It has sys-apps/util-linux[loop-aes] as DEPEND. The higher stable that satisfies that requirement is sys-apps/util-linux-2.20.1-r2, because the latest stable doesn't have loop-aes IUSE.
Created attachment 332416 [details, diff] Return loop-aes functionality to util-linux 2.21.2 and 2.22.1 There are patches for util-linux 2.21.2 and 2.22.1 in loop-AES-3.6g.tar.bz2. They're newer than the patches at <http://loop-aes.sourceforge.net/updates/>, and work for me.
(In reply to comment #1) IUSE is sorted. keep it that way. loop-aes patches don't go in $FILESDIR -- they are way too big.
Vicente: Please try to use the new app-crypt/loop-aes-losetup[1]. [1] http://article.gmane.org/gmane.linux.gentoo.user/262981