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ivan  
#1 Posted : Monday, May 2, 2011 5:18:16 PM(UTC)
ivan

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VB6 Example

Digital signature is always signed by sender certificate. The certificate used to sign email content MUST have the public/private key pair. First of all, the user MUST get a digital certificate for personal email protection from third-party certificate authorities such as www.verisign.com. After the certificate is installed on the machine, it can be viewed by "Control Panel"->"Internet Options"->"Content"->"Certificates"->"Personal". When you view the certificate, please note there is a line "You have a private key that corresponds to this certificate" in the certificate view, that means you are able to use this certificate to sign email content. If this line doesn't appear, that means you are unable to sign the email content by this certificate. To sign email content, please refer to EASendMail SMTP Component.

How to encrypt email?

Encrypting email doesn't require sender certificate but the certificate with public key for every recipient. For example, from@adminsystem.com sends an email to rcpt@adminsystem.com with digital signature. The digital signature contains the public key certificate for from@adminsystem.com, then rcpt@adminsystem.com can send an encrypted email with this certificate back to from@adminsystem.com. Only from@adminsystem can read this email, because this email MUST be decrypted by private key of from@adminsystem.com. Therefore, you MUST receive an digital signed email from other people (Most email clients such as outlook, outlook express will add the certificate to the Other People Storage automatically once an digital signed email is received) before you can send encrypted email to this people. To encrypt email, please refer to EASendMail SMTP Component.

EAGetMail Mail class provides an easy way to verify the email digital signature and get the signer certificate. The signer certificate only contains the public key, that means you can add this certificate to your user certificate storage so that you can use this certificate to encrypt email and send the encrypted email back to the sender, only the sender can decrypt the email.

The following code demonstrates how to verify S/MIME digital signature and decrypt encrypted email.
Code:

' The following example codes demonstrate parsing S/MIME email - digital signature and decryption
' To get full sample projects, please download and install EAGetMail on your machine.
' To run it correctly, please change email server, user, password, folder, file name value to yours

Option Explicit 

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 ParseEmail(ByVal emlFile As String) 
    Dim oMail As New EAGetMailObjLib.Mail 
    oMail.LicenseCode = "TryIt" 

On Error GoTo ErrorHandle 
    oMail.LoadFile emlFile, False 

     If oMail.IsEncrypted Then 
        ' This email is encrypted, we decrypt it by user default certificate.
        ' You can also use specified certificate like this
        ' Dim oCert As New EAGetMailObjLib.Certificate
        ' oCert.LoadFromFile "c:\test.pfx", "pfxpassword", CRYPT_USER_KEYSET
        ' Set oMail = oMail.Decrypt(oCert)
        Set oMail = oMail.Decrypt(Nothing) 
    End If 

    If oMail.IsSigned Then 
        ' This email is digital signed.
        Dim oCert As EAGetMailObjLib.Certificate 
        Set oCert = oMail.VerifySignature 
        MsgBox "This email contains a valid digital signature." 
        ' You can add the certificate to your certificate storage like this
        ' oCert.AddToStore CERT_SYSTEM_STORE_CURRENT_USER, "addressbook"
        ' Then you can use send the encrypted email back to this sender.
    End If 

    ' Parse email sender
    MsgBox "From: " & oMail.From.Address 

    Dim arAddr 
    Dim i As Integer 
    Dim addr As EAGetMailObjLib.MailAddress 

    ' Parse email to recipients
    arAddr = oMail.To 
    For i = LBound(arAddr) To UBound(arAddr) 
        Set addr = arAddr(i) 
        MsgBox "To: " & addr.Address 
    Next 

    ' Parse email cc
    arAddr = oMail.Cc 
    For i = LBound(arAddr) To UBound(arAddr) 
        Set addr = arAddr(i) 
        MsgBox "Cc: " & addr.Address 
    Next 

    ' Parse email subject
    MsgBox "Subject: " & oMail.Subject 

    ' Parse email text body
    MsgBox "Text body: " & oMail.TextBody 

    ' Parse email HTML body
    MsgBox "Html body: " & oMail.HtmlBody 

    Dim atts 
    Dim att As EAGetMailObjLib.Attachment 

    ' Parse attachments
    atts = oMail.Attachments 
    For i = LBound(atts) To UBound(atts) 
        Set att = atts(i) 
        MsgBox "Attachment: " & att.name 
    Next 

    Exit Sub 
ErrorHandle: 
    MsgBox Err.Description 
End Sub 

Private Sub Command1_Click() 

    ParseEmail "c:\my folder\test.eml" 

    Exit Sub 
ErrorHandle: 
    MsgBox Err.Description 
End Sub 


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