将自签名证书与 .NET 的 HttpWebRequest/Response 一起使用

Question

我正在尝试连接到使用自签名 SSL 证书的 API。 我使用 .NET 的 HttpWebRequest 和 HttpWebResponse 对象来执行此操作。 我得到一个例外：

底层连接已关闭：无法建立 SSL/TLS 安全通道的信任关系。

我明白这意味着什么。 我理解为什么 .NET 认为它应该警告我并关闭连接。 但在这种情况下，我只想连接到 API，不管中间人攻击如何。

那么，我该如何为这个自签名证书添加例外呢？ 或者是告诉 HttpWebRequest/Response 根本不验证证书的方法？ 我该怎么做呢？

Answer 1

事实证明，如果您只想完全禁用证书验证，则可以更改 ServicePointManager 上的 ServerCertificateValidationCallback，如下所示：

ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

这将验证所有证书（包括无效、过期或自签名的证书）。

Answer 2

@Domster：这可行，但您可能希望通过检查证书哈希是否与您的期望相匹配来强制执行一些安全性。 因此，扩展版本看起来有点像这样（基于我们正在使用的一些实时代码）：

static readonly byte[] apiCertHash = { 0xZZ, 0xYY, ....};

/// <summary>
/// Somewhere in your application's startup/init sequence...
/// </summary>
void InitPhase()
{
    // Override automatic validation of SSL server certificates.
    ServicePointManager.ServerCertificateValidationCallback =
           ValidateServerCertficate;
}

/// <summary>
/// Validates the SSL server certificate.
/// </summary>
/// <param name="sender">An object that contains state information for this
/// validation.</param>
/// <param name="cert">The certificate used to authenticate the remote party.</param>
/// <param name="chain">The chain of certificate authorities associated with the
/// remote certificate.</param>
/// <param name="sslPolicyErrors">One or more errors associated with the remote
/// certificate.</param>
/// <returns>Returns a boolean value that determines whether the specified
/// certificate is accepted for authentication; true to accept or false to
/// reject.</returns>
private static bool ValidateServerCertficate(
        object sender,
        X509Certificate cert,
        X509Chain chain,
        SslPolicyErrors sslPolicyErrors)
{
    if (sslPolicyErrors == SslPolicyErrors.None)
    {
        // Good certificate.
        return true;
    }

    log.DebugFormat("SSL certificate error: {0}", sslPolicyErrors);

    bool certMatch = false; // Assume failure
    byte[] certHash = cert.GetCertHash();
    if (certHash.Length == apiCertHash.Length)
    {
        certMatch = true; // Now assume success.
        for (int idx = 0; idx < certHash.Length; idx++)
        {
            if (certHash[idx] != apiCertHash[idx])
            {
                certMatch = false; // No match
                break;
            }
        }
    }

    // Return true => allow unauthenticated server,
    //        false => disallow unauthenticated server.
    return certMatch;
}

Answer 3

您可以覆盖每个 HttpWebRequest 本身的 SSL 验证（而不是通过影响所有请求的全局委托）：

请注意，在 .NET 4.5 中， net.httpwebrequest.servercertificatevalidationcallback.aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.servercertificatevalidationcallback.aspx

HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(uri);
request.ServerCertificateValidationCallback = delegate { return true; };

Answer 4

将自签名证书添加到本地计算机受信任的根证书颁发机构

您可以通过以管理员身份运行 MMC 来导入证书。

如何：使用 MMC 管理单元查看证书

Answer 5

Domster 的回答中使用的验证回调的范围可以使用 上的 sender 参数限制为特定请求ServerCertificateValidationCallback 委托。 以下简单的作用域类使用此技术临时连接仅针对给定请求对象执行的验证回调。

public class ServerCertificateValidationScope : IDisposable
{
    private readonly RemoteCertificateValidationCallback _callback;

    public ServerCertificateValidationScope(object request,
        RemoteCertificateValidationCallback callback)
    {
        var previous = ServicePointManager.ServerCertificateValidationCallback;
        _callback = (sender, certificate, chain, errors) =>
            {
                if (sender == request)
                {
                    return callback(sender, certificate, chain, errors);
                }
                if (previous != null)
                {
                    return previous(sender, certificate, chain, errors);
                }
                return errors == SslPolicyErrors.None;
            };
        ServicePointManager.ServerCertificateValidationCallback += _callback;
    }

    public void Dispose()
    {
        ServicePointManager.ServerCertificateValidationCallback -= _callback;
    }
}

