Ok, going from memory here cause I'm not in front of our implementation code
or a copy of the spec so if I'm wrong Murray and/or Mike will correct me:
Does the above mean the empty tag "b=;" is used or none?
Yes, use b=;
Is there a CRLF added to the body when the "DKIM-Signature:" is
added after the body?
There's no CRLF after the DKIM-Signature: that you append to the end of the
body. But there is a CRLF between the end of the body and the start of the
DKIM-Signature. This is probably what's throwing you as we came across this
several times.
For example:
Last line of message body<CRLF>
<CRLF>
DKIM-Signature: <whatever>
--
Arvel