The description for the USE flag "crypt" states "Add support for encryption -- using mcrypt or gpg where applicable", however, many instances of the crypt USE flag do not relate to gpg or mcrypt. However, this is not the main concern. In particular, the crypt use flag for util-linux actually applies a third-party patch for loop-AES -- while loop-AES is a rarely used out-of-tree kernel module, not endorsed by the Linux kernel developers, Gentoo, nor any other major distributions. I would expect such generic USE flags like "crypt" to only add visible dependencies, or apply patches which have a wide support and user base -- but certainly not apply obscure patches to core packages and pass without user's notice. This patch is only really necessary when the user explicitly knows that he's using loop-AES; I'd suggest renaming the flag "loopaes" or whatnot.
it's more historical. when the kernel/util-linux lacked any encryption support, USE=crypt pulled into cryptographically features. things have since changed though, so updating the USE flag makes sense.
latest versions have been converted to USE=loop-aes
