The client and server cannot communicate, because they do not possess a common algorithm - ASP.NET C# IIS TLS 1.0 / 1.1 / 1.2 - Win32Exception

I have an issue with a C# PayTrace Gateway. The below code was working fine until yesterday when I believe they turned off SSL3 due to the Poodle Exploit. When running the code below we got the following message. The remote server has forcefully closed the connection. After doing some research on the problem we determined that because our IIS Server 7.5 was configured to still use SSL3, C# defaulted to SSL3, which PayTrace would forcibly close the connection. We then removed SSL3 from the server. Which then lead to the following error:

The client and server cannot communicate, because they do not possess a common algorithm.

My guess is that there are additional SSL algorithm we need to install on the server now that SSL 3 is removed. Our IT staff claims that TLS 1.1 and TLS 1.2 are working and that ASP.NET should be now defaulting to those. But I feel like there still must be something else we need to install on the server, I have no knowledge of SSL Algorithms so I have no idea where to begin.

var postUrl = new StringBuilder();

//Initialize url with configuration and parameter values...
postUrl.AppendFormat("UN~{0}|", this.MerchantLoginID);
postUrl.AppendFormat("PSWD~{0}|", this.MerchantTransactionKey);
postUrl.Append("TERMS~Y|METHOD~ProcessTranx|TRANXTYPE~Sale|"); 
postUrl.AppendFormat("CC~{0}|", cardNumber);
postUrl.AppendFormat("EXPMNTH~{0}|", expirationMonth.PadLeft(2, '0'));
postUrl.AppendFormat("EXPYR~{0}|", expirationYear);
postUrl.AppendFormat("AMOUNT~{0}|", transactionAmount);
postUrl.AppendFormat("BADDRESS~{0}|", this.AddressLine1);
postUrl.AppendFormat("BADDRESS2~{0}|", this.AddressLine2);
postUrl.AppendFormat("BCITY~{0}|", this.City);
postUrl.AppendFormat("BSTATE~{0}|", this.State);
postUrl.AppendFormat("BZIP~{0}|", this.Zip);
postUrl.AppendFormat("SADDRESS~{0}|", this.AddressLine1);
postUrl.AppendFormat("SADDRESS2~{0}|", this.AddressLine2);
postUrl.AppendFormat("SCITY~{0}|", this.City);
postUrl.AppendFormat("SSTATE~{0}|", this.State);
postUrl.AppendFormat("SZIP~{0}|", this.Zip);
if (!String.IsNullOrEmpty(this.Country))
{
    postUrl.AppendFormat("BCOUNTRY~{0}|", this.Country);
}
if (!String.IsNullOrEmpty(this.Description))
{
    postUrl.AppendFormat("DESCRIPTION~{0}|", this.Description);
}
if (!String.IsNullOrEmpty(this.InvoiceNumber))
{
    postUrl.AppendFormat("INVOICE~{0}|", this.InvoiceNumber);
}
if (this.IsTestMode)
{
    postUrl.AppendFormat("TEST~Y|");
}

//postUrl.Append();

WebClient wClient = new WebClient();
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
String sRequest = "PARMLIST=" + Url.Encode(postUrl.ToString());
wClient.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
string sResponse = "";
sResponse = wClient.UploadString(PayTraceUrl, sRequest);

Also, just an FYI, this issue is also happening when we connect to First Data E4 gateway so it's not just a PayTrace thing. My guess is that as more gateways turn off access to SSL3 we'll continue to run into issues with other gateways until this can be resolved on the server. Also, I did find a few suggestions online, some suggested placing the following code right before making the outbound request:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

Unfortunately that did not work either, same error. Which is why I'm thinking something additional needs to be installed on the IIS7.5 server. I'm just not sure what.

There are several other posts about this now and they all point to enabling TLS 1.2. Anything less is unsafe.

You can do this in .NET 3.5 with a patch.
You can do this in .NET 4.0 and 4.5 with a single line of code

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12; // .NET 4.5
ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072; // .NET 4.0

In .NET 4.6, it automatically uses TLS 1.2.

See here for more details: .NET support for TLS.

In my case, even though Target Framework of Project was 4.7.1, I was still getting same Error, Solution was to change httpRuntime in web.config under system.web to 4.7.1!

In a previous answer, it was suggested to use this line of code for .Net 4.5:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12; // .NET 4.5

I would encourage you to OR that value in to whatever the existing values are like this:

ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12; // .NET 4.5

If you look at the list of values, you notice that they are a power of two. This way, in the future when things shift to TLS 2.0 for example, your code will still work.

