How to make .Net 4.0 & 4.5 use TLS 1.2

Basics of HTTP(S)

Unless its not for fun, all the web sites need to be hosted using http(s). Is http(s) that much important? I will say yes. Otherwise, there are chances that our site will be viewed by people with different content than what we published. The web page is not directly sent from webserver to the client computer. It goes through various devices which can manipulate the content inside the site. eg: I as a free Wi-Fi provider can inject my own ads into the sites if they are simply using plain http connection. There were incidents happened as well.

Yes, it is important to have our web site served via http(s) to make sure our customers are seeing what we are sending them. How http(s) is solving this. Simply saying, it uses encryption when the web page contents are transmitted. So no one can see the content who has access to the intermediate devices. Even if they inject some content, it won't get displayed in our browser as the browser will not be able to decrypt the modified contents.

People who are curious about internal will have many questions by now. If our browser for example Chrome can decrypt the content why can't someone who has Chrome browser source code decrypt the same to see the contents?

Welcome to the world of security!!! There are concepts of encryption keys. Only people with the key can decrypt the encrypted content. Ok in this case if we have the key to decrypt the contents why can the attacker obtain the same key from the webserver by accessing the same site from the browser? That is solved with key exchange and usage of asymmetric and symmetric encryptions wisely. What is the key exchange? It is a sequence of steps involved to establish communication between 2 parties and here its web server and the client browser. This process is called the secure HTTP protocol.

Its enough and getting more complicated. Interested readers can please go through the links below to understand it more. 

Others just continue on the assumption that http(s) is the silver bullet to make sure what our viewers seeing is what we sent from the server.

Versions of http(secure)

Ensuring security is always a continuous process. There are chances that there may be a new flaw in the protocol in the future and we need to fix that issue. It becomes the next version of the protocol. When the issue is fixed by specs the existing web servers and browsers also needs to be fixed and it leads to their next version or patch. 

But can we expect all the people in the world update their browser as soon as the new fixed version or patch is released? Can the new fixed browsers assume that all the web servers its communicated are updated with the latest protocol version? Absolutely no. This requires different versions of this communication protocol to be live side by side in the internet. It is the duty of the communicators to settle in what protocol to be used. When we say protocol it includes the encryption details, key exchange details, etc...

Wiki will give more details on secure HTTP versions and the latest as of today is TLS 1.2 and TLS 1.3 is in the draft.

Fallbacks

As we saw earlier, https is a protocol before starting both parties involved in communication needs to agree on the method. It is not much complicated. Obviously, one party needs to tell that what it is supported and the server selects the latest technique. Though one party is capable of using the latest protocol, it may not use that as the other end doesn't know and this is called fallback.

Check what is our client browser is using

We saw that http(s) will solve a big security issue. It needs a server-side webserver software and client-side browser software who understands the encryption algorithms. Also, it is versioned

Is our browser capable of working with latest http(s) which is TLS 1.2? Just browse to the below URL to see what is the protocols supported in our browser.

https://www.howsmyssl.com/

They provide API as well which our application can call and understand what it can support. We will be seeing how an application can check this shortly

https://www.howsmyssl.com/a/check

Check whether the web site is using SSL/TLS?

Similarly, if we want to check whether a particular site is using secure HTTP go to below URL and enter the web site URL.

https://www.ssllabs.com/ssltest/

Tools to inspect the network communication

If we want to ensure the protocol at the low levels of the system, we can use tools such as Wireshark and all. Those tools help us to inspect the messages in the byte level.

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How to host a web site in https

Whatever we discussed above was all general and nothing related to software development. Let's see how a web site can be hosted with a secure HTTP protocol.