上面的类可用于忽略特定请求的所有证书错误，如下所示：

var request = WebRequest.Create(uri);
using (new ServerCertificateValidationScope(request, delegate { return true; }))
{
    request.GetResponse();
}

Answer 6

只是以 devstuff 的答案为基础，包括主题和发行者...欢迎评论...

public class SelfSignedCertificateValidator
{
    private class CertificateAttributes
    {
        public string Subject { get; private set; }
        public string Issuer { get; private set; }
        public string Thumbprint { get; private set; }

        public CertificateAttributes(string subject, string issuer, string thumbprint)
        {
            Subject = subject;
            Issuer = issuer;                
            Thumbprint = thumbprint.Trim(
                new char[] { '\u200e', '\u200f' } // strip any lrt and rlt markers from copy/paste
                ); 
        }

        public bool IsMatch(X509Certificate cert)
        {
            bool subjectMatches = Subject.Replace(" ", "").Equals(cert.Subject.Replace(" ", ""), StringComparison.InvariantCulture);
            bool issuerMatches = Issuer.Replace(" ", "").Equals(cert.Issuer.Replace(" ", ""), StringComparison.InvariantCulture);
            bool thumbprintMatches = Thumbprint == String.Join(" ", cert.GetCertHash().Select(h => h.ToString("x2")));
            return subjectMatches && issuerMatches && thumbprintMatches; 
        }
    }

    private readonly List<CertificateAttributes> __knownSelfSignedCertificates = new List<CertificateAttributes> {
        new CertificateAttributes(  // can paste values from "view cert" dialog
            "CN = subject.company.int", 
            "CN = issuer.company.int", 
            "f6 23 16 3d 5a d8 e5 1e 13 58 85 0a 34 9f d6 d3 c8 23 a8 f4") 
    };       

    private static bool __createdSingleton = false;

    public SelfSignedCertificateValidator()
    {
        lock (this)
        {
            if (__createdSingleton)
                throw new Exception("Only a single instance can be instanciated.");

            // Hook in validation of SSL server certificates.  
            ServicePointManager.ServerCertificateValidationCallback += ValidateServerCertficate;

            __createdSingleton = true;
        }
    }

    /// <summary>
    /// Validates the SSL server certificate.
    /// </summary>
    /// <param name="sender">An object that contains state information for this
    /// validation.</param>
    /// <param name="cert">The certificate used to authenticate the remote party.</param>
    /// <param name="chain">The chain of certificate authorities associated with the
    /// remote certificate.</param>
    /// <param name="sslPolicyErrors">One or more errors associated with the remote
    /// certificate.</param>
    /// <returns>Returns a boolean value that determines whether the specified
    /// certificate is accepted for authentication; true to accept or false to
    /// reject.</returns>
    private bool ValidateServerCertficate(
        object sender,
        X509Certificate cert,
        X509Chain chain,
        SslPolicyErrors sslPolicyErrors)
    {
        if (sslPolicyErrors == SslPolicyErrors.None)
            return true;   // Good certificate.

        Dbg.WriteLine("SSL certificate error: {0}", sslPolicyErrors);
        return __knownSelfSignedCertificates.Any(c => c.IsMatch(cert));            
    }
}

Answer 7

添加作为对其他人的可能帮助...如果您希望它提示用户安装自签名证书，您可以使用此代码（从上面修改）。

不需要管理员权限，安装到本地用户信任的配置文件：

    private static bool ValidateServerCertficate(
        object sender,
        X509Certificate cert,
        X509Chain chain,
        SslPolicyErrors sslPolicyErrors)
    {
        if (sslPolicyErrors == SslPolicyErrors.None)
        {
            // Good certificate.
            return true;
        }

        Common.Helpers.Logger.Log.Error(string.Format("SSL certificate error: {0}", sslPolicyErrors));
        try
        {
            using (X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser))
            {
                store.Open(OpenFlags.ReadWrite);
                store.Add(new X509Certificate2(cert));
                store.Close();
            }
            return true;
        }
        catch (Exception ex)
        {
            Common.Helpers.Logger.Log.Error(string.Format("SSL certificate add Error: {0}", ex.Message));
        }

        return false;
    }

这似乎对我们的应用程序很有效，如果用户按否，通信将无法进行。

更新：2015-12-11 - 将 StoreName.Root 更改为 StoreName.My - My 将安装到本地用户存储中，而不是 Root。 即使您“以管理员身份运行”，在某些系统上 root 也无法工作

