MIME¶

The following C# example codes demonstrate how to sign email to S/MIME format with digital signature (RSASSA-PSS + SHA256) and how to encrypt email with RSAES-OAEP + AES 128/192/256 + SHA256.

Sections:

EDIFACT rule in EUROPE
EASendMail with Bouncy Castle
C# - Sign email with RSASSA-PSS + SHA256 - EDIFACT - S/MIME - example
C# - Encrypt email with RRSAES-OAEP + AES 128/192/256 + SHA256 - EDIFACT - S/MIME - example
C# - Sign email with RSASSA-PSS + SHA256 and encrypt email with RRSAES-OAEP + AES 128/192/256 + SHA256 - EDIFACT - S/MIME - example
TLS 1.2 protocol

EDIFACT rule in EUROPE¶

Latest EDIFACT requires RSA-SHA256 Signature Algorithm + RSASSA-PSS with SHA256 padding for digital signature, and AES128/192/256 Encrypting Algorithm + RSAES-OAEP + SHA256 Hash for email encryption.

EASendMail uses Windows/.NET built-in function to implement S/MIME, it supports RSASSA-PSS signature + SHA1 padding and AES + RSAES-OAEP, however it has a compatible problem with RSASSA-PSS signature defined in latest EDIFACT (SHA256 padding).

To comply with EDIFACT rule, we implemented a special version with Bouncy Castle library.

EASendMail with Bouncy Castle¶

If you need to sign email with digital signature or encrypt email based on the rule of EDIFACT in EUROPE, you should use this version:

You can download it from: http://www.emailarchitect.net/webapp/download/easendmail.bc.exe

To use it in your project, the first step is Add reference of EASendMail BC to your project. Please create or open your project with Visual Studio, then go to menu -> Project -> Add Reference -> .NET -> Browse..., and select Installation Path\Lib\net[version]\EASendMail.dll from your disk, click Open -> OK.

The default Installation path is C:\Program Files (x86)\EASendMail.BC\

You can also install the run-time assembly by NuGet. Run the following command in the NuGet Package Manager Console:

Install-Package EASendMail.BC

C# - Sign email with RSASSA-PSS + SHA256 - EDIFACT - S/MIME - example¶

The following example codes demonstrate signing email based on EDIFACT rule - S/MIME. In order to run it correctly, please change SMTP server, user, password, sender, recipient value to yours.

using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography.X509Certificates;

// Add EASendMail namespace
using EASendMail;

namespace mysendemail
{
    class Program
    {
        static X509Certificate2 _findCertificate(string storeName, string emailAddress)
        {
            X509Certificate2 cert = null;

            X509Store store = new X509Store(storeName, StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly);

            X509Certificate2Collection certfiicates = store.Certificates.Find(X509FindType.FindBySubjectName, emailAddress, true);
            if (certfiicates.Count > 0)
            {
                cert = certfiicates[0];
            }

            store.Close();

            return cert;
        }

        static void Main(string[] args)
        {
            try
            {
                SmtpMail oMail = new SmtpMail("TryIt");

                // Set sender email address, please change it to yours
                oMail.From = "test@emailarchitect.net";

                // Set recipient email address, please change it to yours
                oMail.To = "support@emailarchitect.net";

                // Set email subject
                oMail.Subject = "test email with digital signature from c#";

                // Set email body
                oMail.TextBody = "this is a test email with digital signature based on EDIFACT rule";

                // Digital signature with sha256 hash algorithm + RSASSA-PSS signature + sha256 padding
                oMail.SignatureHashAlgorithm = SignatureHashAlgorithmType.SHA256;
                oMail.SignatureHashEncryption = SignatureHashEncryptionType.RSA_SSA_PSS_WITH_PARAMETER;

                X509Certificate2 signerCertificate = _findCertificate("My", oMail.From.Address);
                if (signerCertificate == null)
                    throw new Exception("No signer certificate found for " + oMail.From.Address + "!");

                oMail.From.Certificate2 = signerCertificate;