There are two possible scenario, in my case I used 2nd point.

1. If you are facing this issue in production environment and you can easily deploy new code to the production then you can use of below solution.

   You can add below line of code before making api call,

   ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12; // .NET 4.5

2. If you cannot deploy new code and you want to resolve with the same code which is present in the production, then this issue can be done by changing some configuration setting file. You can add either of one in your config file.

<runtime>
    <AppContextSwitchOverrides value="Switch.System.Net.DontEnableSchUseStrongCrypto=false"/>
  </runtime>

or

<runtime>
  <AppContextSwitchOverrides value="Switch.System.Net.DontEnableSystemDefaultTlsVersions=false"/>
</runtime>

This was resolved. It turns out our IT Staff was correct. Both TLS 1.1 and TLS 1.2 were installed on the server. However, the issue was that our sites are running as ASP.NET 4.0 and you have to have ASP.NET 4.5 to run TLS 1.1 or TLS 1.2. So, to resolve the issue, our IT Staff had to re-enable TLS 1.0 to allow a connection with PayTrace.

So in short, the error message, "the client and server cannot communicate, because they do not possess a common algorithm", was caused because there was no SSL Protocol available on the server to communicate with PayTrace's servers.

UPDATE: Please do not enable TLS 1.0 on your servers, this was a temporary fix and is not longer applicable since there are now better work-arounds that ensure strong security practices. Please see accepted answer for a solution. FYI, I'm going to keep this answer on the site as it provides information on what the problem was, please do not down-vote.

Enabling TLS 1.0 solved our issues as well (after disabling SSL v3). (Server 2012 R2 with ASP.net 4.0 website processing against PPI pay services). This is the RegEdit script I used to set everything the way I wanted. We only disabled SSL v3 for the Client and not the server as doing that broke other things that we were not ready to deal with yet. After we upgrade the site to .Net 4.5.2 then we will disable TLS 1.0 again.

This script enables all protocols, Server and Client except for SSL v3 for the Client.

> Be sure to backup your registry!

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Client]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Client]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Client]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Client]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Client]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server]
"DisabledByDefault"=dword:00000000

My app is running in .net 4.7.2. Simplest solution was to add this to the config:

  <system.web>
    <httpRuntime targetFramework="4.7.2"/>
  </system.web>

In my case I solved the problem by enabling the last TLS version in the .Net Framework as explained in this article:

https://docs.microsoft.com/dotnet/framework/network-programming/tls

set these registry keys:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319] "SystemDefaultTlsVersions"=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319] "SystemDefaultTlsVersions"=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319] "SchUseStrongCrypto"=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319] " SchUseStrongCrypto"=dword:00000001

There are a couple of things that you need to check related to this.

Whenever there is an error like this thrown related to making a secure connection, try running a script like the one below in Powershell with the name of the machine or the uri (like "www.google.com") to get results back for each of the different protocol types:

 function Test-SocketSslProtocols {
    
    [CmdletBinding()] 
    param(
        [Parameter(Mandatory=$true)][string]$ComputerName,
        [int]$Port = 443,
        [string[]]$ProtocolNames = $null
        )

    #set results list    
    $ProtocolStatusObjArr = [System.Collections.ArrayList]@()


    if($ProtocolNames -eq $null){

        #if parameter $ProtocolNames empty get system list
        $ProtocolNames = [System.Security.Authentication.SslProtocols] | Get-Member -Static -MemberType Property | Where-Object { $_.Name -notin @("Default", "None") } | ForEach-Object { $_.Name }

    }
 
    foreach($ProtocolName in $ProtocolNames){

        #create and connect socket
        #use default port 443 unless defined otherwise
        #if the port specified is not listening it will throw in error
        #ensure listening port is a tls exposed port
        $Socket = New-Object System.Net.Sockets.Socket([System.Net.Sockets.SocketType]::Stream, [System.Net.Sockets.ProtocolType]::Tcp)
        $Socket.Connect($ComputerName, $Port)

        #initialize default obj
        $ProtocolStatusObj = [PSCustomObject]@{
            Computer = $ComputerName
            Port = $Port 
            ProtocolName = $ProtocolName
            IsActive = $false
            KeySize = $null
            SignatureAlgorithm = $null
            Certificate = $null
        }

        try {

            #create netstream
            $NetStream = New-Object System.Net.Sockets.NetworkStream($Socket, $true)

            #wrap stream in security sslstream
            $SslStream = New-Object System.Net.Security.SslStream($NetStream, $true)
            $SslStream.AuthenticateAsClient($ComputerName, $null, $ProtocolName, $false)
         
