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Canvas Fingerprint Blocker

Block HTML canvas element from being used for fingerprinting purposes

  1. // ==UserScript==
  2. // @name         Canvas Fingerprint Blocker
  3. // @namespace    https://github.com/joue-quroi/canvas-fingerprint-blocker
  4. // @version      0.1
  5. // @description  Block HTML canvas element from being used for fingerprinting purposes
  6. // @author       Joue Quroi
  7. // @match        *://*/*
  8. // @grant        none
  9. // ==/UserScript==
  10.  
  11. (function() {
  12.     'use strict';
  13.  
  14.     if (document instanceof XMLDocument) {
  15.         return;
  16.     }
  17.  
  18.     // https://add0n.com/canvas-fingerprint-blocker.html
  19.     // https://github.com/joue-quroi/canvas-fingerprint-blocker
  20.     // https://mybrowseraddon.com/canvas-defender.html
  21.     // Modified by Ganlv
  22.  
  23.     const toBlob = HTMLCanvasElement.prototype.toBlob;
  24.     const toDataURL = HTMLCanvasElement.prototype.toDataURL;
  25.  
  26.     HTMLCanvasElement.prototype.htGfd = function() {
  27.         const {width, height} = this;
  28.         const context = this.getContext('2d');
  29.         const shift = {
  30.             'r': Math.floor(Math.random() * 10) - 5,
  31.             'g': Math.floor(Math.random() * 10) - 5,
  32.             'b': Math.floor(Math.random() * 10) - 5
  33.         };
  34.         const matt = context.getImageData(0, 0, width, height);
  35.         for (let i = 0; i < height; i += 3) {
  36.             for (let j = 0; j < width; j += 3) {
  37.                 const n = ((i * (width * 4)) + (j * 4));
  38.                 matt.data[n + 0] = matt.data[n + 0] + shift.r;
  39.                 matt.data[n + 1] = matt.data[n + 1] + shift.g;
  40.                 matt.data[n + 2] = matt.data[n + 2] + shift.b;
  41.             }
  42.         }
  43.         context.putImageData(matt, 0, 0);
  44.         this.htGfd = () => {
  45.             window.top.postMessage('htGfd-called', '*');
  46.         };
  47.         window.top.postMessage('htGfd-called', '*');
  48.     };
  49.  
  50.     Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
  51.         value: function() {
  52.             if (document.documentElement.dataset.htgfd !== 'false') {
  53.                 this.htGfd();
  54.             }
  55.             return toBlob.apply(this, arguments);
  56.         }
  57.     });
  58.     Object.defineProperty(HTMLCanvasElement.prototype, 'toDataURL', {
  59.         value: function() {
  60.             if (document.documentElement.dataset.htgfd !== 'false') {
  61.                 this.htGfd();
  62.             }
  63.             return toDataURL.apply(this, arguments);
  64.         }
  65.     });
  66.     document.documentElement.dataset.htGfd = true;
  67. })();