c# - 无法使用 WebClient.DownloadFile 方法从启用了 TLS 1.1/1.2 协议(protocol)的计算机下载文件

Question

我正在尝试实现一个简单的控制台应用程序，以通过 TLS 1.1/1.2 协议(protocol)使用 Webclient.DownloadFile 方法下载文件。 这是应用程序的代码:

var downloadUrl = "https://serverURL.com/sample.mp3";
var filename = "sample.mp3";
var myWebClient = new WebClient();
myWebClient.DownloadFile(downloadUrl, filename);

每次我运行它都会收到以下错误消息:

Unhandled Exception: System.Net.WebException: 
The underlying connection was closed: An unexpected error occurred on a receive. --->   

System.ComponentModel.Win32Exception: The client and server cannot communicate, because they do not possessa common algorithm
at System.Net.SSPIWrapper.AcquireCredentialsHandle(SSPIInterface SecModule, String package, CredentialUse intent, SecureCredential scc)
at System.Net.Security.SecureChannel.AcquireCredentialsHandle(CredentialUse credUsage, SecureCredential& secureCredential)
at System.Net.Security.SecureChannel.AcquireClientCredentials(Byte[]& thumbPrint)
at System.Net.Security.SecureChannel.GenerateToken(Byte[] input, Int32 offset, Int32 count, Byte[]& output)
at System.Net.Security.SecureChannel.NextMessage(Byte[] incoming, Int32 offset, Int32 count)
at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Net.TlsStream.CallProcessAuthentication(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.ConnectStream.WriteHeaders(Boolean async)
--- End of inner exception stack trace ---
at System.Net.WebClient.DownloadFile(Uri address, String fileName)
at System.Net.WebClient.DownloadFile(String address, String fileName)
at web_downloader.Program.Main(String[] args) in c:\Users\user\Documents\Visual Studio 2013\Projects\web_downloader\web_downloader\Program.cs:line 27

我有以下设置:web_downloader 应用程序位于 ServerA(Windows Server 2012 R2/64 位)，它在 HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control 下的注册表项中具有以下内容/SecurityProviders/SCHANNEL/协议(protocol):

PCT 1.0
--Client
----DisabledByDefault=1
----Enabled=0
--Server
----DisabledByDefault=1
----Enabled=0
SSL 2.0
--Client
----DisabledByDefault=1
----Enabled=0
--Server
----DisabledByDefault=1
----Enabled=0
SSL 3.0
--Client
----DisabledByDefault=1
----Enabled=0
--Server
----DisabledByDefault=1
----Enabled=0
TLS 1.0
--Client
----DisabledByDefault=1
----Enabled=0
--Server
----DisabledByDefault=1
----Enabled=0
TLS 1.1
--Client
----DisabledByDefault=0
----Enabled=1
--Server
----DisabledByDefault=0
----Enabled=1
TLS 1.2
--Client
----DisabledByDefault=0
----Enabled=1
--Server
----DisabledByDefault=0
----Enabled=1

而存储sample.mp3文件的ServerB有以下内容:

SSL 2.0
  Client
    DisabledByDefault=1
TLS 1.1
  Client
    DisabledByDefault=0
    Enabled=1
  Server
    DisabledByDefault=0
    Enabled=1
TLS 1.2
  Client
    DisabledByDefault=0
    Enabled=1
  Server
    DisabledByDefault=0
    Enabled=1

一旦我在 ServerA 上启用 TLS 1.0，我就可以从 ServerB (Windows 7/64bit/Net Framework 4.5.1) 下载 mp3 文件，而无需任何问题。

系统加密:使用符合 FIPS 的算法进行加密、散列和签名策略在两台机器上都被禁用。

我是否缺少 DownloadFile 方法使用 TLS 1.1/1.2 的任何配置参数？

Answer 1

.NET Framework 使用自己的设置来决定默认使用哪个 HTTPS 版本。参见 https://stackoverflow.com/a/169396/126229在客户端上设置 ServicePointManager.SecurityProtocol 设置以确保它尝试协商 TLS1.1 连接。

您还可以使用 Fiddler 查看出站流量(查看 CONNECT 隧道的 TextView 请求检查器)以了解 ClientHello 消息的分割。请注意，在启用 HTTPS 解密的情况下运行 Fiddler 会产生干扰，因为 Fiddler 本身默认使用 SSL3+TLS1 与服务器通信。