When creating the DES cipher object with DES.new, we use the property
card_keys.dek. This property may hold a 16 byte key, but DES uses
an 8 byte key (56 bit + 8 bit integrity). Pycryptodome does not
automatically ignore excess key bytes. Instead it throws an
exception. This means we need to make sure to supply only the first
8 bytes of card_keys.dek
See also: https://pycryptodome.readthedocs.io/en/latest/src/cipher/des.html
Related: OS#6531
Change-Id: I92e0dc6a6196b532bd8b53fca7b9e78070d6903f
c595221bc3