Posts Tagged ‘TLS’

Using TLS 1.2 with SMTP

Tuesday, July 2nd, 2019

By default most systems allow SSL 3.0, TLS 1.0, 1.2 and 1.2 to be used, when connecting using SMTP client.

TLS 1.2 is the most secure version of SSL/TLS protocols. It is easy to force the connection to use it. All you need to do is to set Smtp.SSLConfiguration.EnabledSslProtocols property to SslProtocols.Tls12:

// C#

using (Smtp smtp = new Smtp())
{
    smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    smtp.ConnectSSL("smtp.example.com");

    smtp.UseBestLogin("user","password");

    // ... 

    smtp.Close();
}
' VB.NET

Using smtp As New Smtp()
	smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	smtp.ConnectSSL("smtp.example.com")

	smtp.UseBestLogin("user@example.com", "password")

	'...

	smtp.Close()
End Using

For explicit SSL/TLS, code is almost the same. You first connect to non-secure port and secure the connection using Smtp.StartTLS command:

// C#

using (Smtp smtp= new Smtp())
{
    smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    smtp.Connect("smtp.example.com");
    smtp.StartTLS();

    smtp.UseBestLogin("user@example.com","password");

    // ... 
    
    smtp.Close();
}
' VB.NET

Using smtp As New Smtp()
	smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	smtp.Connect("smtp.example.com")
	smtp.StartTLS()

	smtp.UseBestLogin("user@example.com", "password")

	'...

	smtp.Close()
End Using

To use TLS 1.2 at least .NET Framework 4.5+ must be installed on your machine and you application should target .NET 4.5+.

It is possible to use TLS 1.2 in applications targeting earlier .NET framework versions, but 4.5 must be installed on the machine. After you have .NET 4.5 installed, your 2.0-4.0 apps will use the 4.5 System.dll and you can enable TLS 1.2 using this code:

// C#

imap.SSLConfiguration.EnabledSslProtocols = (SecurityProtocolType)3072;

Using TLS 1.2 with POP3

Tuesday, July 2nd, 2019

By default most systems allow SSL 3.0, TLS 1.0, 1.2 and 1.2 to be used, when connecting using POP3 client.

TLS 1.2 is the most secure version of SSL/TLS protocols. It is easy to force the connection to use it. All you need to do is to set Pop3.SSLConfiguration.EnabledSslProtocols property to SslProtocols.Tls12:

// C#

using (Pop3 pop3 = new Pop3())
{
    pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    pop3.ConnectSSL("pop.example.com");

    pop3.UseBestLogin("user","password");

    // ... 

    pop3.Close();
}
' VB.NET

Using pop3As New Pop3()
	pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	pop3.ConnectSSL("pop.example.com")

	pop3.UseBestLogin("user@example.com", "password")

	'...

	pop3.Close()
End Using

For explicit SSL/TLS, code is almost the same. You first connect to non-secure port and secure the connection using Pop3.StartTLS command:

// C#

using (Pop3 pop3 = new Pop3())
{
    pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    pop3.Connect("pop.example.com");
    pop3.StartTLS();

    pop3.UseBestLogin("user@example.com","password");

    // ... 
    
    pop3.Close();
}
' VB.NET

Using pop3 As New Pop3()
	pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	pop3.Connect("pop.example.com")
	pop3.StartTLS()

	pop3.UseBestLogin("user@example.com", "password")

	'...

	pop3.Close()
End Using

To use TLS 1.2 at least .NET Framework 4.5+ must be installed on your machine and you application should target .NET 4.5+.

It is possible to use TLS 1.2 in applications targeting earlier .NET framework versions, but 4.5 must be installed on the machine. After you have .NET 4.5 installed, your 2.0-4.0 apps will use the 4.5 System.dll and you can enable TLS 1.2 using this code:

// C#

pop3.SSLConfiguration.EnabledSslProtocols = (SecurityProtocolType)3072;

System.Security.Authentication.AuthenticationException

Friday, December 2nd, 2016

.NET uses SChannel.dll as underlying SSL/TLS implementation. SChannel is OS dependent and if incorrectly configured or configured to use only the latest TLS/SSL versions, may lead to problems with TLS/SSL negotiation.

Please note that protocols that were considered secure some time ago, like SSL 3.0, are no longer considered secure. New OS updates may disable some protocols or cipher versions. On Windows this is done via registry settings.