The basic need for this is a certificate which is used as a key in encryption. We can create a self sighed certificate or buy from the certificate-issuing authority. Once we have the certificate, it can be associated with our web site via the web server. How to associate the certificate with web site changes from technology to technology.  Below is a link which explains how a site can be hosted securely using https protocol in IIS web server.

http://www.codeproject.com/Tips/722979/Setting-up-IIS-with-HTTPS-Binding

How to access SSL site from .Net

We can write applications which can request web sites for web pages as well as data in the same way browser application is requesting data. In Microsoft .Net there are many ways such as WebClient, WCF etc...

Below is the code which can be used to access https://www.howsmyssl.com API from C#.Net application.

var response = WebRequest.Create("https://www.howsmyssl.com/a/check").GetResponse();
var responseData = new StreamReader(response.GetResponseStream()).ReadToEnd();
Console.WriteLine(responseData);

On console we can see response similar to this.

Hosting WCF Service using http(s)

Hosting WCF using http(s) is not much different than hosting a web site using https. Differences mainly include changes in the web.config file to use Transport security. Below is a link which explains how we can host a WCF web service via http(s)

https://msdn.microsoft.com/en-us/library/Hh556232(v=VS.110).aspx

Accessing HTTP(s) WCF Service from .Net client

Similarly when we are consuming WCF service hosted via https, we need to make sure the service client is configured to use Transport security. Below link explains how a .Net client can access http WCF service. Just change the binding security to Transport in web.config



https://msdn.microsoft.com/en-us/library/bb386386.aspx

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Why TLS 1.2

Let's come to TLS 1.2. As we have seen above, the latest version of the secure HTTP protocol is TLS 1.2. It means there were problems in earlier versions and its fixed in 1.2. So we need to make sure that as a security-conscious user our browsers need to be upgraded to support TLS 1.2. Will upgrading browser make sure all the connections are using TLS 1.2 protocol? 

No, if we are accessing a web site which is hosted in an environment without TLS 1.2, our browser will fall back to an older protocol version. If we want to avoid falling back to TLS 1.2, we can change the settings in all modern browsers such as Chrome, Firefox and IE to always use TLS 1.2 and that is recommended.

More interested readers can google and see what are the changes happened in TLS 1.2 which is based on TLS 1.1.

https://casecurity.org/2013/09/19/its-time-for-tls-1-2/

Obviously, as a responsive software engineer, we should make sure all our web applications must be supporting TLS 1.2 which is the latest at this moment. Need to use proper web servers and technologies to support the same. If we are not moving with the crowd it is very difficult to sustain in the market.

Enable TLS 1.2 at OS level

Not every windows operating system is equipped with TLS 1.2 by default. Below is a link explains how to enable TLS 1.2 in Windows 2008R2, Windows 7 and IIS 7.5. I believe people are still using these versions. 

http://www.derekseaman.com/2010/06/enable-tls-12-aes-256-and-sha-256-in.html
http://tecadmin.net/enable-tls-on-windows-server-and-iis/

In Windows Server 2012 & Windows 8.1 TLS 1.2 is enabled by default.

Not that this will make sure the TLS 1.2 is enabled at the OS level. Also, the default apps such as IIS web server and IE browser will also follow the same protocol by default. Basically, there is a system-level dll called schannel.dll which is responsible for this secure communication and applications are calling the API provided by it to have secure communication. Obviously, there are applications which are not replying on schannel to do communication. eg: Chrome and Firefox are not using this schannel so they can use TLS 1.2 even when they are running inside Windows Vista.

Similarly, when we say Windows Vista, 2008 and below are not supporting TLS 1.2, we should understand that their schannel.dll doesn't have support for the protocol.

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TLS 1.2 and Microsoft.Net

Now let's focus on using TLS 1.2 in the .Net world. We need to make sure that the web sites are served via TLS 1.2 protocol and client apps which are consuming the same need to support TLS 1.2. .Net is running on top of the operating system and mostly its windows. If host windows support TLS 1.2 .Net can also support TLS 1.2 as it relies on schannel.dll¹

The first task here is to make sure we are using the right tools and technologies.

