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I develop a C# program in Visual Studio 2013 which communicates with a SOAP webservice. How can I tell which version of TLS my program uses?

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  • Wouldn't that be determined by the web server? Why do you need to know? Commented Oct 23, 2017 at 12:06
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    Check ServicePointManager.SecurityProtocol value for the supported protocols. Commented Oct 23, 2017 at 12:12
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    Just enable everything on ServicePointManager.SecurityProtocol and you're good to go, right? Commented Oct 23, 2017 at 12:12
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    @MickyD the server will refuse the connection if the runtime doesn't support 1.2. Commented Oct 23, 2017 at 12:26
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    @rene a couple of years ago several large service providers (think airlines) dropped even TLS1.1. A lot of companies had to scramble to upgrade to .NET 4.5.2 Commented Oct 23, 2017 at 12:28

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I got the answer by directing my program to make requests to https://www.howsmyssl.com/a/check.

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I like to test the behaviour of my program, not just to rely on the documentation.
I don't understand the disdain for this answer. It uses empirical testing and it can be generalized to other server types.
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TLS 1.2 was added in .NET 4.5. The earliest supported .NET version is 4.5.2, so you won't have any issues if you use a supported version.

.NET 4.6 uses TLS 1.2 by default. Earlier versions need this line to enable it :

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

TLS 1.0 is being phased out and SSL v3 is considered broken so they shouldn't be added.

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Can you link to a source confirming that .NET 4.6 uses TLS 1.2 by default? I can't find anything official and can see other commentors contradicting this e.g: stackoverflow.com/a/47913910/5344430
Don't use 4.6 to begin with, don't try to hard-code the versions. Simply googling for .NET TLS 1.2 returns Transport Layer Security (TLS) best practices with the .NET Framework as the first result. Use .NET 4.7 on a supported OS and let your application use the best available TLS version. Even 4.6.2 was a bit of a mess both on TLS and assembly redirects.
I'm not going to use 4.6. I literally just want to know where you got the information "4.6 uses TLS 1.2 by default" because I couldn't find it anywhere. How did you confirm / prove that?
I posted the link already. 3 years ago I was answering the question How can I tell which version of TLS my program uses? and the answer isn't VS 2013. To get TLS 1.2 without code modifications you need 4.6 at least. By that point I had answered that question dozens of times for years and didn't bother posting another full explanation. By that point (like many common questions in SO) just finding a good duplicate would take more time than writing a quick answer
@alksdjg and, the real question after all was posted as a comment to Oria's answer As my production web service calls were communicating with a 3rd party service, I needed an extra proof of which protocol was being used before and after I made the .net version change.
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Another good way to check is to install WireShark (https://www.wireshark.org/download.html)

and to use it while running your application. within the TLS Packets you will be able to see versions and such:

Example for Wireshark View Of TLS traffic...

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There's no reason to. There's no ambiguity. 4.6 -> TLS1.2 by default 4.5 -> TLS11 and config change for 1.2. 4 and below, no TLS 1.2
4 and below support TLS 1.2 with a hotfix.
3.5: support.microsoft.com/en-us/help/3154520/…
4.0: blogs.msdn.microsoft.com/saurabs/2017/06/01/…
@jessehouwing even worse, these hotfixes depend on some well-known hacks to work in code, like assigning the enum's value to SecurityProtocol even though it isn't defined. That was used as a stopgap 2 years ago, when the providers started demanding TLS1.2
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