Re: Slow unlock of the LUKS device at boot

On 29. 11. 22 20:50, Lamy Geier wrote:
> My boot partition (/dev/nvme0n1p1) is using LUKS1. And another partition
> (/dev/nvme0n1p5) is using LUKS2 which has LVM with root volume,  home
> volume and swap volumes. Both of these have same passphrase.
> 
> I am using Grub. While booting I enter the passphrase to unlock the boot
> partition. To automatically unlock the partition with LVM volumes, I
> have created a keyfile (boot_os.keyfile) which is stored in the device
> itself, which is used to unlock it. I have created it as follows:
> 
> ```bash
> # echo "KEYFILE_PATTERN=/etc/luks/*.keyfile" >>
> /etc/cryptsetup-initramfs/conf-hook
> # echo "UMASK=0077" >> /etc/initramfs-tools/initramfs.conf
> ```
> 
> - Create a randomised key-file of 4096 bits (512 bytes), secure it, and
> add it to the LUKS volumes (Man-pages for dd chmod):
> 
> ```bash
> # mkdir /etc/luks
> # dd if=/dev/urandom of=/etc/luks/boot_os.keyfile bs=512 count=1
> 1+0 records in u=rx,go-rwx /etc/luks
> 1+0 records out
> 512 bytes (0.5 kB, 0.5 KiB) copied, 0.0002368 s, 17.3 MB/s
> 
> # chmod u=rx,go-rwx /etc/luks
> # chmod u=r,go-rwx /etc/luks/boot_os.keyfile
> 
> # cryptsetup luksAddKey /dev/nvme0n1p1 /etc/luks/boot_os.keyfile
> Enter any existing passphrase:
> 
> # cryptsetup luksAddKey /dev/nvme0n1p5 /etc/luks/boot_os.keyfile
> Enter any existing passphrase:
> ```
> 
> Add the keys to the crypttab:
> 
> ```bash
> # echo "LUKS_BOOT UUID=$(blkid -s UUID -o value ${DEVP}1)
> /etc/luks/boot_os.keyfile luks,discard" >> /etc/crypttab
> # echo "${DM}5_crypt UUID=$(blkid -s UUID -o value ${DEVP}5)
> /etc/luks/boot_os.keyfile luks,discard" >> /etc/crypttab
> ```
> 
> The above is taken from: [Full_Disk_Encryption_Howto_2019 - Community
> Help
> Wiki](https://help.ubuntu.com/community/Full_Disk_Encryption_Howto_2019#Post-Installation_Steps)
> 
> ---
> 
> # Issue
> 
> The boot partition unlocks very quickly (5 seconds) but the LVM volume
> takes about 6 minutes to unlock.
> 
> Following are the key dump of both these partitions. With the keyslot 0
> in both being the same passphrase, and keyslot 1 being the key file:
> 
> ```
> $ sudo cryptsetup luksDump /dev/nvme0n1p1
> Place your right index finger on the fingerprint reader
> LUKS header information for /dev/nvme0n1p1
> 
> Version:        1
> Cipher name:    aes
> Cipher mode:    xts-plain64
> Hash spec:      sha256
> Payload offset: 4096
> MK bits:        512
> MK digest:      ec 22 27 de c1 ef 40 0f a5 cf 37 d3 96 5c d5 b2 6e c8 dd 90
> MK salt:        62 1a 05 81 ba 60 3b 0d b1 8a 9f f0 04 98 27 54
>                   06 b6 8d 72 53 23 09 47 ea 5f 80 1d d7 c5 ca 50
> MK iterations:  305173
> UUID:           586de9a0-14c7-40d7-b721-7fdba2e3b184
> 
> Key Slot 0: ENABLED
>           Iterations:             1000
>           Salt:                   4b f1 99 85 84 a5 00 d6 a4 e8 e1 07 35
> b4 da a1
>                                   fc 97 59 5f 4c f8 e1 9b 49 71 29 af e5
> 56 b1 19
>           Key material offset:    8
>           AF stripes:             4000
> Key Slot 1: ENABLED
>           Iterations:             4848906
>           Salt:                   91 70 85 49 f3 31 e8 53 1f 39 aa 6d 7a
> 3e 84 de
>                                   e4 3f bd 3d 65 bf f6 b1 e6 8c 15 fa 34
> b9 e3 e0
>           Key material offset:    512
>           AF stripes:             4000
> ```
> 
> ```
> $ sudo cryptsetup luksDump /dev/nvme0n1p5
> LUKS header information
> Version:        2
> Epoch:          10
> Metadata area:  16384 [bytes]
> Keyslots area:  16744448 [bytes]
> UUID:           ee8854e8-54f6-4f7b-b326-02fdee357d0e
> Label:          (no label)
> Subsystem:      (no subsystem)
> Flags:          (no flags)
> 
> Data segments:
>     0: crypt
>           offset: 16777216 [bytes]
>           length: (whole device)
>           cipher: aes-xts-plain64
>           sector: 512 [bytes]
> 
> Keyslots:
>     0: luks2
>           Key:        512 bits
>           Priority:   normal
>           Cipher:     aes-xts-plain64
>           Cipher key: 512 bits
>           PBKDF:      argon2id
>           Time cost:  1000
                         ^^^^
This is insane value for argon2 and it would explain your 6 minutes 
unlock time. Usually on my 2 years old laptop I get values in range 6-9 
iterations (Time cost) with 4 threads and 1GiB ram used when I let 
cryptsetup do the benchmark with default target time ~2 seconds. Are you 
sure you did not add --pbkdf-force-iterations parameter in your 
luksAddKey command earlier?

With regards
O.