i would expect an hex editor mode would make much more sense to be added before they went to such shenanigans feature such as frivolous encryption. which can be trivial to use the Unix way... the way hex editing must be done for great pains btw.
I would argue that, encryption, if implemented properly, is best integrated into the editor because the editor can be sure to store the clear text in mlock'd memory and avoid leaking clear text in other ways (such as into ~/.viminfo). If you have to decrypt with a separate tool, the clear text hits the disk and the editor doesn't know to be careful with it. These are concerns that aren't present with hex editing.
I have no idea if vim is this careful though and sadly I wouldn't count it.
Cleartext doesn't have to be saved to disk for a separate tool to be used. You can pretty much use GPG from vim as-is just by piping the buffer through it: ":%!gpg -e -a -r yourself" and ":%!gpg -d". The vim GPG plugins can take care of the remaining annoyances.
The UX for vim's encryption is really good - it's convenient and easy to use. Any replacement would need to be equally easy and well-integrated. If you require users to do manual steps, like type commands or remember to tell vim that it's editing sensitive content, then mistakes will be made that harm security. If the plugin interface can provide a sufficient level of integration, that's great and would be a good alternative to building crypto into vim itself.
They all support general disk/filesystem encryption, too. If you're technically minded enough to be using vim and trying to encrypt files with it, and you're not using an encrypted filesystem to start with, you're pretty nuts.
The core UX for gnupg.vim is open .gpg/.pgp/.asc file, be automatically prompted for passphrase (unless file is new), edit file, save (be prompted for recipients if new). Done.
You're obviously going to have to complain to the vim maintainers about sensitive content. There's been a patch floating around for over a decade to get vim to support mlock. Its blowfish encryption is certainly no safer than gnupg.vim in that regard. gnupg.vim does turn off the viminfo/swapfile/undofile functionality.
> gnupg.vim does turn off the viminfo/swapfile/undofile functionality.
Thanks. That is excellent UX and knowing that I can agree it's what people should use instead of the built-in encryption.
Edit: Actually just use gnupg.vim - as nknighthb has explained the UX is just as good as vim's builtin encryption, and then you don't have to worry that this whole thread about vim's builtin encryption was predicated with "...if implemented properly...", which you certainly can't take for granted.
Like TFA says, don't roll your own crypto. GnuPG exists for a reason.
http://iacr.org/archive/fse2007/45930168/45930168.pdf
And of course there's ciphertext malleability attacks as it's not using authenticated encryption