前言

本文主要是自定义实现滑块验证码，下面是一些滑块验证码的一些概念。

1.滑块验证码的定义

滑块验证码是一种很常见的行为验证码，用户只需要轻轻滑动滑块填充拼图，即可完成安全验证。通常包括触发式、嵌入式和弹出式三种形式。

2.滑块验证码的安全性分析

滑块验证码对机器验证的判断，不只是完成前端的拼图，还有是在后端。不是说你滑动到正确位置就是验证通过，而是根据特征识别来区分是否为真用户，滑到正确位置只是一个必要条件。比如通过记录真人用户的滑动平均速度，用户鼠标点击情况，以及滑动后的匹配程度来识别是否是真实用户行为等。

验证码后台还会针对用户产生的行为轨迹数据进行机器学习建模，结合访问频率、地理位置、历史记录等多个维度信息，快速、准确地返回人机判定结果，故而机器的识别+模拟行为是不容易通过的。

当然滑块验证码也不是万无一失，但对滑动行为的模拟需要比较强的破解能力，毕竟还是大幅提升了攻击成本，而且技术也会在攻防转换中不断进步。

3.滑块验证码的第三方服务

如果有安全验证需求，建议可以接入第三方服务，比如网易易盾行为验证码，提供智能无感知、滑动拼图、文字点选、图标点选、推理拼图验证、短信上行等验证方式。

一、滑动验证码和拼图验证功能实现

1.逻辑分析

滑动验证码的逻辑：

1. 服务器生成主图+附图（从主图裁剪下来的不需要管y坐标）并且存储X坐标
2. 前端传入本地X坐标到服务器
3. 服务器进行计算存储X坐标和本地X坐标相差值
4. 验证相差值是否在 0-2 之间，判断 true | false

2.新建项目

按下面步骤创建.NET 7项目

3.配置缓存

在Program.cs文件在配置

builder.Services.AddDistributedMemoryCache();
builder.Services.AddSession(options =>
{
    options.Cookie.Name = ".AdventureWorks.Session"; 
    options.IdleTimeout = TimeSpan.FromSeconds(2000);//设置session的过期时间 
    options.Cookie.HttpOnly = true;//设置在浏览器不能通过js获得该cookie的值 
});

app.UseSession();//添加会话中间件
app.UseRouting();//路由中间件

4.配置跨域

安装nuget包：Microsoft.AspNetCore.Cors

#region 添加跨域
builder.Services.AddCors(options =>
{
options.AddPolicy("any",
    builder => builder.AllowAnyOrigin()
    .WithMethods("GET", "POST", "HEAD", "PUT", "DELETE", "OPTIONS").AllowAnyHeader()
);
});
#endregion

app.UseCors("any");//使用跨域

控制器使用

[EnableCors("any")]

5.后端源码

Captcha.cs

public class Captcha
    {

        public static Captcha64Model GenerateBase64()
        {
            CaptchaModel model = Captcha.Generate();
            if (model != null)
            {
                return new Captcha64Model()
                {
                    X = model.X,
                    Y = model.Y,
                    Background = ImageToBase64(model.Background, ImageFormat.Jpeg),
                    Slide = ImageToBase64(model.Slide, ImageFormat.Png)
                };
            }
            else
            {
                return null;
            }
        }

        /// <summary>
        /// 生成验证码
        /// </summary>
        /// <returns></returns>
        public static CaptchaModel Generate()
        {
            Bitmap image = BgImage();
            if (image != null)
            {
                int l = Config.l;
                int d = Config.d;
                int width = image.Width;
                int height = image.Height;
                int x = RandomNext(width / 3, width - d - l - 10);//初始x
                int y = RandomNext(10 + d, height - l - 10); ;//初始y
                GraphicsPath path = GetSliderPath(x, y);
                Graphics g = GetGraphics(image);

                //水印
                if (Config.showWatermark)
                {
                    Font font = new Font("宋体", 12, FontStyle.Bold);
                    SizeF size = g.MeasureString(Config.watermarkText, font);
                    Point Plogo = new Point((int)(width - size.Width - 5), (int)(height - size.Height - 5));
                    Color color = image.GetPixel(Plogo.X, Plogo.Y);
                    SolidBrush bru = new SolidBrush(AntiColor(color));
                    g.DrawString(Config.watermarkText, font, bru, Plogo);
                }

