In previous section, I introduced how to send email with embedded images. In this section, I will introduce how to send email with digital signature (S/MIME) in VB.NET.
Digital signature prevents email content is faked or changed in transport level. Encrypting email protects email content from exposure to inappropriate recipients. Both digital signature and email encrypting depend on digital certificate.
If you have an email digital signature certificate installed on your machine, you can find it in “Control Panel” -> “Internet Options” -> “Content” -> “Certificates” -> “Personal”.
Then you can use your email certificate to sign the email by the following code. If you don’t have a certificate for your email address, you MUST get a digital certificate for personal email protection from third-party certificate authorities such as www.verisign.com.
If you need a free certificate for your email address, you can go to http://www.comodo.com/home/email-security/free-email-certificate.php to apply for one year free email certificate.
Remarks: All of samples in this section are based on first section: Send email in a simple VB.NET project. To compile and run the following example codes successfully, please click here to learn how to create the test project and add reference of EASendMail to your project.
The following example codes demonstrate how to send email with digital signature in VB.NET.
To get the full sample projects, please refer to Samples section.
Imports System.Security.Cryptography.X509Certificates Imports EASendMail 'Add EASendMail namespace Module Module1 Private Function _findCertificate(storeName As String, emailAddress As String) As X509Certificate2 Dim cert As X509Certificate2 = Nothing Dim store As New X509Store(storeName, StoreLocation.CurrentUser) store.Open(OpenFlags.ReadOnly) Dim certfiicates As X509Certificate2Collection = store.Certificates.Find(X509FindType.FindBySubjectName, emailAddress, True) If certfiicates.Count > 0 Then cert = certfiicates(0) End If store.Close() _findCertificate = cert End Function Sub Main() Try Dim oMail As New SmtpMail("TryIt") ' Set sender email address, please change it to yours oMail.From = "firstname.lastname@example.org" ' Set recipient email address, please change it to yours oMail.To = "email@example.com" ' Set email subject oMail.Subject = "test email with digital signature" ' Set email body oMail.TextBody = "this is a test email with digital signature (S/MIME)" Dim signerCertificate As X509Certificate2 = _findCertificate("My", oMail.From.Address) If signerCertificate Is Nothing Then Throw New Exception("No signer certificate found for " + oMail.From.Address + "!") End If oMail.From.Certificate2 = signerCertificate ' You can also load the signer certificate from a pfx file. ' ' Dim pfxPath As String = "D:\TestCerts\signer.pfx" ' Dim signerCertFromPfx As X509Certificate2 = New X509Certificate2(pfxPath, ' "nosecret", ' X509KeyStorageFlags.Exportable Or X509KeyStorageFlags.UserKeySet) ' oMail.From.Certificate2 = signerCertFromPfx ' If you use it in web application, ' please use X509KeyStorageFlags.Exportable Or X509KeyStorageFlags.MachineKeySet ' If you use it in .NET core application ' please use X509KeyStorageFlags.Exportable Or X509KeyStorageFlags.EphemeralKeySet ' Your SMTP server address Dim oServer As New SmtpServer("smtp.emailarchitect.net") ' User and password for ESMTP authentication oServer.User = "firstname.lastname@example.org" 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 ...") Dim oSmtp As New SmtpClient() oSmtp.SendMail(oServer, oMail) Console.WriteLine("email was sent successfully!") Catch ep As Exception Console.WriteLine("failed to send email with the following error:") Console.WriteLine(ep.Message) End Try End Sub End Module
You can use SmtpMail.SignatureHashAlgorithm property to set MD5, SHA1, SHA256, SHA384 or SHA512 signature algorithm. SHA256 is recommended.
RSASSA-PSS Signature in EDIFACT
If you need to use RSASSA-PSS signature scheme based on EDIFACT rule, you need a special version of EASendMail, please have a look at this topic:
RSASSA-PSS + RSA-OAEP Encryption with SHA256
At next section I will introduce how to encrypt email with digital certificate.
If you have any comments or questions about above example codes, please click here to add your comments.