SSL version status

  • SSL 2.0 was deprecated (prohibited) in 2011 by RFC 6176.
  • SSL 3.0 was deprecated by RFC 7568 in June 2015.
    As of 2014 the 3.0 version of SSL is considered insecure as it is vulnerable to the POODLE attack that affects all block ciphers in SSL; and RC4, the only non-block cipher supported by SSL 3.0, is also feasibly broken as used in SSL 3.0.
  • The use of RC4 in TLS is prohibited by RFC 7465 published in February 2015.
  • The token supplied to the function is invalid

    Full exception looks like this:

    System.Security.Authentication.AuthenticationException :
    A call to SSPI failed, see inner exception.
    ----> System.ComponentModel.Win32Exception :
    The token supplied to the function is invalid

    Most likely your client tries to use TLS 1.2 but you are using old certificate on the server (e.g. signed using md5RSA algorithm).

    There are 2 options for you:

    1. Regenerate the certificate (especially if it’s self-signed).
    2. Use older TLS/SSL version (TLS 1.1, TLS 1.0, SSL 3.0). You can force Mail.dll or Ftp.dll to use it using following code:

      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls11;
          //client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls; // TLS 1.0
          //client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Ssl3;
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      
      

      Please contact your server administrator as TLS 1.1, TLS 1.0 and SSL 3.0 aren’t considered secure anymore.

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

    Full exception looks like this:

    System.Security.Authentication.AuthenticationException :
    A call to SSPI failed, see inner exception.
    ----> System.ComponentModel.Win32Exception :
    The client and server cannot communicate, because they do not possess a common algorithm

    There are 2 possible scenarios:

    1. In most cases this means that the client is trying to use older SSL protocols like SSL 3.0, TLS 1.0 or TLS 1.1, but the remote server requires modern protocol – TLS 1.2.

      By default all our clients support TLS 1.2. Some older versions need to be told to use TLS 1.2, it is also a good practice to force TLS 1.2 only:

      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      
    2. Second option is the server is not supporting TLS 1.2 – you’ll need to use older protocol (TLS 1.1, TLS 1.0, SSL 3.0):
      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls11;
          // client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls; // TLS 1.0
          // client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Ssl3; 
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      

      Please contact your server administrator as TLS 1.1, TLS 1.0 and SSL 3.0 aren’t considered secure anymore.

    The message received was unexpected or badly formatted

    Full exception looks like this:

    System.Security.Authentication.AuthenticationException :
    A call to SSPI failed, see inner exception.
    ----> System.ComponentModel.Win32Exception :
    The message received was unexpected or badly formatted

    This error generally means that something is incorrectly configured on your machine.

    What you should try:

    1. Try forcing the latest TLS version (TLS 1.2):
      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      
    2. Use older TLS/SSL version (TLS 1.1, TLS 1.0, SSL 3.0). You can force Mail.dll or Ftp.dll to use it using following code:

      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls11;
          //client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls; // TLS 1.0
          //client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Ssl3;
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      
      

      Please contact your server administrator as TLS 1.1, TLS 1.0 and SSL 3.0 aren’t considered secure anymore.

    3. Finally you can download IISCrypto and review “Schannel” and “Cipher Suites” tabs.

      For example we have seen clients that have TLS 1.0 turned on, but have TLS_RSA_WITH_3DES_EDE_CBC_SHA cypher suite turned off. If server requires this cypher, you’ll get this error message.

      Selecting “Best Practices” and restarting, should solve the issue. You may need to select additional protocol suites depending on what your server requires

      Please note that using TLS 1.2 and forcing your server administrator to enable TLS 1.2 is the only correct and secure way to go.

    One or more of the parameters passed to the function was invalid

    Full exception looks like this:

    System.Security.Authentication.AuthenticationException:
    A call to SSPI failed, see inner exception.
    ----> System.ComponentModel.Win32Exception:
    One or more of the parameters passed to the function was invalid

    This error generally means that you are trying to use TLS/SSL protocol version that is not supported on your machine (most likely it was turned off, because it is no longer considered secure)

    What you should try:

    1. Try forcing the latest TLS version (TLS 1.2):
      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      
    2. Use older TLS/SSL version (TLS 1.1, TLS 1.0, SSL 3.0). You can force Mail.dll or Ftp.dll to use it using following code:

      using (XXX client = new XXX())
      {
          client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls11;
          //client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls; // TLS 1.0
          //client.SSLConfiguration.EnabledSslProtocols = SslProtocols.Ssl3;
      
          client.ConnectSSL("host");
      
          client.Close();
      }
      
    3. Try to disable strong crypto using code:

            const string DisableCachingName = @"TestSwitch.LocalAppContext.DisableCaching";
            const string DontEnableSchUseStrongCryptoName = @"Switch.System.Net.DontEnableSchUseStrongCrypto";
            AppContext.SetSwitch(DisableCachingName, true);
            AppContext.SetSwitch(DontEnableSchUseStrongCryptoName, true);
      

      -or- by using app.config file:

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

      ref: https://msdn.microsoft.com/en-us/library/mt298998(v=vs.110).aspx

    4. Finally you can download IISCrypto and review “Schannel” and “Cipher Suites” tabs.

      Selecting “Best Practices” restarting, should solve the issue. You may need to select additional protocol suites depending on what your server requires

      Please note that using TLS 1.2 and forcing your server administrator to enable TLS 1.2 is the only correct and secure way to go.

      Please contact your server administrator as TLS 1.1, TLS 1.0 and SSL 3.0 aren’t considered secure anymore.

    Using TLS 1.2 with IMAP

    Friday, November 18th, 2016

    By default most systems allow SSL 3.0, TLS 1.0, 1.2 and 1.2 to be used, when connecting using IMAP client.

    TLS 1.2 is the most secure version of SSL/TLS protocols. It is easy to force the connection to use it. All you need to do is to set Imap.SSLConfiguration.EnabledSslProtocols property to SslProtocols.Tls12:

    // C#
    
    using (Imap imap = new Imap())
    {
        imap.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;
    
        imap.ConnectSSL("imap.example.com");
    
        imap.UseBestLogin("user","password");
    
        // ... 
    
        imap.Close();
    }
    
    ' VB.NET
    
    Using imap As New Imap()
    	imap.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12
    
    	imap.ConnectSSL("imap.example.com")
    
    	imap.UseBestLogin("user@example.com", "password")
    
    	'...
    
    	imap.Close()
    End Using
    

    For explicit SSL/TLS, code is almost the same. You first connect to non-secure port and secure the connection using Imap.StartTLS command:

    // C#
    
    using (Imap imap= new Imap())
    {
        imap.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;
    
        imap.Connect("imap.example.com");
        imap.StartTLS();
    
        imap.UseBestLogin("user@example.com","password");
    
        // ... 
        
        imap.Close();
    }
    
    ' VB.NET
    
    Using imap As New Imap()
    	imap.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12
    
    	imap.Connect("imap.example.com")
    	imap.StartTLS()
    
    	imap.UseBestLogin("user@example.com", "password")
    
    	'...
    
    	imap.Close()
    End Using
    

    To use TLS 1.2 at least .NET Framework 4.5+ must be installed on your machine and you application should target .NET 4.5+.

    It is possible to use TLS 1.2 in applications targeting earlier .NET framework versions, but 4.5 must be installed on the machine. After you have .NET 4.5 installed, your 2.0-4.0 apps will use the 4.5 System.dll and you can enable TLS 1.2 using this code:

    // C#
    
    imap.SSLConfiguration.EnabledSslProtocols = (SecurityProtocolType)3072;
    

    SSL vs TLS vs STARTTLS

    Wednesday, October 9th, 2013

    There’s often quite a confusion about the different terms: SSL, TLS, STARTTLS and STLS.

    SSL and TLS

    SSL and TLS are cryptographic protocols, both provide a way to encrypt communication channel between two machines over the Internet (e.g. client computer and a server). SSL stands for Secure Sockets Layer and current version is 3.0. TLS stands for Transport Layer Security and the current version is 1.2. TLS is the successor to SSL. The terms SSL and TLS can be used interchangeably, unless you’re referring to a specific protocol version.

    Version numbering is inconsistent between SSL and TLSs. When TLS took over SSL as the preferred protocol name, it began with a new version number. The ordering of protocols in terms of oldest to newest is: SSLv2, SSLv3, TLSv1.0, TLSv1.1, TLSv1.2.

    STARTTLS and STLS

    STARTTLS is a protocol command, that is issued by an email client. It indicates, that the client wants to upgrade existing, insecure connection to a secure connection using SSL/TLS cryptographic protocol. STARTTLS command name is used by SMTP and IMAP protocols, whereas POP3 protocol uses STLS as the command name.

    Despite having TLS in the name, STARTTLS doesn’t mean TLS will be used. Both SSL and TLS are acceptable protocols for securing the communication.