                Pen pen = new Pen(Color.FromArgb(200, 255, 255, 255), 2);
                g.DrawPath(pen, path);
                Image slider = CaptureSlider(image, path, x, width, height);
                SolidBrush brush = new SolidBrush(Color.FromArgb(100, 255, 255, 255));
                g.FillPath(brush, path);
                g.Save();
                g.Dispose();
                return new CaptchaModel()
                {
                    X = x,
                    Y = y,
                    Background = image,
                    Slide = slider
                };
            }
            return null;
        }




        /// <summary>
        /// 获取图片Graphics
        /// </summary>
        /// <param name="image"></param>
        /// <returns></returns>
        private static Graphics GetGraphics(Image image)
        {
            Graphics g = Graphics.FromImage(image);
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.InterpolationMode = InterpolationMode.High;
            return g;
        }

        /// <summary>
        /// 获取滑块path
        /// </summary>
        private static GraphicsPath GetSliderPath(int x, int y)
        {
            int l = Config.l;
            int r = Config.r;
            int b = Config.b;
            int c = Config.c;
            int d = Config.d;
            int blod = Config.blod;
            GraphicsPath path = new GraphicsPath(FillMode.Winding);
            Point Pa = new Point(x, y);
            Point Pb = new Point(x + l / 2 - b, y - c + blod);
            Point Pd = new Point(x + l, y);
            Point Pe = new Point(Pd.X + c - blod, y + l / 2 - b);
            Point Pg = new Point(Pd.X, y + l);
            Point Ph = new Point(x, y + l);
            Point Pj = new Point(x + c - blod, Pe.Y);
            path.AddLine(Pa, Pb);
            path.AddArc(x + l / 2 - r, y - d, d, d, 130f, 280f);
            path.AddLines(new Point[] { Pd, Pe });
            path.AddArc(x + l, y + l / 2 - r, d, d, 220f, 280f);
            path.AddLines(new Point[] { Pg, Ph });
            path.AddArc(x, y + l / 2 - r, d, d, 140f, -280f);
            path.AddLine(Pj, Pa);
            return path;
        }


        /// <summary>
        /// 获取滑块区域
        /// </summary>
        /// <param name="image"></param>
        /// <param name="path"></param>
        /// <param name="x"></param>
        /// <param name="width"></param>
        /// <param name="height"></param>
        /// <returns></returns>
        private static Image CaptureSlider(Image image, GraphicsPath path, int x, int width, int height)
        {
            Bitmap concave = new Bitmap(image.Width, image.Height);
            Graphics g = GetGraphics(concave);
            TextureBrush brush = new TextureBrush(image);
            g.Clear(Color.Transparent);
            g.FillPath(brush, path);
            g.Dispose();
            return CaptureImage(concave, x, height);
        }


        /// <summary>
        /// 裁剪图片
        /// </summary>
        /// <param name="fromImage"></param>
        /// <param name="offsetX"></param>
        /// <param name="width"></param>
        /// <param name="height"></param>
        /// <returns></returns>
        private static Image CaptureImage(Image fromImage, int offsetX, int height)
        {
            int width = Config.l + Config.d + Config.blod;
            Bitmap bitmap = new Bitmap(width, height);
            Graphics g = GetGraphics(bitmap);
            g.DrawImage(fromImage, 0, 0, new Rectangle(offsetX, 0, width, height), GraphicsUnit.Pixel);
            g.Dispose();
            return bitmap;
        }


        /// <summary>
        /// 生成随机数
        /// </summary>
        /// <param name="min"></param>
        /// <param name="max"></param>
        /// <returns></returns>
        private static int RandomNext(int min, int max)
        {
            Random random = new Random(Guid.NewGuid().GetHashCode());
            return random.Next(min, max);
        }


        /// <summary>
        /// 取反色
        /// </summary>
        /// <param name="color"></param>
        /// <returns></returns>
        public static Color AntiColor(Color color)
        {
            if (color.R > 128 && color.G > 128 && color.B > 128)
            {
                return Color.Black;
            }
            else
            {
                return Color.White;
            }

        }

        /// <summary>
        /// 获取背景图
        /// </summary>
        /// <returns></returns>
        private static Bitmap BgImage()
        {
            WebClient web = new WebClient();
            int num = RandomNext(1, 20);
            Stream stream = web.OpenRead($"http://00x1.com/images/Pic/{num}.jpg");
            Bitmap bitmap = (Bitmap)Image.FromStream(stream);
            return bitmap;
        }



