I recently stumbled on this blog post covering how to transparently encrypt and de-crypt *.gpg files:
http://blog.endpoint.com/2012/05/vim-working-with-encryption.html
The gist is to add this to your .vimrc file:
" Transparent editing of gpg encrypted files.
" By Wouter Hanegraaff
" see: http://blog.endpoint.com/2012/05/vim-working-with-encryption.html
"
augroup encrypted
au!
" First make sure nothing is written to ~/.viminfo while editing
" an encrypted file.
autocmd BufReadPre,FileReadPre *.gpg set viminfo=
" We don't want a swap file, as it writes unencrypted data to disk
autocmd BufReadPre,FileReadPre *.gpg set noswapfile
" Switch to binary mode to read the encrypted file
autocmd BufReadPre,FileReadPre *.gpg set bin
autocmd BufReadPre,FileReadPre *.gpg let ch_save = &ch|set ch=2
" (If you use tcsh, you may need to alter this line.)
autocmd BufReadPost,FileReadPost *.gpg '[,']!gpg --decrypt 2> /dev/null
" Switch to normal mode for editing
autocmd BufReadPost,FileReadPost *.gpg set nobin
autocmd BufReadPost,FileReadPost *.gpg let &ch = ch_save|unlet ch_save
autocmd BufReadPost,FileReadPost *.gpg execute ":doautocmd BufReadPost " . expand("%:r")
" Convert all text to encrypted text before writing
" (If you use tcsh, you may need to alter this line.)
autocmd BufWritePre,FileWritePre *.gpg '[,']!gpg --default-recipient-self -ae 2>/dev/null
" Undo the encryption so we are back in the normal text, directly
" after the file has been written.
autocmd BufWritePost,FileWritePost *.gpg u
augroup END