When I bumped to 0.81b after running 0.77 for awhile, I did a deep check on my roms. In all they seem to work, but most of my diskimages pops up with the following error; "no SHA1 set; better convert chd to new standard"

Now, I have tried to fill my knowledge about this by searching on google.com, the documentation and forums etc, but I aint getting any smarter (and I rarely ask for help unless I am 100% I cant find the information elsewhere).

My questions are basicly:
1. Is it possible to convert CHD to SHA1
2. What do I need to do?