This property allows or forbids the use of ASN.1 tags of undefined size.
Set UseUndefSize to
False to prevent use of ASN.1 tags with undefined size.
Usually PKCS#7 messages are handled correctly when such tags are used.
However some ASN.1 parsers (S/MIME handler in Outlook Express, security plugins of Adobe Acrobat) can't correctly
handle such tags. If you are targeting such software, you need this property.
Default value is True (use of such tags is allowed).