I have an embedded Linux system with unencrypted kernel image and initramfs in NAND flash.My RootFS is in SD card.I want to encrypted some files on SD Card as my SD card is easily accessible physically.For this I am planing to use eCryptfs.But I want to keep the keys inside NAND flash in kernel image or initramfs.What are my options, what is best way to secure some files on my SD card.  
eCryptfs key in kernel image or initramfs
kernel;boot;encryption;initramfs;ecryptfs