访问XamarinForms中的自签名X509证书，以便与Mosquitto代理进行mqtt TLS连接

Question

我希望通过自签名x509证书来保护TLS，使用M2MqttDotnetCore客户端连接到mosquitto mqtt代理的许多现有XamarinForms应用程序。

为此，我创建了一个简单的示例XamarinForms发布/订阅聊天应用程序，以了解如何保护XamarinForms mqtt客户端应用程序，该应用程序可以在此GitHub存储库中发声。 jhalbrecht/XamarinFormsMqttSample

我在Mosquitto_pub，python和.net控制台应用程序中有样本，通过TLS和自签名证书，通过端口8883成功连接到mosquitto代理。 XamarinForms UWP应用程序也可以不安全和安全地工作。我在使用Android应用程序在端口8883上使用TLS时遇到问题，Android应用程序在端口1883上运行时不安全。这是Visual Studio 2017的运行时日志

[0:] M2Mqtt.Exceptions.MqttConnectionException: Exception connecting to the broker ---> System.AggregateException: One or more errors occurred. ---> System.Security.Authentication.AuthenticationException: A call to SSPI failed, see inner exception. ---> Mono.Btls.MonoBtlsException: Ssl error:1000007d:SSL routines:OPENSSL_internal:CERTIFICATE_VERIFY_FAILED
  at /Users/builder/jenkins/workspace/xamarin-android-d15-9/xamarin-android/external/mono/external/boringssl/ssl/handshake_client.c:1132
  at Mono.Btls.MonoBtlsContext.ProcessHandshake () [0x00038] in <fb6d78e506844b3b96d5b35aa047fbbd>:0 
  at Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake (Mono.Net.Security.AsyncOperationStatus status) [0x0003e] in <fb6d78e506844b3b96d5b35aa047fbbd>:0 
  at (wrapper remoting-invoke-with-check) Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake(Mono.Net.Security.AsyncOperationStatus)
  at Mono.Net.Security.AsyncHandshakeRequest.Run (Mono.Net.Security.AsyncOperationStatus status) [0x00006] in <fb6d78e506844b3b96d5b35aa047fbbd>:0 
  at Mono.Net.Security.AsyncProtocolRequest+<ProcessOperation>d__24.MoveNext () [0x000ff] in <fb6d78e506844b3b96d5b35aa047fbbd>:0 
--- End of stack trace from previous location where exception was thrown ---
  at Mono.Net.Security.AsyncProtocolRequest+<StartOperation>d__23.MoveNext () [0x0008b] in <fb6d78e506844b3b96d5b35aa047fbbd>:0 
   --- End of inner exception stack trace ---
  at Mono.Net.Security.MobileAuthenticatedStream+<ProcessAuthentication>d__47.MoveNext () [0x00254] in <fb6d78e506844b3b96d5b35aa047fbbd>:0 
   --- End of inner exception stack trace ---
  at System.Threading.Tasks.Task.ThrowIfExceptional (System.Boolean includeTaskCanceledExceptions) [0x00011] in <d4a23bbd2f544c30a48c44dd622ce09f>:0 
  at System.Threading.Tasks.Task.Wait (System.Int32 millisecondsTimeout, System.Threading.CancellationToken cancellationToken) [0x00043] in <d4a23bbd2f544c30a48c44dd622ce09f>:0 
  at System.Threading.Tasks.Task.Wait () [0x00000] in <d4a23bbd2f544c30a48c44dd622ce09f>:0 
  at M2Mqtt.Net.MqttNetworkChannel.Connect () [0x000a8] in <72fbe921f857483bafbb8b397ec98dd1>:0 
  at M2Mqtt.MqttClient.Connect (System.String clientId, System.String username, System.String password, System.Boolean willRetain, System.Byte willQosLevel, System.Boolean willFlag, System.String willTopic, System.String willMessage, System.Boolean cleanSession, System.UInt16 keepAlivePeriod) [0x0001e] in <72fbe921f857483bafbb8b397ec98dd1>:0 
   --- End of inner exception stack trace ---
  at M2Mqtt.MqttClient.Connect (System.String clientId, System.String username, System.String password, System.Boolean willRetain, System.Byte willQosLevel, System.Boolean willFlag, System.String willTopic, System.String willMessage, System.Boolean cleanSession, System.UInt16 keepAlivePeriod) [0x00037] in <72fbe921f857483bafbb8b397ec98dd1>:0 
  at M2Mqtt.MqttClient.Connect (System.String clientId) [0x00000] in <72fbe921f857483bafbb8b397ec98dd1>:0 
  at MqttDataServices.Services.MqttDataService+<Initialize>d__5.MoveNext () [0x00266] in C:\jstuff\MqttSample\MqttDataServices\Services\MqttDataService.cs:183 

我目前加载和访问X509证书的方式不安全或是最佳做法。有用。我希望最终能够学习如何访问每个移动平台的设备ca keystore。我使用cross-platform plug-in FilePicker加载证书，base64编码并保存。

 FileData fileData = await Plugin.FilePicker.CrossFilePicker.Current.PickFile();
 if (fileData == null)
 return; // user canceled file picking

 string fileName = fileData.FileName;
 string content = Convert.ToBase64String(fileData.DataArray, 0, fileData.DataArray.Length,
 Base64FormattingOptions.None);

 string deviceFileName = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), fileName);
 File.WriteAllText(deviceFileName, content);      