    Clear text/Plain text

    No security protocol is used at all. All commands, responses and data are transferred in plain text.

    client.Connect("mail.example.com");
    

    Implict SSL mode

    Implict SSL mode means, that you connect to SSL/TLS encrypted port.

    client.ConnectSSL("mail.example.com");
    

    Explicit SSL mode

    Explicit SSL mode means, that you connect to plaint text port and secure the connection by issuing STARTTLS (or STLS) command afterwards (you explicitly secure the connection).

    client.Connect("mail.example.com");
    client.StartTLS();
    

    Securing the connection

    Regardless of whether you use implict (connecting to an SSL/TLS encrypted port) or explicit (using STARTTLS to upgrade an existing connection) mode, both sides will negotiate which protocol and which version to use. This negotiation is based on how client and server have been configured and what each side supports.

    SSL/TLS support

    Support for SSL/TLS is virtually universal, however which versions are supported is variable. Pretty much everything supports SSLv3. Most machines support TLSv1.0.

    TLS vs STARTTLS naming problem

    One significant complicating factor is that some email software incorrectly uses the term TLS when they should have used “STARTTLS” or “explicit SSL/TLS”. Older versions of Thunderbird used “TLS” to mean “enforce use of STARTTLS to upgrade the connection, and fail if STARTTLS is not supported” and “TLS, if available” to mean “use STARTTLS to upgrade the connection, if the server advertises support for it, otherwise just use an insecure connection” (very problematic, as we’ll see below).

    Port numbers

    To add security to some existing protocols (IMAP, POP3, SMTP), it was decided to just add SSL/TLS encryption as a layer underneath the existing protocol. However to distinguish that software should talk the SSL/TLS encrypted version of the protocol rather than the plaintext one, a different port number was used for each protocol:

    Protocol Plain text SSL
    IMAP 143 993
    POP3 110 995
    SMTP 587 or 25 465

    Too many ports? Solution: Plain text + STARTTLS

    At some point, it was decided that having 2 ports for every protocol was wasteful, and instead it’s better to have 1 port, that starts off as plain text, but clients can upgrade the connection to an SSL/TLS encrypted one using STARTTLS (or STLS for POP3 protocol) command.

    STARTTLS problems

    There were a few problems with this. There exists lots of software, that used the alternate port numbers with pure SSL/TLS connections. Client software can be very long lived, so you can’t just disable the encrypted ports until all software has been upgraded.

    Each protocol received mechanisms to tell clients that the server supported upgrading to SSL/TLS (e.g. STARTTLS in IMAP’s CAPABILITY response), and that they should not attempt to login without doing the STARTTLS upgrade (LOGINDISABLED in IMAP’s CAPABILITY response). This created two unfortunate situations:

    • Some software just ignored the “login disabled until upgraded” announcement (LOGINDISABLED, STARTTLS) and just tried to log in anyway, sending the user login name and password over clear text channel. The server rejected the login and password, but the details had already been sent over the Internet in plain text.
    • Other software saw the “login disabled until upgraded” announcement, but then wouldn’t upgrade the connection automatically, and thus reported login errors back to the user, which caused confusion about what was wrong.
      • Both of these problems resulted in significant compatibility issues with existing clients, and so most system administrators continued to just use plain text connections on one port, and encrypted connections on a separate port number.

        Disable plain text for IMAP and POP3

        Many companies (e.g. Gmail, Outlook.com) disabled plain IMAP (port 143) and plain POP3 (port 110), so people must use a SSL/TLS encrypted connection – this removes the need for having STARTTLS command completely.

        SMTP STARTTLS stays

        The one real exception to the above is SMTP. Most email software used SMTP on port 25 to submit messages to the email server for onward transmission to the destination. However SMTP was originally designed for transfer, not submission. So yet another port (587) was defined for message submission.

        Port 587 doesn’t mandate requiring STARTTLS, however the use of port 587 became popular around the same time as the realization that SSL/TLS encryption of communications between clients and servers was an important issue. The result is that most systems, that offer message submission over port 587 require clients to use STARTLS to upgrade the connection. Login and password to authenticate is also required.

        There has been an additional benefit to this approach as well. By moving users away from using port 25 for email submission, ISPs can block outgoing port 25 connections from users’ computers, which were a significant source of spam, due to user computers infected with spam sending viruses.

        Further readings

        Using SSL/TLS with IMAP
        Using SSL/TLS with SMTP
        Using SSL/TLS with POP3