为什么使用crypto-js为不同的pdf文件获得相同的哈希值？

Question

I upload a pdf file and use crypto-js to create a hash from it, but I always get the same hash no matter which file I upload. Also, the hash I get does not correspond to the hash I get from the file when I use an online tool to create the hash. I have the same issue with txt files and if I load the files from the assets directory. I also tried other libraries and have the same issue.

What I'm I missing?

I use Angular 6. Here is how I do it.

import { Component } from '@angular/core';
import sha256 from 'crypto-js/sha256';

@Component({
  selector: 'ct-sign-page',
  templateUrl: './sign-page.component.html',
  styles: []
})
export class SignPageComponent {
  public file: File;

  public fileChange(event): void {
    this.file = event.target.files[0];
    const hash = sha256(this.file);
    console.log(hash.toString());
  }
}

Update: This is what I get if I log this.file before I create the hash.

File
lastModified: 1603727900290
lastModifiedDate: Mon Oct 26 2020 16:58:20 GMT+0100 (Central European Standard Time) {}
name: "sample.pdf"
size: 3028
type: "application/pdf"
webkitRelativePath: ""
__proto__: File

Answer 1

You can use FileReader to read the file and create a hash based on its content.

Though I'm not sure why it is generating the same hash but I guess it is related to some internal methods like toString() which return same string for any event.target.files[0] .

 fileChange = (event) => { var file = event.target.files[0]; const fileReader = new FileReader(); fileReader.addEventListener('loadend', (evt) => { if (evt.target.readyState == FileReader.DONE) { const hash = CryptoJS.SHA256(fileReader.result); console.log(hash.toString()); } }); fileReader.readAsDataURL(file); }

 <script src="https://cdnjs.cloudflare.com/ajax/libs/crypto-js/4.0.0/crypto-js.min.js"></script> <input type="file" #fileInput onchange="fileChange(event)" />