb c8 62 
MK salt:        5e ca 05 df 17 64 61 99 55 18 fe ba 0b b6 ae 47 
                10 dd c1 d0 b3 7b 6f 6c 9d d2 3d 38 21 21 11 43 
MK iterations:  303758
UUID:           a8bdc8af-87b6-4abc-849b-83c4031d7456

Key Slot 0: DISABLED
Key Slot 1: ENABLED
        Iterations:             6668208
        Salt:                   d5 07 03 8d cb cd ee 76 15 72 7a 6a f5 a3 49 ab 
                                69 d6 20 54 bd 8b b5 aa b3 ed d4 49 10 72 5b 8b 
        Key material offset:    512
        AF stripes:             4000
Key Slot 2: ENABLED
        Iterations:             1966080
        Salt:                   a6 98 e3 54 f2 58 95 e5 fb f8 2a 99 37 9d 92 9c 
                                65 f5 fe 9e d7 cd bb c4 65 87 3e 05 52 73 d6 97 
        Key material offset:    1016
        AF stripes:             4000

$ cryptsetup benchmark
# Tests are approximate using memory only (no storage IO).
PBKDF2-sha1      3163125 iterations per second for 256-bit key
PBKDF2-sha256    6452775 iterations per second for 256-bit key
PBKDF2-sha512    2421653 iterations per second for 256-bit key
PBKDF2-ripemd160 1267927 iterations per second for 256-bit key
PBKDF2-whirlpool 1012138 iterations per second for 256-bit key
argon2i       8 iterations, 1048576 memory, 4 parallel threads (CPUs) for 256-bit key (requested 2000 ms time)
argon2id      8 iterations, 1048576 memory, 4 parallel threads (CPUs) for 256-bit key (requested 2000 ms time)
#     Algorithm |       Key |      Encryption |      Decryption
        aes-cbc        128b      1763.5 MiB/s      6501.5 MiB/s
    serpent-cbc        128b       122.1 MiB/s       846.5 MiB/s
    twofish-cbc        128b       262.8 MiB/s       546.0 MiB/s
        aes-cbc        256b      1390.3 MiB/s      5400.7 MiB/s
    serpent-cbc        256b       124.7 MiB/s       842.3 MiB/s
    twofish-cbc        256b       267.3 MiB/s       552.3 MiB/s
        aes-xts        256b      5111.5 MiB/s      5101.4 MiB/s
    serpent-xts        256b       738.2 MiB/s       757.2 MiB/s
    twofish-xts        256b       511.5 MiB/s       517.9 MiB/s
        aes-xts        512b      4630.5 MiB/s      4615.5 MiB/s
    serpent-xts        512b       751.3 MiB/s       766.0 MiB/s
    twofish-xts        512b       516.4 MiB/s       520.8 MiB/s

Last edited by ArchGuest24 (2023-09-16 12:48:55)

2ManyDogs

Forum Fellow

Registered: 2012-01-15

Posts: 4,648

Re: slow to unlock LUKS disk on start up

Please edit your post and use [ code ] tags (not quote tags) when posting output. This makes the output easier to read and provides a scroll box for long output.

https://wiki.archlinux.org/title/Genera … s_and_code
https://bbs.archlinux.org/help.php#bbcode

frostschutz

Member

Registered: 2013-11-15

Posts: 1,647

Re: slow to unlock LUKS disk on start up

Grub is known to be slow when decrypting. That's just how it is, if you don't like it, go with unencrypted bootloader + kernel + initrd. You can still encrypt everything else.

Also, you have two keyslots. Make sure you put the passphrase for Grub into the first one; otherwise Grub will have to try both, which takes twice as long. Same for encrypt hook in initramfs; if it has to try both keyslots, it will take longer than strictly necessary.

Another way to make Grub cryptodisk faster is to drastically reduce the iteration counts. However this means you lose the bruteforce protection that LUKS normally offers. It's not safe without a very high entropy passphrase.