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I'm trying to establish SSL/TLS connection to test server with self-signed certificate. Communication through unsecure channel worked without issues.

Here is my sample code, which I've written based on this solutions: Allowing Untrusted SSL Certificates with HttpClient C# Ignore certificate errors? .NET client connecting to ssl Web API

ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true; var c = new HttpClient(); var r = c.GetAsync("https://10.3.0.1:8443/rest/v1").Result; if (r.IsSuccessStatusCode) { Log.AddMessage(r.Content.Get<string>()); } else { Log.AddMessage(string.Format("{0} ({1})", (int)r.StatusCode, r.ReasonPhrase)); }

also tried this:

var handler = new WebRequestHandler(); handler.ServerCertificateValidationCallback = delegate { return true; }; var c = new HttpClient(handler); ...

and this

ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

but each time I've got an exception:

InnerException: System.Net.Http.HttpRequestException _HResult=-2146233088 _message=An error occurred while sending the request. HResult=-2146233088 IsTransient=false Message=An error occurred while sending the request. InnerException: System.Net.WebException _HResult=-2146233079 _message=The request was aborted: Could not create SSL/TLS secure channel. HResult=-2146233079 IsTransient=false Message=The request was aborted: Could not create SSL/TLS secure channel. Source=System StackTrace: at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) at System.Net.Http.HttpClientHandler.GetResponseCallback(IAsyncResult ar) InnerException:

What do I do wrong? Why I can't connect to this server (which has invalid-self-signed certificate)

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10 Answers 10

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202

You are doing it right with ServerCertificateValidationCallback. This is not the problem you are facing. The problem you are facing is most likely the version of SSL/TLS protocol.

For example, if your server offers only SSLv3 and TLSv10 and your client needs TLSv12 then you will receive this error message. What you need to do is to make sure that both client and server have a common protocol version supported.

When I need a client that is able to connect to as many servers as possible (rather than to be as secure as possible) I use this (together with setting the validation callback):

 ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
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11 Comments

I have a similar issue. Because of the POODLE-attack we are forced to shut down TLS 1.0 on our server. When I do this, a third-party app stops working. Decompiling the assambly shows a code similar to yours. It uses webclientc.SendAsync instead of GetAsync. If I copy the code to a consoleapp for testing I can reproduce the error, and by adding ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 it works. I tought that there would be some kind of handshake between server and Client to uncover what TLS version to use? Why doesn't it automatically choose 1.1 when 1.0 is disabled?
Thanks! Was struggling 3 hours with this. Adding this line did it for me: ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
Note that newer version of .NET has this enabled by default, all we needed to do is to set .NET version to 4.6.1
It means exactly that, valid or not, you don't care. That callback allows you to simply avoid any security checks on that certificate.
Great answer, I feel like this ServicePointManager.SecurityProtocol value should maybe be the default. Or at least that there should be more insight directly inside the thrown Exception.
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We have been solving the same problem just today, and all you need to do is to increase the runtime version of .NET

4.5.2 didn't work for us with the above problem, while 4.6.1 was OK

If you need to keep the .NET version, then set

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
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2 Comments

Which of the variants you used and how exactly?
I have a .NET 4.5 application that starting from today, won't work with a specific SSL site. If I change to 4.6.1 it works fine, but I can't really change. I'm not sure what is there to be done :|
19

Just as a follow up for anyone still running into this – I had added the ServicePointManager.SecurityProfile options as noted in the solution:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

And yet I continued to get the same “The request was aborted: Could not create SSL/TLS secure channel” error. I was attempting to connect to some older voice servers with HTTPS SOAP API interfaces (i.e. voice mail, IP phone systems etc… installed years ago). These only support SSL3 connections as they were last updated years ago.

One would think including SSl3 in the list of SecurityProtocols would do the trick here, but it didn’t. The only way I could force the connection was to include ONLY the Ssl3 protocol and no others:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;

Then the connection goes through – seems like a bug to me but this didn’t start throwing errors until recently on tools I provide for these servers that have been out there for years – I believe Microsoft has started rolling out system changes that have updated this behavior to force TLS connections unless there is no other alternative.

Anyway – if you’re still running into this against some old sites/servers, it’s worth giving it a try.

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We have a CUCMPowerShell module for using the Cisco Unified Communications AXL api via PowerShell and your answer helped us get this fixed by adding [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType]::Ssl3. Thank you! Full code can be seen in the Invoke-CUCMSOAPAPIFunction
@Jeff - Check out the linked article. I think it may explain why Ssl3 did not work and suggests two ways to re-enable Ssl3. learn.microsoft.com/en-us/dotnet/framework/migration-guide/…
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I'm using .NET version 4.8 and specifying the SSL protocol during the initialization of the HttpClient worked for me to resolve this issue, as shown below.

var client = new HttpClient(new HttpClientHandler { SslProtocols = SslProtocols.Tls12});
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This is much better answer than setting the "ServicePointManager.SecurityProtocol" since application can have multiple httpClients communicating with different apis etc so you might want/need different setting for each of them. This should be the accepted answer.
This was great thank you. Works for .NET 4.6 and 4.7 too in case anyone using lower versions
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move this line: ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

Before this line: HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);

Original post: KB4344167 security update breaks TLS Code

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After trying all of the above to no avail, this was the answer: the ServicePointManager needs to be set before creating the HttpWebRequest.
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In my case TLS1_2 was enabled both on client and server but the server was using MD5 while client disabled it. So, test both client and server on http://ssllabs.com or test using openssl/s_client to see what's happening. Also, check the selected cipher using Wireshark.

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TLS 1.0 and 1.1 are now End of Life. A package on our Amazon web server updated, and we started getting this error.

The answer is above, but you shouldn't use tls or tls11 anymore.

Specifically for ASP.Net, add this to one of your startup methods.

 public Startup() { ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12;

but I'm sure that something like this will work in many other cases.

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I came across this thread because I also had the error Could not create SSL/TLS secure channel. In my case, I was attempting to access a Siebel configuration REST API from PowerShell using Invoke-RestMethod, and none of the suggestions above helped.

Eventually I stumbled across the cause of my problem: the server I was contacting required client certificate authentication.

To make the calls work, I had to provide the client certificate (including the private key) with the -Certificate parameter:

$Pwd = 'certificatepassword' $Pfx = New-Object -TypeName 'System.Security.Cryptography.X509Certificates.X509Certificate2' $Pfx.Import('clientcert.p12', $Pwd, 'Exportable,PersistKeySet') Invoke-RestMethod -Uri 'https://your.rest.host/api/' -Certificate $Pfx -OtherParam ...

Hopefully my experience might help someone else who has my particular flavour of this problem.

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If will work perfect if you specify only TLS in security protocol.

try { ServicePointManager.Expect100Continue = true; ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12; ServicePointManager.ServerCertificateValidationCallback = delegate { return true; }; var webClient = new WebClient(); var s = webClient.DownloadString("https://google.com"); Console.WriteLine(s); } catch (Exception ex) { Console.WriteLine(ex); } Console.ReadLine();
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Hello and welcome to StackOverflow! Please provide more details as to what your code does, and why does it answer the question.
Actually some frameworks does not use other security protocols so you need to specify TLS.
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If you use .net framework 4.0 use the below line

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

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