TLS 1.2 and .Net Framework 4.5

.Net is also versioned. Versions below 4.5 don't know how to communicate via TLS 1.2.In .Net 4.5 the TLS 1.2 is enabled by default. Simply compile our applications in, Net 4.5 and we will get TLS 1.2 communication for our applications.

How to make .Net 4.0 app talk using TLS 1.2

Technically speaking just recompile the existing older application to .Net 4.5 to get TLS 1.2 support. It sounds simple as everybody expecting that there are no breaking changes in .Net 4.5 and our application will function as is. But if we are serious about delivering quality software we also need to test the entire app in 4.5 before shipping. It really adds cost.

Let's see if there are any ways to use TLS 1.2 by .Net 4.0 apps.

System.dll overwrite

When we install .Net 4.5 its basically adding changes on top of .Net 4.0. In other words, the System.dll used for 4.0 apps will be overwritten to 4.5 version of System.dll. So there are possibilities that .Net 4.0 apps will execute 4.5 code when they access functions in System.dll. Which means if we have .Net 4.5 installed in the machine where our .Net 4.0 is running it can take advantage of TLS1.2. All our solutions below are depending on this factor.

Below links explains the .Net versioning and overwriting.

http://blogs.msdn.com/b/rodneyviana/archive/2014/12/23/identifying-the-net-version-you-are-running-2-0-4-5-4-5-1-or-4-5-2.aspx

https://weblog.west-wind.com/posts/2012/Mar/13/NET-45-is-an-inplace-replacement-for-NET-40

1. Code change in 4.0 to use TLS 1.2

Now its the matter of changing the default protocol used by 4.0 to TLS 1.2. This can be done by forcefully changing the protocol as below.

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;//SecurityProtocolType.Tls1.2;

If we look at the SecurityProtocolType enum for .Net 4.0, we will not be able to see the TLS1.2. But in 4.5 we can see that. So .Net 4.0 will not compile if we use TLS1.2 enum value. But if we use the TLS1.2 enum number it will compile and at runtime since the .Net 4.0's System.dll is replaced with 4.5 the cast will work. 

Please note that this will fail if we are running the same app in a machine which don't have 4.5 installed. Recommended only for servers where its easy to manage the .Net version.

2. Registry change to force .Net 4.0 to use TLS 1.2

If we inspect the .Net 4.5 ServicePointManager source code we can see that the default protocol is depending on the below registry entry.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319: SchUseStrongCrypto to DWORD 1

The default value will be 0. Simply change this to 1 to get .Net 4.5 System.dll use TLS 1.2. Since our 4.0 application uses 4.5 System.dll 4.0 gets TLS 1.2 support.

http://stackoverflow.com/questions/28286086/default-securityprotocol-in-net-4-5

Update 22May2019

Below is the Microsoft official link on .Net and TLS. It talks about .Net 4.7 as well.
https://docs.microsoft.com/en-us/dotnet/framework/network-programming/tls

References

https://www.owasp.org/index.php/Transport_Layer_Protection_Cheat_Sheet#Client_.28Browser.29_Configuration
https://www.simple-talk.com/dotnet/.net-framework/tlsssl-and-.net-framework-4.0/
https://msdn.microsoft.com/en-us/library/system.security.authentication.sslprotocols(v=vs.110).aspx
https://istlsfastyet.com/
http://blogs.msdn.com/b/benjaminperkins/archive/2014/11/04/using-tls-1-2-with-wcf.aspx
http://blogs.msdn.com/b/benjaminperkins/archive/2011/10/07/secure-channel-compatibility-support-with-ssl-and-tls.aspx
http://www.dotnetnoob.com/2013/10/hardening-windows-server-20082012-and.html

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¹ - This is as of my understanding. Was not able to get any authentic links.
*-As far as my understanding TLS 1.2 support came from .Net 4.5. I am using 4.5.2 currently.