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File Encryption and VIM
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You can create a new vim encrypted file using

  vim -x filename

or while editing a file you use

  :X

vim will write that file using the key it asks for in encrypted form.

The key is saved during the editing using the "key" setting, and it will
not show the key's value if asked.

No password verification is used, so if the wrong password is used you will
see binary garbage on the screen. If this is edited and saved it will corrupt
the file from the point of edit.

To remove the encryption from a vim encrypted file use the command

 :set key=

The file will have file magic of "VimCrypt~" but no special suffixes.
The file magic insures that if vim edits the file, it will ask the
user for a password to decrypt it for editing.


The method by default is 'zip' which is weak. You can change the default to
a stronger method using   "set cm=blowfish" in your ".vimrc" file while a file
is in memory the files encryption method can be changed using ":setlocal
cm=blowfish" otherwise it is the same as the encryption used when reading.

The encryption method is stored as byte 9 and 10 with the string values
of "01" or "02" respectivally.

****
Other than this the actual encryption method is not known at this time.
So without further research I would not be able to decrypt a vim encryted
file with out using vim.
****

WARNING: While restore and undo files are encrypted the viminfo file is
not.  Any command history or buffers may be saved into the viminfo file
including cut/paste buffers, and ":set key=..." commands.

No method of specifying an external encryption program is provided.

IN SUMMARY: I do not recommend using vim built-in encryption.

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Using an External Program (DIY)

You can also directly edit a file encrypted using an external program.

For example, using "encrypt" and "encrypt -d" respectivally, for files
with a ".enc" suffix...  (you could use file magic too)

======8<--------CUT HERE----------axes/crowbars permitted---------------
"
" Allow direct editing of Encrypted files
"
set nocompatible        " Use Vim defaults like multi-undo (much better!)

" Decrypt/Encrypt a ".kpt", openssl encryted file, using "keepout"
" using a PBKDF v2 (salt+count) aes-256-cbc encryption variant.
"
augroup enc
autocmd!
autocmd  BufReadPre,FileReadPre     *.enc setlocal binary
autocmd  BufReadPre,FileReadPre     *.enc set history=0 cmdheight=3
autocmd  BufReadPre,FileReadPre     *.enc set noundofile noswapfile
autocmd  BufReadPre,FileReadPre     *.enc set nowritebackup viminfo=
autocmd  BufReadPre,FileReadPre     *.enc set encoding=utf-8 fileencoding=utf-8

autocmd  BufReadPost,FileReadPost   *.enc set shell=/bin/sh shellredir=>
autocmd  BufReadPost,FileReadPost   *.enc '[,']!keepout -d
autocmd  BufReadPost,FileReadPost   *.enc set nobinary cmdheight& shell&
autocmd  BufReadPost,FileReadPost   *.enc exe "doau BufReadPost ".expand("%:r")
autocmd  BufReadPost,FileReadPost   *.enc redraw!
"
autocmd  BufWritePre,FileWritePre   *.enc mark z
autocmd  BufWritePre,FileWritePre   *.enc set binary cmdheight=3 shell=/bin/sh
autocmd  BufWritePre,FileWritePre   *.enc '[,']!keepout
"
autocmd  BufWritePost,FileWritePost *.enc silent undo
autocmd  BufWritePost,FileWritePost *.enc setlocal nobinary
autocmd  BufWritePost,FileWritePost *.enc set cmdheight& shell&
autocmd  BufWritePost,FileWritePost *.enc 'z
augroup END

======8<--------CUT HERE----------axes/crowbars permitted---------------

The encrypted file as it is only decrypted in the editors buffer in memory.

An example "encrypt" command is available in
  https://antofthy.gitlab.io/software/#encrypt

This however has been superseeded by the "keepout" shell script
  https://antofthy.gitlab.io/software/#keepout

You can see the full vim auto-commands I use with these, as well as for pgp,
gpg, gzip, and others in...
  https://antofthy.gitlab.io/software/#encrypt.vim

PS: GZipping text files before encryption is a good way to make them smaller.
but is an extra step.

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