        /// <summary>
        /// base64转图片
        /// </summary>
        /// <param name="base64string"></param>
        /// <returns></returns>
        public static Bitmap Base64ToImage(string base64string)
        {
            byte[] b = Convert.FromBase64String(base64string);
            MemoryStream ms = new MemoryStream(b);
            Bitmap bitmap = new Bitmap(ms);
            return bitmap;
        }

        /// <summary>
        /// 图片转base64
        /// </summary>
        /// <param name="image"></param>
        /// <returns></returns>
        public static string ImageToBase64(Image image, ImageFormat format)
        {
            if (image == null) return string.Empty;
            string strbaser64 = "";
            try
            {
                string head = "";
                string formatName = ImgFormat.NameFromGuid(format);
                head = $"data:image/{formatName.ToLower()};base64,";
                MemoryStream ms = new MemoryStream();
                image.Save(ms, format);
                byte[] arr = new byte[ms.Length];
                ms.Position = 0;
                ms.Read(arr, 0, (int)ms.Length);
                ms.Close();
                strbaser64 = head + Convert.ToBase64String(arr);
            }
            catch (Exception)
            {
                throw new Exception("Something wrong during convert!");
            }
            return strbaser64;
        }

    }

CaptchaModel.cs

public class CaptchaModel
    {
        public int X { get; set; }
        public int Y { get; set; }
        public Image Background { get; set; }
        public Image Slide { get; set; }
    }
    public class Captcha64Model
    {
        public int X { get; set; }
        public int Y { get; set; }
        public string Background { get; set; }
        public string Slide { get; set; }
    }

Config.cs

public class Config
    {
        /// <summary>
        /// 矩形宽
        /// </summary>
        public static int l = 42;
        /// <summary>
        /// 圆形半径
        /// </summary>
        public static int r = 9;
        /// <summary>
        /// 圆形直径
        /// </summary>
        public static int d = r * 2;
        /// <summary>
        /// 计算圆形与矩形交接三角形边
        /// </summary>
        public static int a = (int)(r * Math.Sin(Math.PI * (50 / 180f)));
        public static int b = (int)(r * Math.Cos(Math.PI * (50 / 180f)));
        public static int c = r - a;
        /// <summary>
        /// 滑块边框
        /// </summary>
        public static int blod = 2;
        /// <summary>
        /// 水印
        /// </summary>
        public static string watermarkText = "YG.NET";
        /// <summary>
        /// 是否显示水印
        /// </summary>
        public static bool showWatermark = true;

    }

ImgFormat.cs

public class ImgFormat
    {

        private static Dictionary<string, string> Formats = new Dictionary<string, string>() {
                            {"b96b3caa-0728-11d3-9d7b-0000f81ef32e","MemoryBmp"},
                            {"b96b3cab-0728-11d3-9d7b-0000f81ef32e","Bmp"},
                            {"b96b3cac-0728-11d3-9d7b-0000f81ef32e","Emf"},
                            {"b96b3cad-0728-11d3-9d7b-0000f81ef32e","Wmf"},
                            {"b96b3cae-0728-11d3-9d7b-0000f81ef32e","Jpeg"},
                            {"b96b3caf-0728-11d3-9d7b-0000f81ef32e","Png"},
                            {"b96b3cb0-0728-11d3-9d7b-0000f81ef32e","Gif"},
                            {"b96b3cb1-0728-11d3-9d7b-0000f81ef32e","Tiff"},
                            {"b96b3cb2-0728-11d3-9d7b-0000f81ef32e","Exif"},
                            {"b96b3cb5-0728-11d3-9d7b-0000f81ef32e","Icon"}
        };

        public static ImageFormat FormatFromGuid(ImageFormat format)
        {
            return FormatFromGuid(format.Guid);
        }
        public static ImageFormat FormatFromGuid(Guid guid)
        {
            return FormatFromGuid(guid.ToString());
        }
        public static ImageFormat FormatFromGuid(string guid)
        {
            if (Formats.ContainsKey(guid))
            {
                string name = Formats[guid];
                ImageFormat format = null;
                switch (name)
                {
                    case "MemoryBmp":
                        format = ImageFormat.MemoryBmp;
                        break;
                    case "Bmp":
                        format = ImageFormat.Bmp;
                        break;
                    case "Emf":
                        format = ImageFormat.Emf;
                        break;
                    case "Wmf":
                        format = ImageFormat.Wmf;
                        break;
                    case "Gif":
                        format = ImageFormat.Gif;
                        break;
                    case "Jpeg":
                        format = ImageFormat.Jpeg;
                        break;
                    case "Png":
                        format = ImageFormat.Png;
                        break;
                    case "Tiff":
                        format = ImageFormat.Tiff;
                        break;
                    case "Exif":
                        format = ImageFormat.Exif;
                        break;
                    case "Icon":
                        format = ImageFormat.Icon;
                        break;
                }
                return format;
            }
            else
            {
                return null;
            }

