From 447ff542223350db2328ee28b608f0c30db1377c Mon Sep 17 00:00:00 2001
From: kkapsner <github@mail.kkapsner.de>
Date: Wed, 18 May 2016 08:55:21 +0200
Subject: [PATCH] Made random changes constant within the same domain.

---
 lib/modifiedAPI.js | 47 +++++++++++++++-------------------------------
 1 file changed, 15 insertions(+), 32 deletions(-)

diff --git a/lib/modifiedAPI.js b/lib/modifiedAPI.js
index d130147..e4a3855 100644
--- a/lib/modifiedAPI.js
+++ b/lib/modifiedAPI.js
@@ -5,7 +5,16 @@
 (function(){
 	"use strict";
 	
+	const rnd = {};
 	function getFakeCanvas(window, original){
+		var domain = window.document.location.host;
+		if (!rnd[domain]){
+			rnd[domain] = new Uint8Array(128);
+			for (var i = 0; i < rnd[domain].length; i += 1){
+				rnd[domain][i] = Math.floor(Math.random() * 0xFF);
+			}
+			console.log("created new rnd for domain", domain);
+		}
 		var context = window.HTMLCanvasElement.prototype.getContext.call(original, "2d");
 		var imageData, data, source;
 		if (context){
@@ -29,40 +38,14 @@
 		}
 		data = imageData.data;
 		var l = data.length;
-		var randomI = 65536;
-		var randomOffset = 0;
-		var randomNumbers = new Uint8Array(Math.min(65536, l));
 		
-		for (var i = 0; i < l; i += 1, randomI += 1){
-			if (randomI >= randomNumbers.length){
-				randomI = 0;
-				randomOffset += randomNumbers.length;
-				if (l - i < 65536){
-					randomNumbers = new Uint8Array(l - i);
-				}
-				window.crypto.getRandomValues(randomNumbers);
-			}
-			var rnd = randomNumbers[randomI];
+		for (var i = 0; i < l; i += 1){
 			var value = source[i];
-			if (value >= 0x80){
-				value = value ^ (rnd & 0x1F);
-			}
-			else if (value >= 0x40){
-				value = value ^ (rnd & 0x0F);
-			}
-			else if (value >= 0x20){
-				value = value ^ (rnd & 0x07);
-			}
-			else if (value >= 0x10){
-				value = value ^ (rnd & 0x03);
-			}
-			else if (value >= 0x08){
-				value = value ^ (rnd & 0x01);
-			}
-			// else if (value >= 0x04){
-				// value = value ^ (rnd * 0x00);
-			// }
-			data[i] = value;
+			var index = value & 0x7F;
+			var bitIndex = ((i & 0x03) << 1) | (value >>> 7);
+			var bit = (rnd[domain][index] >>> bitIndex) & 0x01;
+			if (bitIndex % 2) console.log(rnd[domain][index], index, bitIndex, bit);
+			data[i] = value ^ bit;
 		}
 		var canvas = original.cloneNode(true);
 		context = window.HTMLCanvasElement.prototype.getContext.call(canvas, "2d");