In previous section, I introduced how to send email with embedded images. In this section, I will introduce how to sign email with digital certificate in Visual C++.
Sections:
Digital signature prevents email content is faked or changed in transport level. Encrypting email protects email content from exposure to inappropriate recipients. Both digital signature and email encrypting depend on digital certificate.
If you have an email digital signature certificate installed on your machine, you can find it in “Control Panel” -> “Internet Options” -> “Content” -> “Certificates” -> “Personal”.
Then you can use your email certificate to sign the email by the following code. If you don’t have a certificate for your email address, you MUST get a digital certificate for personal email protection from third-party certificate authorities such as www.verisign.com.
If you need a free certificate for your email address, you can go to http://www.comodo.com/home/email-security/free-email-certificate.php to apply for one year free email certificate.
Note
Remarks: All of samples in this section are based on first section: A simple Visual C++ 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.
The following example codes demonstrate how to sign email with digital certificate.
Note
To get the full sample projects, please refer to Samples section.
#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("email from Visual C++ with digital signature(S/MIME)");
// Set email body
oSmtp->BodyText = _T("this is a test email sent from Visual C++ with digital signature");
// 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;
}
_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;
}
You can use SignatureHashAlgorithm property to set MD5, SHA1, SHA256, SHA384 or SHA512 signature algorithm. SHA256 is recommended.
Next Section
At next section I will introduce how to encrypt email with digital certificate.
Appendix
Comments
If you have any comments or questions about above example codes, please click here to add your comments.