I had the same error message while scaffolding Identity to my ASP.NET Core MVC project. Since my connection was not behind a proxy, removing/editing proxy configurations didn't make sense. And I didn't want to delete a file or uninstall PMC either. While looking around I realized a "Clear All Nuget Cache(s)" button on Tools --> Options --> NuGet Package Manager --> General. After pressing the button I had to wait for some time for the operation to complete. After that I tried to scaffold the Identity again but it didn't work. Then I decided to restart VS and voila :)

安装小提琴也给我带来了类似的问题。卸载fiddler并从机器中删除fiddler代理。config(来自Framework和Framework64)解决了这个问题。

nuget restore 

and

msbuild /t:restore

两者都没有为我工作，因为同样的错误。但

dotnet restore 

完美的工作。试试

好吧，我尝试了上面所有的答案，希望我的注册表现在不是软管。但这似乎解决了我的问题:

https://learn.microsoft.com/en-us/answers/questions/959588/visual-studio-2022-won39t-connect-to-nuget.html

添加这个:TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

到this中逗号分隔的字符串:

微软HKLM \ SOFTWARE \政策\ \ SSL加密\ Configuration \ \ 00010002

我希望这能帮助下一个希望在周六早上快速进行有趣的概念验证，然后花3个小时寻找解决方案的人!!

我在Visual Studio 2015上执行Install-Package Modernizr时遇到了类似的问题。我通过以下步骤解决了这个问题:

Download the package from its online source. Go to Tools/NuGet Package Manager/Package Manager Settings. Select Package Sources from the window. Add a new package source by clicking on the + sign. Enter a name and source location by clicking on ... (triple dot) sign. Make sure that only the package source that you've just added is checked. Uncheck all the other package sources. Go to Package Manager Console and type Install-Package Modernizr. Visual Studio 2015 installs the package automatically and creates Scripts and packages folders in your root folder.

我希望同样的解决方案在安装其他包时也能起作用。

新包管理器的开发人员在2019年建议禁用tls 1.3作为解决方案(见第7705期)。

通过按Win + R打开注册表编辑器，并键入regedit Enter

导航到:

\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.3\Client

将“DisabledByDefault key 0”的值修改为1

然后重新启动Visual Studio。

在维基百科上阅读更多关于TLS的信息 阅读更多关于问题7705 w.r.t. NuGet在github

第三方编辑

请注意，这将禁用操作系统的tls 1.3，而不仅仅是对nuget或dotnet。 Windows 10 1909版确实包含TLS 1.3的实验性实现，但后续版本应该没问题。基于无法浏览nuget包的一个答案，您可以通过控制台程序测试tls是否存在问题

static async Task Main(string[] args)
{
    var client = new HttpClient();
    string uri = "https://apiint.nugettest.org/v3-index/index.json";
    var response = await client.GetAsync(uri);
    string msg = "If you see this, your machine has no TLS/SSL issues with nuget.org";
    Console.WriteLine(msg);

}