Correct. But we're talking about two different definitions here.
If the same ASN.1 statement can lead to two legal encodings,
the encoding is not 'distinguished' in the sense of DER.
It is not the same ASN.1 statement.
I also don't see the
difference (with respect to DER) between the DEFAULT notation which is
addressed
by DER and the OPTIONAL notation which is not.
There's a vital distinction between the two. The DEFAULT notation is
constrained to not have any semantics associated with it -- the presence of a
value that equals the default versus the value not being there so the default
applies are defined to have identical semantics. But this does not apply to an
OPTIONAL sequence. The presence of an empty sequence versus the omission of
the
sequence can be semantically distinct.
OK, I understand this. My problem was that I considered the SEQUENCE ...
OPTIONAL
as one ASN.1 definition, but in fact it's two, one with the element being
present,
and one with the element being absent. The two possible semantics should not be
eliminated through DER. Fine.
Ned
Wolfgang