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ivan  
#1 Posted : Monday, May 2, 2011 12:24:59 AM(UTC)
ivan

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Delphi 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

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. 

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