Encrypt Email in VB 6.0 - S/MIME with RC2, 3DES and RSAES-OAEP

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.


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.


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.


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


Const ConnectNormal = 0
Const ConnectSSLAuto = 1
Const ConnectSTARTTLS = 2
Const ConnectDirectSSL = 3
Const ConnectTryTLS = 4

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"

    ' Add digital signature
    If Not oSmtp.SignerCert.FindSubject("test@emailarchitect.net", _
        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

    ' 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"

    ' ConnectTryTLS means if server supports SSL/TLS connection, SSL/TLS is used automatically
    oSmtp.ConnectType = ConnectTryTLS

    ' If your server uses 587 port
    ' oSmtp.ServerPort = 587

    ' If your server uses 25/587/465 port with SSL/TLS
    ' oSmtp.ConnectType = ConnectSSLAuto
    ' oSmtp.ServerPort = 25 ' 25 or 587 or 465

    MsgBox "start to send email ..."
    If oSmtp.SendMail() = 0 Then
        MsgBox "email was sent successfully!"
        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

Encryption Algorithm

You can use EncryptionAlgorithm property to set RC2, RC4, 3DES, AES128, AES192 or AES256 encryption algorithm. RSAES-OAEP (AES128, AES192 and AES256) is recommended.

RSA-OAEP Encryption with SHA256 HASH

If you need to use RSA-OAEP encryption with sha256 scheme based on EDIFACT rule, please have a look at this topic:

RSASSA-PSS + RSA-OAEP Encryption with SHA256

Next Section

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



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