Managing Digitally Signed Messages

Aspose.Email implements the complete S/MIME email object algorithm. This gives the API complete power to add digital signatures to email messages, preserve them while converting messages between formats, remove them, etc.

Attach a Signature to an Email

The SecureEmailManager.attachSignature method allows you to attach digital signatures to email messages. After attaching the signature, verify the results through properties like IsSigned, MessageClass, and attachment details.

You can provide a MailMessage or MapiMessage, a private certificate, and signature options to customize the signature attachment process with the SignatureOptions class which enables users to specify various options for the signature attachment, including detached or non-detached signatures.

The following code sample will show you how to load a message from a file, attach a detached and non-detached digital signature using a private certificate, and then check if the signatures were attached successfully.

String fileName = "message.msg";
String privateCertFile = "certFile.pfx";
X509Certificate2 privateCert = new X509Certificate2(privateCertFile, "password");

MapiMessage msg = MapiMessage.load(fileName);

SignatureOptions opt = new SignatureOptions();
opt.setDetached(true);
MapiMessage signedDetached = new SecureEmailManager().attachSignature(msg, privateCert, opt);

if (signedDetached.isSigned()) {
    System.out.println("Detached Signature Attached Successfully.");
}

opt.setDetached(false);
MapiMessage signedNonDetached = new SecureEmailManager().attachSignature(msg, privateCert, opt);

if (signedNonDetached.isSigned()) {
    System.out.println("Non-Detached Signature Attached Successfully.");
}

Preserving Signature when Converting from EML to MSG

Aspose.Email preserves the digital signature when converting from EML to MSG. The following code snippet shows you how to convert from EML to MSG.

// For complete examples and data files, please go to https://github.com/aspose-email/Aspose.Email-for-Java
// The path to the File directory.
String dataDir = "outlook/";

// Load mail message
MailMessage message = MailMessage.load(dataDir + "Message.eml", new EmlLoadOptions());
// Save as MSG
message.save(dataDir + "ConvertEMLToMSG_out.msg", SaveOptions.getDefaultMsgUnicode());

Remove Signature from an Outlook Message File

If you’re facing the necessity to remove the signature from a message in a MAPI format, for example for compatibility purposes, Aspose.Email offers the MapiMessage.removeSignature method and the MapiMessage.isSigned property.

The following code snippet shows how to load a MAPI message from a file, check if it is digitally signed, and if so, create a new message without the digital signature:

MapiMessage msg = MapiMessage.load(fileName);

if (msg.isSigned()) {
    MapiMessage unsignedMsg = msg.removeSignature();
}

Converting S/MIME Messages from MSG to EML

Aspose.Email preserves the digital signature when converting from MSG to EML as shown in the following code snippet.

// For complete examples and data files, please go to https://github.com/aspose-email/Aspose.Email-for-Java
// The path to the File directory.
String dataDir = "outlook/";

MailMessage msg = MailMessage.load(dataDir + "message.eml");
MapiMessage mapi = MapiMessage.fromMailMessage(msg, new MapiConversionOptions(OutlookMessageFormat.Unicode));
// Save File to disk
mapi.save(dataDir + "ConvertMIMEMessagesFromMSGToEML_out.msg");

Decrypt an MSG File with Certificate

If you have encrypted MAPI messages and need to decrypt them using the private key stored in a certificate, the following features of Aspose.Email can be useful:

• MapiMessage.isEncrypted - Gets a value indicating whether the message is encrypted.
• MapiMessage.decrypt() - Decrypts this message (method searches the current user and computer My stores for the appropriate certificate and private key).
• MapiMessage.decrypt(X509Certificate2 certificate) - Decrypts this message with certificate.

The following code snippet shows how to work with encrypted MAPI messages:

X509Certificate2 privateCert = new X509Certificate2("privateCertFile", "password");
MapiMessage msg = MapiMessage.load("encrypted.msg");

if (msg.isEncrypted()) {
    MapiMessage decryptedMsg = msg.decrypt(privateCert);
    //MapiMessage decryptedMsg = msg.decrypt(/*byte[]*/rawPrivateCert, "password");
}