Boot on LUKS drive ( Rapsberry pi 4 )

Hi,

The SBC Raspberry Pi 4 boot on an sdcard with two partition /boot and /

So I managed to encrypt the partition / with cryptsetup

Here the partition of my sd-card

device	FILESYS	LABEL	UUID
sdb1	vfat	BOOT	( 9 characters )
sdb2	crrypto_LUKS		( 36 characters )

I've modified the /boot/cmdline.txt

to ( on one line )

console=serial0,115200
console=tty1
root=UUID=#If I try the UUID of sdb2 it fail and also the UUID when I use `cryptsetup luksOpen /dev/sdb2 b2open`
rootfstype=ext4
fsck.repair=yes
loglevel=5
net.ifnames=0
firmware_class.path=/lib/firmware/updates/brcm
rootwait
cryptdevice=UUID=#I dont know which one:b2open

any ideas ?

Thanks.