Visual C++ - Encrypt Email - S/MIME

The following c++ example codes demonstrate how to encrypt email to S/MIME format with digital signature.

Email Encryption

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.

Installation

EASendMail is a SMTP component which supports all operations of SMTP/ESMTP protocols (RFC 821, RFC 822, RFC 2554). Before you can use the following example codes, you should download the EASendMail Installer and install it on your machine at first.

Add Reference

To use EASendMail SMTP ActiveX Object in your C++ project, the first step is “Add header files of EASendMail to your project”. Please go to C:\Program Files\EASendMail\Samples_VC\simple.vcNative or C:\Program Files (x86)\EASendMail\Samples_VC\simple.vcNative folder, find easendmailobj.tlh and easendmailobj.tli, and then copy these files to your project folder.

add reference in Visual C++

C++ - Encrypt Email - S/MIME - Example

The following example codes demonstrate encrypting email message with digital signature - S/MIME. In order to run it correctly, please change SMTP server, user, password, sender, recipient value to yours.

Note

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

#include "stdafx.h"

#include "easendmailobj.tlh"
using namespace EASendMailObjLib;

int _tmain(int argc, _TCHAR* argv[])
{
    ::CoInitialize( NULL );

    IMailPtr oSmtp = NULL;
    oSmtp.CreateInstance( "EASendMailObj.Mail");
    oSmtp->LicenseCode = _T("TryIt");

    // Set your sender email address
    oSmtp->FromAddr = _T("test@emailarchitect.net");

    // Add recipient email address
    oSmtp->AddRecipientEx( _T("support@emailarchitect.net"), 0 );

    // Set email subject
    oSmtp->Subject = _T("Encrypted email from Visual C++ (S/MIME)");

    // Set email body
    oSmtp->BodyText = _T("this is a test encrypted email sent from Visual C++");

    // Your SMTP server address
    oSmtp->ServerAddr = _T("smtp.emailarchitect.net");

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

    // If your smtp server requires SSL connection, please add this line
    // oSmtp->SSL_init();

    //add signer digital signature
    if( oSmtp->SignerCert->FindSubject(_T("test@emailarchitect.net"),
        CERT_SYSTEM_STORE_CURRENT_USER , _T("my")) == VARIANT_FALSE )
    {
        _tprintf(_T("Error with signer certificate; %s\r\n"),
            (const TCHAR*)oSmtp->SignerCert->GetLastError());
        return 0;
    }

    if( oSmtp->SignerCert->HasPrivateKey == VARIANT_FALSE )
    {
        _tprintf(_T("certificate does not have a private key, it can not sign email.\r\n" ));
        return 0;
    }

    // Find the encrypting certificate for every recipients
    ICertificatePtr oCert = NULL;
    oCert.CreateInstance("EASendMailObj.Certificate");
    if( oCert->FindSubject(_T("support@emailarchitect.net"),
            CERT_SYSTEM_STORE_CURRENT_USER, _T("AddressBook")) == VARIANT_FALSE )
    {
        if(oCert->FindSubject(_T("support@emailarchitect.net"),
                CERT_SYSTEM_STORE_CURRENT_USER, _T("my")) == VARIANT_FALSE )
        {
            _tprintf( _T("Encrypting certificate not found; %s\r\n"),
                    (const TCHAR*)oCert->GetLastError());
            oCert.Release();
            return 0;
        }
    }

    // Add encrypting certificate
    oSmtp->RecipientsCerts->Add( oCert );
    oCert.Release();

    _tprintf(_T("Start to send email ...\r\n" ));

    if( oSmtp->SendMail() == 0 )
    {
        _tprintf( _T("email was sent successfully!\r\n"));
    }
    else
    {
        _tprintf( _T("failed to send email with the following error: %s\r\n"),
            (const TCHAR*)oSmtp->GetLastErrDescription());
    }

    if( oSmtp != NULL )
        oSmtp.Release();

    return 0;
}

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.

32bit/x64 ActiveX DLL

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

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

Distribution

  • Standard EXE

    For VB6, C++, Delphi or other standard exe application, you can distribute EASendMailObj.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 EASendMail on target machine by EASendMail installer, both 32bit/x64 DLL are installed and registered.

Appendix

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