Version 1.9 adds TrueCrypt keyfile support to Disk Decipher. If you need keyfile support for other disk formats (FreeOTFE, LUKS) let me know so I can add it to my todo list.
To use a keyfile, the keyfile first needs to be imported into Disk Decipher.
Importing a keyfile
To transfer your keyfile encrypted to Disk Decipher, store the keyfile inside a TrueCrypt container and open it inside Disk Decipher. After opening the keyfile in Disk Decipher, tap the action button and select "Import keyfile".
Disk Decipher uses the iOS keychain to store the keyfile. TrueCrypt keyfiles are hashed using the TrueCrypt keyfile algorithm, the resulting 512-bit hash is stored in the iOS keychain.
Using a keyfile
After importing a keyfile, you can use the keyfile by simply selecting it when mounting a TrueCrypt container.
Deleting a keyfile
If you want to delete a keyfile from Disk Decipher, simply swipe from left to right on the keyfile you want to delete, and tap the Delete button that is presented. The keyfile will be deleted from the iOS keychain.