SSL编程---客户端回调函数

如果需要访问一个带有 ssl 的网站或 Web Service 时，需要添加一个回调函数。

using System.Net;

using System.Net.Security;

using System.Security.Cryptography;

using System.Security.Cryptogryaphy.X509Certificates;

WebServiceClient client = new WebServiceClient(); //WebServiceClient 可以通过添加 Web 服务引用的方式获取，如何添加不再熬述

ServicePointManager.ServiceCertificateValidationCallback += ValidateRemoteCertificateWhenCallback;

 private static bool ValidateRemoteCertificateWhenCallback(object sender, X509Certificate cert, X509Chain chain, SslPolicyErrors errors)
        {
            bool result = false;
            try
            {
                if (sender is WebRequest && cert is X509Certificate2 && chain != null)
                {
                    result = errors == SslPolicyErrors.None; // 表明验证是通过的
                    if (!result)
                    {
                        result = chain.ChainStatus == null; // 证书生成引擎的所有元素的状态为空，证明不需要验证（这种情况实际很少出现）
                        if (!result)
                        {
                            result = chain.ChainStatus.Length <= 0; // 证书生成引擎的数量为 0，不需要验证（这种情况实际很少出现）
                            if (!result)
                            {
                                if (chain.ChainStatus.Length == 1 && chain.ChainStatus[0].Status == X509ChainStatusFlags.NoError)
                                    result = true; // 证明 X509 链是正确的（这种情况很少出现）
                                else // 这是大多数的情况
                                {
                                    result = ((X509Certificate2)cert).Verify(); // 使用基本验证策略执行 X509 链验证（如果客户端与服务端在同一台设备上时会可能出现这种情况）
                                    if (!result)

// 这是大多数的情况，客户端与服务器不在同一台设备上，此时通过远程到服务端去验证证书的合法性，如果验证通过，即证明该证书是合法的
                                    {
                                        if (chain.ChainPolicy == null)
                                            chain.ChainPolicy = new X509ChainPolicy();
                                        chain.ChainPolicy.RevocationFlag = X509RevocationFlag.EntireChain;
                                        chain.ChainPolicy.RevocationMode = X509RevocationMode.Online;
                                        chain.ChainPolicy.UrlRetrievalTimeout = new TimeSpan(0, 0, 30);
                                        chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllFlags;
                                        chain.ChainPolicy.VerificationTime = ((X509Certificate2)cert).NotAfter;
                                        result = chain.Build((X509Certificate2)cert); // 根据指定的策略生成 X509 链，如果能够生成，证明证书是有效的
                                    }
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception e)
            {
                throw e;
            }
            return result;
        }