Delphi - Verify Digital Signature and Decrypt Email - S/MIME

The following delphi codes demonstrate how to verify S/MIME digital signature and decrypt encrypted email.

How to sign email?

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.

Installation

Before you can use the following sample codes, you should download the EAGetMail Installer and install it on your machine at first. Full sample projects are included in this installer.

Add Reference

To use EAGetMail ActiveX Object in your Delphi project, the first step is “Add Unit file of EAGetMail to your project”. Please go to C:\Program Files\EAGetMail\Samples_Delphi\pop3_imap4_simple.delphi or C:\Program Files (x86)\EAGetMail\Samples_Delphi\pop3_imap4_simple.delphi folder, find EAGetMailObjLib_TLB.pas, and then copy this file to your project folder.

// include EAGetMailObjLib_TLB unit to your Delphi Project
unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, EAGetMailObjLib_TLB, StdCtrls;

Then you can start to use it in your Delphi Project.

You can also create EAGetMailObjLib_TLB.pas manually by Delphi like this:

  • Delphi 7 or eariler version

    First of all, create a standard delphi project: select menu Project -> Import Type Library, checked EAGetMail ActiveX Object and click Create Unit. Then include EAGetMailObjLib_TLB in your project.

    add reference in Delphi
  • Delphi XE or later version

    First of all, create a standard delphi project: select menu Component -> Import component... -> Import a type library -> checked EAGetMail ActiveX Object, have Generate Component Wrapper checked and click “Create Unit”. Then include EAGetMailObjLib_TLB in your project.

Delphi - Verify Digital Signature and Decrypt Email - S/MIME - Example

The following example codes demonstrate parsing S/MIME email - digital signature and decryption. In order to run it correctly, please change email server, user, password, folder, file name value to yours.

Note

To get full sample projects, please download and install EAGetMail on your machine.

Unit Unit1;

Interface

Uses
    Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
    Dialogs, StdCtrls, EAGetMailObjLib_TLB;

Type
    TForm1 = Class(TForm)
        Button1: TButton;
        Procedure Button1Click(Sender: TObject);
    private
        { Private declarations }
    public
        { Public declarations }
End;

Const
    MailServerPop3 = 0;
    MailServerImap4 = 1;   CRYPT_MACHINE_KEYSET = 32;
    CRYPT_USER_KEYSET = 4096;
    CERT_SYSTEM_STORE_CURRENT_USER = 65536;
    CERT_SYSTEM_STORE_LOCAL_MACHINE = 131072;

Var
    Form1: TForm1;

Implementation

{$R *.dfm}

Procedure TForm1.ParseEmail(fileName: WideString);
Var
    oMail: TMail;
    i, UBound: Integer;
    addrs, atts: OleVariant;
    addr: IMailAddress;
    att: IAttachment;
    oCert: TCertificate;
    oSignerCert: ICertificate;
Begin
    oMail := TMail.Create(Application);
    oMail.LicenseCode := 'TryIt';
    oMail.LoadFile(fileName, false);
    ShowMessage(oMail.Headers.GetValueOfKey('Content-Type'));
    If oMail.IsEncrypted Then
    Try
        // this email is encrypted, decrypt it by default user certificate
        oMail.ConnectTo(oMail.Decrypt(nil));
        // You can also use specified certificate like this
        // oCert := TCertificate.Create(Application);
        // oCert.LoadFromFile('c:\test.pfx', 'pfxpassword', CRYPT_USER_KEYSET);
        // oMail.Load(oMail.Decrypt(oCert.DefaultInterface).Content);
    Except
        On ep: Exception Do
        Begin
            ShowMessage('Decrypt Error: ' + ep.Message);
        End;
    End;

    If oMail.IsSigned Then
    Try
        // this email is digital signed, verify signature
        oSignerCert := oMail.VerifySignature();
        ShowMessage('This email contains a valid digital signature.');
        // You can add the certificate to your certificate storage like this
        // oSignerCert.AddToStore(CERT_SYSTEM_STORE_CURRENT_USER,
        // 'addressbook');
        // Then you can use send the encrypted email back to this sender.
    Except
        On ep: Exception Do
        Begin
            ShowMessage('Verify signature Error: ' + ep.Message);
        End;
    End;


    // Parse email sender
    ShowMessage('From: ' + oMail.From.Address);

    // Parse email to recipients
    addrs := oMail.ToAddr;
    UBound := VarArrayHighBound(addrs, 1);
    For i := 0 To UBound Do
    Begin
        addr := IDispatch(VarArrayGet(addrs, i)) As IMailAddress;
        ShowMessage('To: ' + addr.Address);
    End;

    // Parse email cc recipients
    addrs := oMail.Cc;
    UBound := VarArrayHighBound(addrs, 1);
    For i := 0 To UBound Do
    Begin
        addr := IDispatch(VarArrayGet(addrs, i)) As IMailAddress;
        ShowMessage('Cc: ' + addr.Address);
    End;

    // Parse email subject
    ShowMessage('Subject: ' + oMail.Subject);

    // Parse email text body
    ShowMessage('Text body: ' + oMail.TextBody);

    // Parse email HTML body
    ShowMessage('HTML body: ' + oMail.HtmlBody);

    // Parse attachment
    atts := oMail.Attachments;
    UBound := VarArrayHighBound(atts, 1);
    For i := 0 To UBound Do
    Begin
        att := IDispatch(VarArrayGet(atts,i)) As IAttachment;
        ShowMessage(att.Name);
    End;

End;

Procedure TForm1.Button1Click(Sender: TObject);
Begin
    Try
        ParseEmail('c:\my folder\test.eml');
    Except
        On ep:Exception Do
        ShowMessage('Error: ' + ep.Message);
    End;

End;

End.

32bit/x64 ActiveX DLL

Seperate builds of run-time dll for 32 and x64 platform

File Platform
Installation Path\EAGetMailObj.dll 32 bit
Installation Path\x64\EAGetMailObj.dll 64 bit

Distribution

  • Standard EXE

    For VB6, C++, Delphi or other standard exe application, you can distribute EAGetMailObj.dll with your application to target machine without COM-registration and installer. To learn more detail, please have a look at Registration-free COM with Manifest File.

  • Script

    For ASP, VBScript, VBA, MS SQL Stored Procedure, you need to install EAGetMail on target machine by EAGetMail installer, both 32bit/x64 DLL are installed and registered.

Appendix

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