The key must be specified in base 36. Only digits 0-9 and letters a-z can be used when specifying the key. Each of the four ...

The key must be specified in base 36.  Only digits 0-9 and letters a-z can be
used when specifying the key.  Each of the four 64 bit key chunks may be
specified with up to 13 characters and must be separated by a period. None of
the key chunks can be zero.  1.1.1.1, 1.2.3.4, theprevious.keys.arenot.secure,
automatically.generated.keysare.safer4you are all examples of valid keys.
Run "bcdedit -dbgsettings /?" for command line assistance.