                // You can also load the signer certificate from a pfx file.
                /* string pfxPath = "D:\\TestCerts\\signer.pfx";
                X509Certificate2 signerCertFromPfx = new X509Certificate2(pfxPath,
                    "nosecret",
                    X509KeyStorageFlags.Exportable | X509KeyStorageFlags.UserKeySet);

                oMail.From.Certificate2 = signerCertFromPfx;
                */
                // If you use it in web application,
                // please use  X509KeyStorageFlags.Exportable | X509KeyStorageFlags.MachineKeySet

                // If you use it in .NET core application
                // please use X509KeyStorageFlags.Exportable | X509KeyStorageFlags.EphemeralKeySet

                // Your smtp server address
                SmtpServer oServer = new SmtpServer("smtp.emailarchitect.net");

                // User and password for ESMTP authentication, if your server doesn't require
                // User authentication, please remove the following codes.
                oServer.User = "test@emailarchitect.net";
                oServer.Password = "testpassword";

                // Most mordern SMTP servers require SSL/TLS connection now.
                // ConnectTryTLS means if server supports SSL/TLS, SSL/TLS will be used automatically.
                oServer.ConnectType = SmtpConnectType.ConnectTryTLS;

                // If your SMTP server uses 587 port
                // oServer.Port = 587;

                // If your SMTP server requires SSL/TLS connection on 25/587/465 port
                // oServer.Port = 25; // 25 or 587 or 465
                // oServer.ConnectType = SmtpConnectType.ConnectSSLAuto;

                Console.WriteLine("start to send email with digital signature ...");

                SmtpClient oSmtp = new SmtpClient();
                oSmtp.SendMail(oServer, oMail);

                Console.WriteLine("email was sent successfully!");
            }
            catch (Exception ep)
            {
                Console.WriteLine("failed to send email with the following error:");
                Console.WriteLine(ep.Message);
            }
        }
    }
}

Note

RSASSA-PSS signature generated by Bouncy Castle is not verified by most email clients (outlook, firebird …), but it does meet the requirement in EDIFACT rule.

C# - Encrypt email with RRSAES-OAEP + AES 128/192/256 + SHA256 - EDIFACT - S/MIME - example¶

The following example codes demonstrate encrypting email message based on EDIFACT rule - S/MIME. In order to run it correctly, please change SMTP server, user, password, sender, recipient value to yours.

using System;
using System.Collections.Generic;
using System.Text;

using System.Security.Cryptography.X509Certificates;
// Add EASendMail namespace
using EASendMail;

namespace mysendemail
{
    class Program
    {
        static X509Certificate2 _findCertificate(string storeName, string emailAddress)
        {
            X509Certificate2 cert = null;

            X509Store store = new X509Store(storeName, StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly);

            X509Certificate2Collection certfiicates = store.Certificates.Find(X509FindType.FindBySubjectName, emailAddress, true);
            if (certfiicates.Count > 0)
            {
                cert = certfiicates[0];
            }

            store.Close();

            return cert;
        }

        static void Main(string[] args)
        {
            try
            {
                SmtpMail oMail = new SmtpMail("TryIt");

                // Set sender email address, please change it to yours
                oMail.From = "test@emailarchitect.net";

                // Set recipient email address, please change it to yours
                oMail.To = "support@emailarchitect.net";

                // Set email subject
                oMail.Subject = "test encrypted email from c#";

                // Set email body
                oMail.TextBody = "this is a test email with email encryption based on EDIFACT rule";

