Hi

It looks like you'll have to modify CBC.pm. In my version (2.14), the 'finish' method deletes the current IV.

    delete $self->{'civ'};
    delete $self->{'buffer'};
    return $result;
}
[download]

You'll have to prevent that from happening, and then add a method to return the current (last) IV, instead of the initial IV

sub get_civ
{
 return $self->{civ};
}
[download]

I have no idea if or how this affects the security of the two messages.

Hope this helps, J