            $RemoteCertificate = [System.Security.Cryptography.X509Certificates.X509Certificate2]$SslStream.RemoteCertificate
            $ProtocolStatusObj.IsActive = $true
            $ProtocolStatusObj.KeySize = $RemoteCertificate.PublicKey.Key.KeySize
            $ProtocolStatusObj.SignatureAlgorithm = $RemoteCertificate.SignatureAlgorithm.FriendlyName
            $ProtocolStatusObj.Certificate = $RemoteCertificate

        } 
        catch  {

            $ProtocolStatusObj.IsActive = $false
            Write-Error "Failure to connect to machine $ComputerName using protocol: $ProtocolName."
            Write-Error $_

        }   
        finally {
            
            $SslStream.Close()
        
        }

        [void]$ProtocolStatusObjArr.Add($ProtocolStatusObj)

    }

    Write-Output $ProtocolStatusObjArr

}

Test-SocketSslProtocols -ComputerName "www.google.com"

It will try to establish socket connections and return complete objects for each attempt and successful connection.

After seeing what returns, check your computer registry via regedit (put "regedit" in run or look up "Registry Editor"), place

Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL

in the filepath and ensure that you have the appropriate TLS Protocol enabled for whatever server you're trying to connect to (from the results you had returned from the scripts). Adjust as necessary and then reset your computer (this is required). Try connecting with the powershell script again and see what results you get back. If still unsuccessful, ensure that the algorithms, hashes, and ciphers that need to be enabled are narrowing down what needs to be enabled (IISCrypto is a good application for this and is available for free. It will give you a real time view of what is enabled or disabled in your SChannel registry where all these things are located).

Also keep in mind the Windows version, DotNet version, and updates you have currently installed because despite a lot of TLS options being enabled by default in Windows 10, previous versions required patches to enable the option.

One last thing: TLS is a TWO-WAY street (keep this in mind) with the idea being that the server's having things available is just as important as the client. If the server only offers to connect via TLS 1.2 using certain algorithms then no client will be able to connect with anything else. Also, if the client won't connect with anything else other than a certain protocol or ciphersuite the connection won't work. Browsers are also something that need to be taken into account with this because of their forcing errors on HTTP2 for anything done with less than TLS 1.2 DESPITE there NOT actually being an error (they throw it to try and get people to upgrade but the registry settings do exist to modify this behavior).

After messing with this for days, my final fix for our issues required two things;

1. We added this line of code to all of our .Net libraries that make out bound api calls to other vendors that had also disabled their SSL v3.

   ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls; // (.Net 4 and below)

2. This is the final and FULL registry changes you will need when you are running ASP.Net 4.0 sites and will need to be slightly changed after you upgrade to ASP.Net 4.5.

After we rebooted the servers - all problems went away after this.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Client]
"DisabledByDefault"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Client]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Server]
"DisabledByDefault"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Server]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Client]
"DisabledByDefault"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Client]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server]
"DisabledByDefault"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Client]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Client]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Client]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Client]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client]
"DisabledByDefault"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server]
"Enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server]
"DisabledByDefault"=dword:00000000

I fixed this error by upgrading the app from .Net Framework 4.5 to 4.6.2.

TLS-1.2 was correctly installed on the server, and older versions like TLS-1.1 were disabled. However, .Net 4.5 does not support TLS-1.2.

In previous answers a few registry keys that might not exist are missed. They are SchUseStrongCrypto that must exist to allow to TLS protocols work properly.

After the registry keys have been imported to registry it should not be required to make changes in code like

> ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

Below there are all registry keys and values that are needed for x64 windows OS. If you have 32bit OS (x86) just remove the last 2 lines. TLS 1.0 will be disabled by the registry script. Restarting OS is required.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Client]
"DisabledByDefault"=dword:00000001
"enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\server]
"disabledbydefault"=dword:00000001
"enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\ssl 3.0]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\ssl 3.0\client]
"disabledbydefault"=dword:00000001
"enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\ssl 3.0\server]
"disabledbydefault"=dword:00000001
"enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.0]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.0\client]
"disabledbydefault"=dword:00000001
"enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.0\server]
"disabledbydefault"=dword:00000001
"enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.1]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.1\client]
"disabledbydefault"=dword:00000000
"enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.1\server]
"disabledbydefault"=dword:00000000
"enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.2]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.2\client]
"disabledbydefault"=dword:00000000
"enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.2\server]
"disabledbydefault"=dword:00000000
"enabled"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319]
"SchUseStrongCrypto"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319]
"SchUseStrongCrypto"=dword:00000001