How do I use Sha256 on a file(binary file such as images) in javascript?

Question

I am trying to do a Sha256 on a file in Javascript. I used FileReader(HTML5) to read in a file. I use the readAsBinaryString function in the FileReader to pass in the images file. Then on the FileReader.onload function I pass in the evt.target.result to the SHA256 method in the CryptoJs API. I am able to successfully get a hash value but it is not correct. When I pass in a text file, it works fine but not image file.

Code(Should be able to copy the code below to a HTML file and run it on firefox - press the "entire file" button):

<style>
  #byte_content {
    margin: 5px 0;
    max-height: 100px;
    overflow-y: auto;
    overflow-x: hidden;
  }
  #byte_range { margin-top: 5px; }
</style>

<input type="file" id="files" name="file" /> Read bytes: 
<span class="readBytesButtons">
  <button data-startbyte="0" data-endbyte="4">1-5</button>
  <button data-startbyte="5" data-endbyte="14">6-15</button>
  <button data-startbyte="6" data-endbyte="7">7-8</button>
  <button>entire file</button>
</span>
<div id="byte_range"></div><BR>
<div id="byte_content"></div><BR>
<div id="crypto_sha256"></div>

<script src="http://crypto-js.googlecode.com/svn/tags/3.0.2/build/rollups/sha256.js"></script>
<script src="http://crypto-js.googlecode.com/svn/tags/3.0.2/build/components/enc-base64-min.js"></script>
<script>

  var sha256;

  function readBlob(opt_startByte, opt_stopByte) {

    var files = document.getElementById('files').files;
    if (!files.length) {
      alert('Please select a file!');
      return;
    }

    var file = files[0];
    var start = parseInt(opt_startByte) || 0;
    var stop = parseInt(opt_stopByte) || file.size - 1;

    var reader = new FileReader();

    // If we use onloadend, we need to check the readyState.
    reader.onloadend = function(evt) {
      if (evt.target.readyState == FileReader.DONE) { // DONE == 2
        document.getElementById('byte_content').textContent = evt.target.result;
        document.getElementById('byte_range').textContent = 
            ['Read bytes: ', start + 1, ' - ', stop + 1,
             ' of ', file.size, ' byte file'].join('');

        //**UPDATED SOLUTION: Since its binary data, the message needs to be converted from string to bytes using Latin1**
            sha256.update(CryptoJS.enc.Latin1.parse(evt.target.result));

        var hash = sha256.finalize();

        document.getElementById('crypto_sha256').textContent = ['SHA-256: ', hash].join('');
      }
    };

    var blob = file.slice(start, stop + 1);
    reader.readAsBinaryString(blob);
  }

  document.querySelector('.readBytesButtons').addEventListener('click', function(evt) {
    if (evt.target.tagName.toLowerCase() == 'button') {
      var startByte = evt.target.getAttribute('data-startbyte');
      var endByte = evt.target.getAttribute('data-endbyte');

      sha256 = CryptoJS.algo.SHA256.create();

      readBlob(startByte, endByte);
    }
  }, false);
</script>

Sample outputs:

1. Testing a "text" file:

   • SHA256 generated by Javascript:
     78cb5e86455dc8e3bc20fe17e0213a938281216d57b31f8307f5bca67c37bb09
   • SHA256 generated by cygwin on the same file:
     $ sha256sum Phillips.txt 78cb5e86455dc8e3bc20fe17e0213a938281216d57b31f8307f5bca67c37bb09 *SomeTestFile.txt

2. Testing a "binary" file(pdf):

   • SHA256 generated by Javascript:
     57f93c1d20a8ad8ade984a1d9756c1a40600bd8a7527601945c4e0b5e042c605
   • SHA256 generated by cygwin on the same file:
     $ sha256sum Smoke\ Detector\ Brochure.pdf 57f93c1d20a8ad8ade984a1d9756c1a40600bd8a7527601945c4e0b5e042c605 *Smoke Detector Brochure.pdf

Answer 1

I know this question is quite old but I figured I'd share what I know anyways.

You can do this more easily by doing what I discuss in this answer https://stackoverflow.com/a/17848266/2226207

Basically you can include components/lib-typedarrays-min.js and then do the following in code.

var reader = new FileReader();

// If we use onloadend, we need to check the readyState.
reader.onloadend = function(evt) {
  if (evt.target.readyState == FileReader.DONE) { // DONE == 2

    var wordArray = CryptoJS.lib.WordArray.create(e.target.result);
    var hash = CryptoJS.SHA256(wordArray);
  }
};

var blob = file.slice(start, stop + 1);
reader.readAsArrayBuffer(blob);

I haven't tested the above solution but it should work fine.