        }



        public static string NameFromGuid(ImageFormat format)
        {
            return NameFromGuid(format.Guid);
        }
        public static string NameFromGuid(Guid guid)
        {
            return NameFromGuid(guid.ToString());
        }
        public static string NameFromGuid(string guid)
        {
            if (Formats.ContainsKey(guid))
            {
                return Formats[guid];
            }
            else
            {
                return string.Empty;
            }

        }

    }

控制器CaptchaController

[ApiController]
    [Route("[controller]/[action]")]
    public class CaptchaController : ControllerBase
    {
        [EnableCors("any")]
        [HttpGet]
        public string GetCaptcha()
        {
            Captcha64Model model = Captcha.GenerateBase64();
            HttpContext.Session.SetInt32("sliderX", model.X);
            Hashtable ht = new Hashtable();
            ht.Add("background", model.Background);
            ht.Add("slider", model.Slide);
            ht.Add("sliderXXXXX", model.X);
            return JsonConvert.SerializeObject(ht);
        }

        /// <summary>
        /// 检查验证
        /// </summary>
        /// <param name="x"></param>
        /// <returns></returns>
        [EnableCors("any")]
        [HttpGet]
        public string CheckCaptcha(int x = 0)
        {
            Hashtable hs = new Hashtable();
            string Mess = "";
            int Code = 0;
            var session = HttpContext.Session.GetInt32("sliderX");//将用户名放入session中 context.Session.Cache.GetCache("sliderX");
            if (session == null)
            {
                Mess = "请刷新验证码";
                Code = 500;
                goto block;
            }
            string sliderXStr = session?.ToString()!;// as string
            int sliderX = Convert.ToInt32(sliderXStr);
            int difX = sliderX - x;
            if (difX >= 0 - Config.blod && difX <= Config.blod)
            {
                Mess = "success";
                Code = 0;
            }
            else
            {
                session = null;
                Mess = "错误";
                Code = 500;
            }
        block:
            hs.Add("Mess", Mess);
            hs.Add("Code", Code);
            return JsonConvert.SerializeObject(hs);
        }
    }

6.启动程序

7.前端访问

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>滑块验证</title>
        <style>
            * {
                -webkit-user-select: none;
                -moz-user-select: none;
                -ms-user-select: none;
                user-select: none;
            }

            .sc-captcha {
                width: 300px;
                margin: 100px auto;
            }

            .sc_net_panel {
                padding: 10px;
            }

            .sc_net_panel>div {
                position: relative;
            }

            .bg_slider {
                position: absolute;
                left: 0;
                top: 0;
            }

            .bg_refresh {
                position: absolute;
                right: 5px;
                top: 5px;
                background: #808080;
                color: #fff;
                border-radius: 3px;
                width: 16px;
                line-height: 16px;
                text-align: center;
                cursor: pointer;
            }

            .sc_net_slider_icon {
                position: absolute;
                left: 0;
                top: 0;
                height: 37px;
                text-align: center;
                border-radius: 5px;
                border: #808080 1px solid;
                width: 37px;
                line-height: 37px;
                cursor: pointer;
            }

            .sc_net_slider_icon:hover {
                color: #fff;
                background: #1991fa;
            }

            .sc_net_slider_text {
                position: absolute;
                left: 0;
                top: 0;
                text-align: center;
                width: 280px;
                color: #45494c;
                border: #808080 1px solid;
                border-radius: 5px;
                line-height: 35px;
                height: 37px;
                cursor: default;
            }

            .sc_net_slider_area {
                position: absolute;
                left: 0;
                top: 0;
                height: 37px;
            }
        </style>
    </head>
    <body>
        <div>
            <div class="sc-captcha">
                <div class="sc_net_panel">
                    <div class="sc_net_bg">
                        <div class="sc_net_bgimg">
                        </div>
                        <div class="bg_refresh" onclick="loadCaptcha()" title="刷新">↻</div>
                    </div>
                </div>
                <div class="sc_net_panel1">
                    <div class="sc_net_panel  ">
                        <div class="sc_net_slider">
                            <div class="sc_net_slider_text">向右拖动滑块填充拼图</div>
                            <div class="sc_net_slider_area"></div>
                            <div id="table1" class="sc_net_slider_icon">➞</div>
                        </div>
                    </div>
                </div>

