We have the the 'crypt' use flag to enable cryptography support. You're unneedlessly raising the complexity of portage by adding weird named use flags like "on-the-fly-crypt".
You can read ChangeLogs? If so, please do so.
I admit I didn't. But I hope this is only a workaround in the meantime. It can't be the solution to end with thousands of different use flags. Personally I start to dislike Gentoo a bit because of the number of use flags. It's becoming more painful than helpful.
I also disliked to change the USE-flag from 'crypt' to 'on-the-fly-crypt'. But this patch will never-ever work on all Linux-arches and not on any non-Linux-system for sure. A solution would be to drop that patch again.
Hm, then it's probably time to enhance portage to accept a list of use.mask'ed packages after the use flag itself.
That's not my area of development. You should address this bug to the portage-herd.
Right. >> Bug 98996