我通过推特联系了几个Xamarin人。我在上面提到的存储库中有一个open issue讨论问题，来自Microsoft的@baulig我相信给了我答案，但我目前不知道如何实现它。

我只看了证书验证码，它本质上是做什么的

var certStore = KeyStore.GetInstance ("AndroidCAStore");
  certStore.Load(null);

这是入口点：https://github.com/mono/mono/blob/master/mcs/class/System/Mono.Btls/MonoBtlsX509LookupAndroid.cs，它调用此代码https://github.com/mono/mono/blob/master/mcs/class/System/System/AndroidPlatform.cs#L101，然后调用xamarin-android代码：https://github.com/xamarin/xamarin-android/blob/master/src/Mono.Android/Android.Runtime/AndroidEnvironment.cs

KeyStore应该是这个类：https://developer.xamarin.com/api/type/Java.Security.KeyStore/。

所以你应该可以通过Java.Security.KeyStore这样做。

• 在AndroidManifest.xml中授予哪些权限？
• 我可以研究哪些术语来正确访问平台ca keystore？

首次发布后添加

• 2019年2月27日（MST）下午2:51 从MqttDataService.cs添加了证书和mqtt客户端创建

 X509Certificate caCert = X509Certificate.CreateFromCertFile(Path.Combine(filesDirectoryBasePath, "ca.crt"));
 string thePfxPathOnDevice = Path.Combine(filesDirectoryBasePath, "xamarinclient.pfx");
 string theBase64EncodedPfx = File.ReadAllText(thePfxPathOnDevice);

 byte[] certificate = Convert.FromBase64String(theBase64EncodedPfx);
 X509Certificate2 clientCert = new X509Certificate2(certificate, "xamarin");
 _client = new MqttClient(
     GetHostName(_xpdSetting.MqttBrokerAddress),
     Int32.Parse(_xpdSetting.MqttBrokerTlsPort),
     _xpdSetting.UseTls,
     caCert,
     clientCert,
     MqttSslProtocols.TLSv1_2
     //MyRemoteCertificateValidationCallback
     );

Answer 1

由于您使用的是.Net的/ Mono Socket（通过M2MqttDotnetCore），只需使用cert pinning，您只需要处理RemoteCertificateValidationCallback。因此，没有搞乱Android的可信商店等...

Android上的SslStream用法：

注意：在Android上存在SslStream的问题，对象分配可能会变得疯狂......我相信（？）这是一个未解决的问题。 （我不得不使用Java的SSLSocket几次来解决这个问题）

Enable Native TLS 1.2+

• 通过Android项目构建选项使用BoringSSL

Add your cert to the Android's Asset directory:

├── Assets
│   └── sushihangover.cert

• 这是你的cert / .pem文件（不是你的KEY！）
• 确保这是一个没有unicode BOM头的ascii文件
• 通过openssl示例（只需将其更改为主机和安全端口） echo -n | openssl s_client -connect 10.1.10.250:5001 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p'

RemoteCertificateValidationCallback Implementation

注意：以下代码可以在NetStd2.0或Xamarin.Android中使用

X509Certificate sushihangoverCert; // Class level var

bool CertificateValidation(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors certificateErrors)
{
    if (sushihangoverCert == null)
    {
        // There is no non-async version of OpenAppPackageFileAsync (via Xamarin.Essential) 😡 Why!!!
        using (var waitHandle = new EventWaitHandle(false, EventResetMode.AutoReset))
        {
            Task.Run(async () =>
            {
                using (var assetStream = await Xamarin.Essentials.FileSystem.OpenAppPackageFileAsync("sushihangover.cert"))
                using (var memStream = new MemoryStream())
                {
                    assetStream.CopyTo(memStream);
                    sushihangoverCert = new X509Certificate(memStream.ToArray());
                    waitHandle.Set();
                }
            });
            waitHandle.WaitOne();
        }
    }
    return sushihangoverCert.Equals(certificate) ? true : false;
}

SSLStream Usage Example:

注意：这是使用自签名证书连接到NetCore Web API端口

using (var tcpClient = new TcpClient("10.1.10.250", 5001))
using (var ssl = new SslStream(tcpClient.GetStream(), false, new RemoteCertificateValidationCallback(CertificateValidation)))
{
    ssl.AuthenticateAsClient("10.1.10.250", null, System.Security.Authentication.SslProtocols.Tls12, false);
    if (ssl.CanWrite)
    {
        var send = Encoding.ASCII.GetBytes("GET /api/item HTTP/1.1\r\nhost: 10.1.10.250\r\n\r\n");
        await ssl.WriteAsync(send, 0, send.Length);
        var buffer = new byte[4096];
        var count = await ssl.ReadAsync(buffer, 0, buffer.Length);
        Console.WriteLine(Encoding.UTF8.GetString(buffer, 0, count));
    }
    else
        throw new SocketException();
}

Server cert mismatch error:

如果您的服务器证书（自签名或不签名）与您固定的证书不一致，您将收到：

{Mono.Btls.MonoBtlsException: Ssl error:1000007d:SSL routines:OPENSSL_internal:CERTIFICATE_VERIFY_FAILED