                // Email encryption with RAES-OAEP-128 + sha-256 oaep hash algorithm
                oMail.EncryptionAlgorithm = EncryptionAlgorithmType.RAES_OAEP_128;
                // RAES_OAEP_128 uses AES128, you can also use  RAES_OAEP_192 (AES192) and RAES_OAEP_256 (AES256)
                oMail.OaepHashAlgorithm = OaepHashAlgorithmType.SHA256;

                int count = oMail.To.Count;
                for (int i = 0; i < count; i++)
                {
                    MailAddress oAddress = oMail.To[i] as MailAddress;
                    X509Certificate2 encryptCert = _findCertificate("AddressBook", oAddress.Address);
                    if (encryptCert == null)
                        encryptCert = _findCertificate("My", oAddress.Address);

                    if (encryptCert == null)
                        throw new Exception("No encryption certificate found for " + oAddress.Address + "!");

                    oAddress.Certificate2 = encryptCert;

                    // You can also load the encryptor certificate from a cer file like this
                    /*
                    string cerPath = "D:\\TestCerts\\encryptor.cer";
                    X509Certificate2 encryptCertFromFile = new X509Certificate2(cerPath);
                    oAddress.Certificate2 = encryptCertFromFile;
                    */
                }

                // Your SMTP server address
                SmtpServer oServer = new SmtpServer("smtp.emailarchitect.net");

                //User and password for ESMTP authentication, if your server doesn't require
                //User authentication, please remove the following codes.
                oServer.User = "test@emailarchitect.net";
                oServer.Password = "testpassword";

                // Most mordern SMTP servers require SSL/TLS connection now.
                // ConnectTryTLS means if server supports SSL/TLS, SSL/TLS will be used automatically.
                oServer.ConnectType = SmtpConnectType.ConnectTryTLS;

                // If your SMTP server uses 587 port
                // oServer.Port = 587;

                // If your SMTP server requires SSL/TLS connection on 25/587/465 port
                // oServer.Port = 25; // 25 or 587 or 465
                // oServer.ConnectType = SmtpConnectType.ConnectSSLAuto;

                Console.WriteLine("start to send encrypted email ...");

                SmtpClient oSmtp = new SmtpClient();
                oSmtp.SendMail(oServer, oMail);

                Console.WriteLine("email was sent successfully!");
            }
            catch (Exception ep)
            {
                Console.WriteLine("failed to send email with the following error:");
                Console.WriteLine(ep.Message);
            }
        }
    }
}

C# - Sign email with RSASSA-PSS + SHA256 and encrypt email with RRSAES-OAEP + AES 128/192/256 + SHA256 - EDIFACT - S/MIME - example¶

The following example codes demonstrate signing and encrypting email message based on EDIFACT rule - S/MIME. In order to run it correctly, please change SMTP server, user, password, sender, recipient value to yours.

using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography.X509Certificates;

// Add EASendMail namespace
using EASendMail;

namespace mysendemail
{
    class Program
    {
        static X509Certificate2 _findCertificate(string storeName, string emailAddress)
        {
            X509Certificate2 cert = null;

            X509Store store = new X509Store(storeName, StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly);

            X509Certificate2Collection certfiicates = store.Certificates.Find(X509FindType.FindBySubjectName, emailAddress, true);
            if (certfiicates.Count > 0)
            {
                cert = certfiicates[0];
            }

            store.Close();

            return cert;
        }

        static void Main(string[] args)
        {
            try
            {
                SmtpMail oMail = new SmtpMail("TryIt");

                // Set sender email address, please change it to yours
                oMail.From = "test@emailarchitect.net";

                // Set recipient email address, please change it to yours
                oMail.To = "support@emailarchitect.net";

                // Set email subject
                oMail.Subject = "test signed and encrypted email from c#";

                // Set email body
                oMail.TextBody = "this is a test signed and encrypted based on EDIFACT rule";

                // Digital signature with sha256 hash algorithm + RSASSA-PSS signature + sha256 padding
                oMail.SignatureHashAlgorithm = SignatureHashAlgorithmType.SHA256;
                oMail.SignatureHashEncryption = SignatureHashEncryptionType.RSA_SSA_PSS_WITH_PARAMETER;

