Encrypt static HTML with Ruby and CryptoJS.

decrypt.js

var payload = "{{ content | encrypt_data }}".split("|"); //content via Ruby

var iv         = payload[0]
    hmac       = payload[1],
    cipherText = payload[2];

//CryptoJS keeps all objects as WordArrays, so you have to coerce as strings at times.

//Only get passphrase via input or cookie, convert to sha256 hex digest
//echo -n "passphrase" | openssl dgst -sha256
//(In El Capitan, may need to run a sudo)
//var passphraseDgst = CryptoJS.SHA256("passphrase").toString();
var key = passphraseDgst;

//compare above passphrase with HMAC signature of data (to see if key is the right one)
var decryptedhmac = CryptoJS.HmacSHA256(cipherText, CryptoJS.enc.Hex.parse(passphraseDgst)).toString().trim();

//If they match...
if(CryptoJS.enc.Base64.parse(hmac).toString() === decryptedhmac){
  
  //decrypt based on key (passphrase) and iv
  var decrypted = CryptoJS.AES.decrypt(
    {ciphertext:CryptoJS.enc.Base64.parse(cipherText)},
    CryptoJS.enc.Hex.parse(passphraseDgst),
    {iv:CryptoJS.enc.Base64.parse(iv)}
  );
  
  var html = CryptoJS.enc.Utf8.stringify(decrypted);//do something with html
}

encrypt.rb

def encrypt_data(input)
  digest = Digest::SHA256.new
  digest.update("passphrase")
  key = digest.digest

  cipher = OpenSSL::Cipher::AES256.new(:CBC)
  cipher.encrypt
  cipher.key = key
  cipher.iv = iv = cipher.random_iv

  encrypted = cipher.update(input) + cipher.final
  encoded_msg = Base64.encode64(encrypted).gsub(/\n/, '')
  encoded_iv = Base64.encode64(iv).gsub(/\n/, '')

  hmac = Base64.encode64(OpenSSL::HMAC.digest('sha256', key, encoded_msg)).strip
  "#{encoded_iv}|#{hmac}|#{encoded_msg}"
end

index.html

<!-- https://code.google.com/archive/p/crypto-js/ -->
<script src="js/rollups/aes.js"></script>
<script src="js/rollups/sha256-min.js"></script>
<script src="js/rollups/hmac-sha256.js"></script>

<script src="decrypt.js"></script>