Hmac.vim is a project mainly written in Vim Script, it's free.
hmac() function
This is a mirror of http://www.vim.org/scripts/script.php?script_id=2972
This is a port of rfc 2104 hmac function.
hmac#md5(key, text) require vimscript#2806 hmac#sha1(key, text) require vimscript#2971