014.修改chromium源码-修改webGL指纹(二)

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修改chromium源码-修改webGL指纹(二)

一、webGL指纹是什么

之前介绍过webGL指纹和常见网站绕过webGL指纹，插眼传送

二、为啥有的webGL指纹-二期

上期我们通过修改gl的参数，getSupportedExtensions()函数返回值列表的顺序，绕过部分网站的指纹检测。
但还有些网站通过webGL生成图形来获取指纹，我们就需要再出一期了。
还有就是：上期指纹检测未通过browserscan这个网站。

三、获取浏览器的webGL指纹(通过生成图像)

有攻才有防，先看看网站是如何通过js获取你的webGL指纹的。
将下面的代码复制到F12控制台，就可以获取显示你的webGL指纹了。


async function sha256(message) {// 把字符串转换为Uint8Arrayconst msgBuffer = new TextEncoder().encode(message);// 计算散列值const hashBuffer = await crypto.subtle.digest('SHA-256', msgBuffer);// 转换为数组const hashArray = Array.from(new Uint8Array(hashBuffer));// 转换为16进制字符串const hashHex = hashArray.map(b => b.toString(16).padStart(2, '0')).join('');return hashHex;
}function getWebGLFingerprint() {var canvas = document.createElement('canvas');var gl = canvas.getContext("webgl") || canvas.getContext("experimental-webgl");// 设置清除颜色为黑色，不透明gl.clearColor(0.0, 0.0, 0.0, 1.0);// 清除颜色缓冲区gl.clear(gl.COLOR_BUFFER_BIT);// 创建顶点着色器var vsSource = `attribute vec4 aVertexPosition;void main(void) {gl_Position = aVertexPosition;}`;var vertexShader = gl.createShader(gl.VERTEX_SHADER);gl.shaderSource(vertexShader, vsSource);gl.compileShader(vertexShader);// 创建片段着色器var fsSource = `void main(void) {gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);}`;var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);gl.shaderSource(fragmentShader, fsSource);gl.compileShader(fragmentShader);// 创建着色器程序var shaderProgram = gl.createProgram();gl.attachShader(shaderProgram, vertexShader);gl.attachShader(shaderProgram, fragmentShader);gl.linkProgram(shaderProgram);gl.useProgram(shaderProgram);// 定义三角形的顶点var vertices = new Float32Array([0.0,  1.0,  0.0,-1.0, -1.0,  0.0,1.0, -1.0,  0.0]);// 创建顶点缓冲区对象var vertexBuffer = gl.createBuffer();gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);// 将缓冲区对象绑定到着色器变量var vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");gl.enableVertexAttribArray(vertexPositionAttribute);gl.vertexAttribPointer(vertexPositionAttribute, 3, gl.FLOAT, false, 0, 0);// 绘制三角形gl.drawArrays(gl.TRIANGLES, 0, 3);// 读取渲染结果并生成指纹//var pixels = new Uint8Array(gl.drawingBufferWidth * gl.drawingBufferHeight * 4);//gl.readPixels(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight, gl.RGBA, gl.UNSIGNED_BYTE, pixels);//return pixels;var res = canvas.toDataURL()return res
}sha256(getWebGLFingerprint()).then(hash => console.log(hash));

可以看到：获取图像数据有2种方式，关键函数是readPixels()和toDataURL()。

四、修改源码的readPixels()函数

打开源码文件 \third_party\blink\renderer\modules\webgl\webgl_rendering_context_base.cc

1.找到下面的代码

void WebGLRenderingContextBase::ReadPixelsHelper(GLint x,GLint y,GLsizei width,GLsizei height,GLenum format,GLenum type,DOMArrayBufferView* pixels,int64_t offset) {if (isContextLost())return;

2.替换为

int getRandomIntForFoo12Modern() {static std::mt19937 generator(static_cast<unsigned long>(time(NULL))); // 静态以确保只初始化一次std::uniform_int_distribution<int> distribution(0, 9);return distribution(generator);
}void WebGLRenderingContextBase::ReadPixelsHelper(GLint x,GLint y,GLsizei width,GLsizei height,GLenum format,GLenum type,DOMArrayBufferView* pixels,int64_t offset) {if (isContextLost())return;//追加2行width = width - getRandomIntForFoo12Modern();height = height - getRandomIntForFoo12Modern();

注意：这里我们通过裁剪了部分像素来实现改变ReadPixelsHelper方法的返回值

五、修改源码的toDataURL()函数

打开源码文件 \third_party\blink\renderer\core\html\canvas\html_canvas_element.cc

1.头部加上(随便加在一个`#include`后面)

#include <algorithm> 
#include <random>    
#include <chrono>

2.找到下面的代码


String HTMLCanvasElement::toDataURL(const String& mime_type,const ScriptValue& quality_argument,ExceptionState& exception_state) const {if (ContextHasOpenLayers(context_)) {exception_state.ThrowDOMException(DOMExceptionCode::kInvalidStateError,"`toDataURL()` cannot be called with open layers.");return String();}if (!OriginClean()) {exception_state.ThrowSecurityError("Tainted canvases may not be exported.");return String();}double quality = kUndefinedQualityValue;if (!quality_argument.IsEmpty()) {v8::Local<v8::Value> v8_value = quality_argument.V8Value();if (v8_value->IsNumber())quality = v8_value.As<v8::Number>()->Value();}String data = ToDataURLInternal(mime_type, quality, kBackBuffer);TRACE_EVENT_INSTANT(TRACE_DISABLED_BY_DEFAULT("identifiability.high_entropy_api"),"CanvasReadback", "data_url", data.Utf8());return data;
}

注意：最新源码可能和当前代码有略微差异，但基本逻辑是一样。要做的是给返回值后面加空格

3.替换为

String HTMLCanvasElement::toDataURL(const String& mime_type,const ScriptValue& quality_argument,ExceptionState& exception_state) const {if (ContextHasOpenLayers(context_)) {exception_state.ThrowDOMException(DOMExceptionCode::kInvalidStateError,"`toDataURL()` cannot be called with open layers.");return String();}if (!OriginClean()) {exception_state.ThrowSecurityError("Tainted canvases may not be exported.");return String();}double quality = kUndefinedQualityValue;if (!quality_argument.IsEmpty()) {v8::Local<v8::Value> v8_value = quality_argument.V8Value();if (v8_value->IsNumber())quality = v8_value.As<v8::Number>()->Value();}String data = ToDataURLInternal(mime_type, quality, kBackBuffer);TRACE_EVENT_INSTANT(TRACE_DISABLED_BY_DEFAULT("identifiability.high_entropy_api"),"CanvasReadback", "data_url", data.Utf8());//这里追加几行std::srand(std::time(nullptr));int randomNum = std::rand() % 100 + 1;std::string spaces(randomNum, ' ');data = data + String(spaces);//LOG(ERROR) << "data:('" << data << "') data";return data;
}