Encrypt Email in VB 6.0 - S/MIME

In previous section, I introduced how to send email with digital signature. In this section, I will introduce how to encrypt email with digital certificate in VB 6.0.

Introduction

After the recipient received your email with digital signature, the recipient can get your digital certificate public key from your digital signature. Then the recipient can encrypt an email with your public key and send it to you. Only you can decrypt this email with your private key. That is how S/MIME can protect your email content. If you don’t expose your digital certificate private key to others, none can read your email which is encrypted by your public key.

If you received an email with digital signature, your email client usually stores the public key of the sender in “Control Panel” -> “Internet Options” -> “Content” -> “Certificates” -> “Other People”.

Then you can use the following code to encrypt email and send it to your recipient.

Note

Remarks: All of samples in this section are based on first section: Send email in a simple VB 6.0 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.

[VB 6.0 - Email Encryption (S/MIME) - Example]

The following example codes demonstrate how to encrypt email with digital certificate in VB6.

Note

To get the full sample projects, please refer to Samples section.

Const CRYPT_MACHINE_KEYSET = 32
Const CRYPT_USER_KEYSET = 4096
Const CERT_SYSTEM_STORE_CURRENT_USER = 65536
Const CERT_SYSTEM_STORE_LOCAL_MACHINE = 131072
Private Sub Command1_Click()

    Dim oSmtp As New EASendMailObjLib.Mail
    oSmtp.LicenseCode = "TryIt"

    ' Set your sender email address
    oSmtp.FromAddr = "test@emailarchitect.net"

    ' Add recipient email address
    oSmtp.AddRecipientEx "support@emailarchitect.net", 0

    ' Set email subject
    oSmtp.Subject = "test encrypted email from VB 6.0 project"

    ' Set email body
    oSmtp.BodyText = "this is a test encrypted email sent from VB 6.0 project"

    ' Your SMTP server address
    oSmtp.ServerAddr = "smtp.emailarchitect.net"

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

    ' If your smtp server requires SSL connection, please add this line
    ' oSmtp.SSL_init

    ' Add digital signature
    If Not oSmtp.SignerCert.FindSubject("test@emailarchitect.net", _
        CERT_SYSTEM_STORE_CURRENT_USER, "my") Then
        MsgBox oSmtp.SignerCert.GetLastError()
        Exit Sub
    End If

    If Not oSmtp.SignerCert.HasPrivateKey Then
        MsgBox "Signer certificate has not private key, " & _
             " this certificate can not be used to sign email!"
        Exit Sub
    End If

    ' Find the encrypting certificate for every recipients
    Dim oEncryptCert As New EASendMailObjLib.Certificate
    If Not oEncryptCert.FindSubject("support@emailarchitect.net", _
                            CERT_SYSTEM_STORE_CURRENT_USER, "AddressBook") Then
        If Not oEncryptCert.FindSubject("support@emailarchitect.net", _
                                        CERT_SYSTEM_STORE_CURRENT_USER, "my") Then
            MsgBox oEncryptCert.GetLastError()
            Exit Sub
        End If
    End If

    ' Add encrypting certificate
    oSmtp.RecipientsCerts.Add oEncryptCert

    MsgBox "start to send email ..."
    If oSmtp.SendMail() = 0 Then
        MsgBox "email was sent successfully!"
    Else
        MsgBox "failed to send email with the following error:" & oSmtp.GetLastErrDescription()
    End If

End Sub

If you received digital signed and encrypted email by Windows Mail(Outlook Express), it looks like this:

VB 6.0 sign and encrypt email - s/mime

Next Section

At next section I will introduce how to send email with event handler in asynchronous mode.

Appendix

Comments

If you have any comments or questions about above example codes, please click here to add your comments.