I do not know anything about protected kepubs, since I do not have one. But from Davidfor's
Quote:
The title can be seen as it is in a file that is stored without encryption
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I jump to the conclusion that the OPF file is not encrypted. There you can verify whether it is an epub 3 (package version="3.0"). However, calibre can handle epub 3, so that should not make a difference.
Most decisive advantage of epub 3 over epub 2 for Japanese texts seems to be vertical writing. It shows also furigana, I cannot recall whether epub 2 did this already.