• If you suspect that a partition requires a keyfile instead of a passphrase to open check the file:

cat /etc/crypttab

• A line like this will indicated such situation:

shirka_ssd-cache-decrypted UUID=43xxxca6-xxxx-xxxx-xxxx-062a3cc5acee crypt.key luks,discard

• To open such partition use the following command:

cryptsetup -d crypt.key luksOpen /dev/bcache0 shirka-bcache0-uncrypt

• To show existing associated keyslots in the partition:

sudo cryptsetup luksDump /dev/bcache0