I was able to expand initrd-plymouth.img using 'zcat initrd-plymouth.img | cpio -iv', but still no luck. I can't find the key file in the resulting directory tree. Do you know what it's called? I've looked for files with the strings "key", "cred", "pass", and "crypt".
By the way, the only relevant files I see on the mounted boot partition are initramfs* and initrd-plymouth.img. I'm assuming the initrd is initrd-plymouth.img.
Also, when I mount the second partition (/boot/efi), it's empty. Is this expected?
Thanks!