[root@localhost ~]# touch /tmp/uuu
[root@localhost ~]# chmod 400 /tmp/uuu
[root@localhost ~]# ls -al /tmp/uuu
-r--------. 1 root root 475 Mar  8 09:54 /tmp/uuu
[root@localhost ~]# dd if=/dev/random bs=512 count=4 2>/dev/null | base64 | dd of=/tmp/uuu 
0+1 records in
0+1 records out
475 bytes copied, 0.0949688 s, 5.0 kB/s
[root@localhost ~]# cat /tmp/uuu
6eIVx5K2CdvIMO/5JSrD2JEit9mJjUj+4jw8TxDJtuwPKVCRgJppldjZ/51h6tFris/+DxK/BBJS
pKziup0SK1XpP3704mZgKwnl+9/lR0rdOmD4uItekgadAV+7mDknyYF5Jz1BR5dgeOHD7ACLb3bi
MrpZoXrxE6IISEzz88LeJQAxBZMNtGMUHfpW7pElngSVWjZHoqAMDLTFj/tx+3VZslhWFrDeRJc4
quZmPLLMrK+ucHxRzBR3n9REFyn6OYRXplQoizPIjV9wNRe0BREh4fpmKYh9uMZtre1kJt99Jd3W
zgoo15VWi44c47YyvDY86VPMOJIuiEoArNP6DMhzvd2j5GOpdCQsmIyecvRdPEexX5mLUSfWCeWc
fITqtooI+Sg6d3K4kgQMrDIPip16YkrXyPcKz2OgLCFUDSMqUcf4+R0LACQ9fdQidGLH+SFDft1M
cLei89Bg93Vl
[root@localhost ~]# cat /proc/version 
Linux version 4.18.0-80.el8.x86_64 (mockbuild@kbuilder.bsys.centos.org) (gcc version 8.2.1 20180905 (Red Hat 8.2.1-3) (GCC)) #1 SMP Tue Jun 4 09:19:46 UTC 2019
[root@localhost ~]# 

        device="/dev/md0"
        sed -i 's/none luks,discard/\/crypto_keyfile.bin luks,keyscript=\/bin\/cat/g' /etc/crypttab
        dd bs=512 count=4 if=/dev/random of=/crypto_keyfile.bin
        chmod 400 /crypto_keyfile.bin
        cryptsetup luksChangeKey $device -S 0 /crypto_keyfile.bin
        echo "#!/bin/bash
        cp /crypto_keyfile.bin \"\${DESTDIR}\"" > /etc/initramfs-tools/hooks/crypto_keyfile.sh
        chmod +x /etc/initramfs-tools/hooks/crypto_keyfile.sh