crypt-file-client.js

<input type='file' accept='*' onchange='openFile(event)'><br>
<textarea id='output' rows=9 cols=35></textarea>

<script>

  var openFile = function(event) {

    var output = document.getElementById('output');
    var input = event.target;
   
    var reader = new FileReader();

    reader.onload = function(){

      var dataText = reader.result;

      output.value = dataText
      
      encryptText(dataText, "senha1224").
      then(buffCry => {

        console.log(buffCry); 
        output.value += "\n\ncrypt:\n" + ab2str(buffCry);

      } , err =>  { 
        output.value += "\n\ncrypt:\n" + err 
      });
    };

    // reader.readAsArrayBuffer(input.files[0]);

    reader.readAsBinaryString(input.files[0]);

  };
  
  const encryptText = async (plainText, password) => {

    const ptUtf8 = new TextEncoder().encode(plainText);

    const pwUtf8 = new TextEncoder().encode(password);
    const pwHash = await crypto.subtle.digest('SHA-256', pwUtf8); 

    const iv = crypto.getRandomValues(new Uint8Array(12));
    const alg = { name: 'AES-GCM', iv: iv };
    const key = await crypto.subtle.importKey('raw', pwHash, alg, false, ['encrypt']);

    return crypto.subtle.encrypt(alg, key, ptUtf8);
}

function ab2str(buf) {
  
  return String.fromCharCode.apply(null, new Uint8Array(buf));
}

function str2ab(str) {

  var buf = new ArrayBuffer(str.length*2); // 2 bytes for each char
  var bufView = new Uint16Array(buf);
  for (var i=0, strLen=str.length; i < strLen; i++) {
    bufView[i] = str.charCodeAt(i);
  }

  return buf;
}

</script>