From: Jeffrey Hutzelman [mailto:jhutz(_at_)cmu(_dot_)edu]
It's a subset, in fact. All DER is valid BER.
It is an illogical subset defined in a throwaway comment in an obscure part of
the spec.
A subset is not necessarily a reduction in complexity. Let us imagine that we
have a spec that allows you to choose between three modes of transport to get
to school: walk, bicycle or unicycle.
The unicycle option does not create any real difficulty for you since you
simply ignore it and use one of the sensible options. And it is no more complex
to support since a bicycle track can also be used by unicyclists.
Now the same derranged loons who wrote the DER encoding decide that your
Distinguished transport option is going to be unicycle, that is all you are
going to be allowed to do.
Suddenly the option which you could ignore as illogical and irrelevant has
become an obligation. And that is what DER encoding does.
Since you don't appear to have coded DER encoding I suggest you try it before
further pontification. If you have coded it and don't understand how so many
people get it wrong then you are beyond hope.
BTW its not just the use of definite length tags, there is also a requirement
to sort the content of sets which is a real fun thing to do. Particularly when
the spec fails to explain what is actually to be sorted.
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