This is how I managed to shrink an encrypted LUKS volume with ext4 filesystem on Linux

1. backup data (seriously)

2. overshrink the ext4 filesystem by a few more GB than needed

   • cryptsetup luksOpen /dev/sdc1 edata
   • umount /dev/mapper/edata
   • e2fsck -f /dev/mapper/edata
   • resize2fs -p /dev/mapper/edata 300G
3. cryptsetup luksClose edata
4. truncate LUKS volume using fdisk or gdisk to e.g. 320 GB
5. cryptsetup luksOpen /dev/sdc1 edata
6. grow the ext4 filesystem back to 100 %