How to create a LUKS partition encrypted with Adiantum, ideal for low end and older devices/computers

adiantum-encryption-how-to.md

How to create a LUKS partition encrypted with the Adiantum scheme

Important note

• Sector size and key size are fixed, you cannot change them!
• You can play with the hash but using less than sha256 is irresponsible!
• You can convert an already existing luks2 partition with cryptsetup(8).

Very low end devices or computers (say, an old Pentium, Celeron, Raspberry Pi or older SoC)

cryptsetup luksFormat --type luks2 \
--sector-size 4096 \
--cipher xchacha12,aes-adiantum-plain64 \
--hash sha256 --key-size 256 <device>

cryptsetup reencrypt \
--sector-size=4096 \
--cipher xchacha12,aes-adiantum-plain64 \
--hash sha256 --key-size 256 <device>

Low end devices or computers (say, a Core 2 Duo, a smartphone post 2016)

cryptsetup luksFormat --type luks2 \
--sector-size 4096 \
--cipher xchacha20,aes-adiantum-plain64 \
--hash sha256 --key-size 256 <device>

cryptsetup reencrypt \
--sector-size=4096 \
--cipher xchacha20,aes-adiantum-plain64 \
--hash sha256 --key-size 256 <device>

No need to differentiate as xchacha12 is (for now) known to be as safe, has plenty of margins. Might as well be faster.

I see that you specify a sector size of 4096. Isn't it only suitable for those disks that use 4k-sized sectors? For example, mine reports only 512.

After fiddling with sector alignment to make the size of a partition (in sectors) a multiple of 8, cryptsetup is able to encrypt in 4k. While it seems to work, and the partition is later formatted and mounted without any noticeable issues, I wonder if this is really a good idea. I still get some warnings when I run fdisk -l (on Alpine Linux):

Disk /dev/dm-0: 58 GB, 61973987328 bytes, 121042944 sectors
941 cylinders, 255 heads, 63 sectors/track
Units: sectors of 1 * 4096 = 4096 bytes

Disk /dev/dm-0 doesn't contain a valid partition table
Note: sector size is 4096 (not 512)

CORRECTION: The error above is also happening with a sector size of 512, so it's not related to 4k sector size.