            </div>
        </div>
        <script src="http://apps.bdimg.com/libs/jquery/2.1.1/jquery.min.js"></script>
        <script>
            var initial_x; //初始坐标
            var end_x; //结束坐标
            var slider = getByClassName0("sc_net_slider_icon"); //获取滑块
            var bg_slider;
            slider.addEventListener('mousedown', handleDragStart);
            slider.addEventListener('touchstart', handleDragStart);
            document.addEventListener('mousemove', handleDragMove);
            document.addEventListener('touchmove', handleDragMove);
            document.addEventListener('mouseup', handleDragEnd);
            document.addEventListener('touchend', handleDragEnd);
            document.addEventListener('mousedown', function () {
                return false;
            });
            document.addEventListener('touchstart', function () {
                return false;
            });
            loadCaptcha();
            //获取图片数据
            function loadCaptcha() {
                $.ajax({
                    url: "https://localhost:7018/Captcha/GetCaptcha",
                    type: "get",
                    dataType: "JSON",
                    crossDomain: true,
                    success: function (json) {
                        $("#table1").css("position", "absolute");//滑块恢复初始位置
                        $("#table1").css("left", 0);//滑块恢复初始位置
                        isMouseDown = false;//滑块禁止移动
                        var bg = createCanvas(280, 155); //定义画布大小
                        bg.className = 'bg_img'; //定义画布名称
                        bg_slider = createCanvas(62, 155); //定义滑块大小
                        bg_slider.className = 'bg_slider'; //定义滑块名称
                        CanvasSetImage(bg, json.background); //创建画布
                        CanvasSetImage(bg_slider, json.slider); //创建滑块
                        /*向界面添加节点*/
                        var doc = document.getElementsByClassName("sc_net_bgimg")[0];
                        doc.innerHTML = "";
                        doc.appendChild(bg);
                        doc.appendChild(bg_slider);
                        /*end*/
                    }
                })
            }
            //设置画布，滑块的大小
            function createCanvas(width, height) {
                var canvas = document.createElement('canvas');
                canvas.width = width;
                canvas.height = height;
                return canvas;
            };
            //创建画布，滑块
            function CanvasSetImage(_canvas, base64) {

                //获取2d画布对象
                var ctx = _canvas.getContext("2d");
                //创建图片标签
                var _img = document.createElement("img");
                //设置图片地址
                _img.src = base64;
                _img.onload = function () {
                    ctx.drawImage(_img, 0, 0);
                }
            }
            //根据类名获取元素
            function getByClassName0(className) {
                return document.getElementsByClassName(className)[0];
            };
            //originX  originY初始坐标
            //clientX  clientY相对于界面的坐标
            //screenX screenY相对于屏幕的坐标
            //isMouseDown=true/false 滑块是否能移动
            var originX, originY, trail = [],
                isMouseDown = false;
            var isOk = false;
            //滑块启动
            function handleDragStart(e) {
                if (isOk) return;
                originX = e.screenX || e.touches[0].clientX;
                originY = e.screenY || e.touches[0].clientY;
                isMouseDown = true;
                initial_x = $(".bg_slider").offset().left; //获取初始坐标

            };
            //滑块拖动
            function handleDragMove(e) {

                if (!isMouseDown) return false;
                var eventX = e.clientX || e.touches[0].clientX;
                var eventY = e.clientY || e.touches[0].clientY;
                var moveX = eventX - originX;
                var moveY = eventY - originY;
                if (moveX >= 0 && moveX <= 243) {
                    slider.style.left = moveX + "px";
                    bg_slider.style.left = moveX / 243 * 218 + "px";
                }
            };
            //滑块结束
            function handleDragEnd(e) {
                if (!isMouseDown) return false;
                isMouseDown = false;
                var eventX = e.clientX || e.changedTouches[0].clientX;
                if (eventX == originX) return false;
                end_x = $(".bg_slider").offset().left; //获取最终坐标
                var result = Math.round(end_x - initial_x);
                $.get("https://localhost:7018/Captcha/CheckCaptcha?x=" + result, function (res) {
                    if (res.Mess == "错误") {
                        alert("出错了，再试一遍吧！");
                        handleDragStart(e);
                        loadCaptcha();
                    } else {
                        alert("恭喜你，已打败80%的用户！");
                    }
                });
            };
        </script>
    </body>
</html>