TO: >INTERNET pem-dev(_at_)tis(_dot_)com
Both X9 and X12 standards assume that IV's are best encrypted.
The reason (as I recall) was that the first part of messages
would be the most likely to be repeated from one message to the
next. An unexpected IV would help to prevent a known plaintext
attack, since text further from the front of the message is less
likely to be known.
The reason that this is true for business messages is that there
is a fair bit of structural information that will not change from
one message to another.
Peace
Tom Jones - Lemcom