Answer 8

首先 - 我很抱歉，因为我已经使用了@devstuff 描述的解决方案。 不过，我找到了一些改进的方法。

• 添加自签名证书处理
• 通过证书的原始数据进行比较
• 实际证书颁发机构验证
• 一些附加注释和改进

这是我的修改：

private static X509Certificate2 caCertificate2 = null;

/// <summary>
/// Validates the SSL server certificate.
/// </summary>
/// <param name="sender">An object that contains state information for this validation.</param>
/// <param name="cert">The certificate used to authenticate the remote party.</param>
/// <param name="chain">The chain of certificate authorities associated with the remote certificate.</param>
/// <param name="sslPolicyErrors">One or more errors associated with the remote certificate.</param>
/// <returns>Returns a boolean value that determines whether the specified certificate is accepted for authentication; true to accept or false to reject.</returns>
private static bool ValidateServerCertficate(
        object sender,
        X509Certificate cert,
        X509Chain chain,
        SslPolicyErrors sslPolicyErrors)
{
    if (sslPolicyErrors == SslPolicyErrors.None)
    {
        // Good certificate.
        return true;
    }

    // If the following line is not added, then for the self-signed cert an error will be (not tested with let's encrypt!):
    // "A certificate chain processed, but terminated in a root certificate which is not trusted by the trust provider. (UntrustedRoot)"
    chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllowUnknownCertificateAuthority;

    // convert old-style cert to new-style cert
    var returnedServerCert2 = new X509Certificate2(cert);

    // This part is very important. Adding known root here. It doesn't have to be in the computer store at all. Neither do certificates.
    chain.ChainPolicy.ExtraStore.Add(caCertificate2);

    // 1. Checks if ff the certs are OK (not expired/revoked/etc) 
    // 2. X509VerificationFlags.AllowUnknownCertificateAuthority will make sure that untrusted certs are OK
    // 3. IMPORTANT: here, if the chain contains the wrong CA - the validation will fail, as the chain is wrong!
    bool isChainValid = chain.Build(returnedServerCert2);
    if (!isChainValid)
    {
        string[] errors = chain.ChainStatus
            .Select(x => String.Format("{0} ({1})", x.StatusInformation.Trim(), x.Status))
            .ToArray();

        string certificateErrorsString = "Unknown errors.";

        if (errors != null && errors.Length > 0)
        {
            certificateErrorsString = String.Join(", ", errors);
        }

        Log.Error("Trust chain did not complete to the known authority anchor. Errors: " + certificateErrorsString);
        return false;
    }

    // This piece makes sure it actually matches your known root
    bool isValid = chain.ChainElements
        .Cast<X509ChainElement>()
        .Any(x => x.Certificate.RawData.SequenceEqual(caCertificate2.GetRawCertData()));

    if (!isValid)
    {
        Log.Error("Trust chain did not complete to the known authority anchor. Thumbprints did not match.");
    }

    return isValid;
}

设置证书：

caCertificate2 = new X509Certificate2("auth/ca.crt", "");
var clientCertificate2 = new X509Certificate2("auth/client.pfx", "");

传递委托方法

ServerCertificateValidationCallback(ValidateServerCertficate)

client.pfx 是使用 KEY 和 CERT 生成的，如下所示：

openssl pkcs12 -export -in client.crt -inkey client.key -out client.pfx

Answer 9

要记住的一件事是，拥有 ServicePointManager.ServerCertificateValidationCallback 似乎并不意味着 CRL 检查和服务器名称验证未完成，它仅提供了一种覆盖其结果的方法。 因此，您的服务可能仍需要一段时间才能获得 CRL，之后您才会知道它未通过某些检查。

Answer 10

我遇到了与OP相同的问题，其中网络请求会抛出确切的异常。 我认为所有设置都正确，证书已安装，我可以很好地在机器存储中找到它并将其附加到 Web 请求，并且我已禁用请求上下文中的证书验证。

事实证明，我正在我的用户帐户下运行，并且证书已安装到机器存储中。 这导致 Web 请求抛出此异常。 为了解决这个问题，我必须以管理员身份运行或将证书安装到用户存储并从那里读取它。

看起来 C# 能够在机器存储中找到证书，即使它不能与 Web 请求一起使用，这会导致在发出 Web 请求后引发 OP 的异常。