                X509Certificate2 signerCertificate = _findCertificate("My", oMail.From.Address);
                if (signerCertificate == null)
                    throw new Exception("No signer certificate found for " + oMail.From.Address + "!");

                oMail.From.Certificate2 = signerCertificate;

                // You can also load the signer certificate from a pfx file.
                /* string pfxPath = "D:\\TestCerts\\signer.pfx";
                X509Certificate2 signerCertFromPfx = new X509Certificate2(pfxPath,
                    "nosecret",
                    X509KeyStorageFlags.Exportable | X509KeyStorageFlags.UserKeySet);

                oMail.From.Certificate2 = signerCertFromPfx;
                */
                // If you use it in web application,
                // please use  X509KeyStorageFlags.Exportable | X509KeyStorageFlags.MachineKeySet

                // If you use it in .NET core application
                // please use X509KeyStorageFlags.Exportable | X509KeyStorageFlags.EphemeralKeySet

                // Email encryption with RAES-OAEP-128 + sha-256 oaep hash algorithm
                oMail.EncryptionAlgorithm = EncryptionAlgorithmType.RAES_OAEP_128;
                // RAES_OAEP_128 uses AES128, you can also use  RAES_OAEP_192 (AES192) and RAES_OAEP_256 (AES256)
                oMail.OaepHashAlgorithm = OaepHashAlgorithmType.SHA256;

                int count = oMail.To.Count;
                for (int i = 0; i < count; i++)
                {
                    MailAddress oAddress = oMail.To[i] as MailAddress;
                    X509Certificate2 encryptCert = _findCertificate("AddressBook", oAddress.Address);
                    if (encryptCert == null)
                        encryptCert = _findCertificate("My", oAddress.Address);

                    if (encryptCert == null)
                        throw new Exception("No encryption certificate found for " + oAddress.Address + "!");

                    oAddress.Certificate2 = encryptCert;

                    // You can also load the encryptor certificate from a cer file like this
                    /*
                    string cerPath = "D:\\TestCerts\\encryptor.cer";
                    X509Certificate2 encryptCertFromFile = new X509Certificate2(cerPath);
                    oAddress.Certificate2 = encryptCertFromFile;
                    */
                }

                // Your SMTP server address
                SmtpServer oServer = new SmtpServer("smtp.emailarchitect.net");

                //User and password for ESMTP authentication, if your server doesn't require
                //User authentication, please remove the following codes.
                oServer.User = "test@emailarchitect.net";
                oServer.Password = "testpassword";

                // Most mordern SMTP servers require SSL/TLS connection now.
                // ConnectTryTLS means if server supports SSL/TLS, SSL/TLS will be used automatically.
                oServer.ConnectType = SmtpConnectType.ConnectTryTLS;

                // If your SMTP server uses 587 port
                // oServer.Port = 587;

                // If your SMTP server requires SSL/TLS connection on 25/587/465 port
                // oServer.Port = 25; // 25 or 587 or 465
                // oServer.ConnectType = SmtpConnectType.ConnectSSLAuto;

                Console.WriteLine("start to send encrypted email ...");

                SmtpClient oSmtp = new SmtpClient();
                oSmtp.SendMail(oServer, oMail);

                Console.WriteLine("email was sent successfully!");
            }
            catch (Exception ep)
            {
                Console.WriteLine("failed to send email with the following error:");
                Console.WriteLine(ep.Message);
            }
        }
    }
}

TLS 1.2 protocol¶

TLS is the successor of SSL, more and more SMTP servers require TLS 1.2 encryption now.

If your operating system is Windows XP/Vista/Windows 7/Windows 2003/2008/2008 R2/2012/2012 R2, you need to enable TLS 1.2 protocol in your operating system like this:

Enable TLS 1.2 on Windows XP/Vista/7/10/Windows 2008/2008 R2/2012

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