Managing Digital Signatures with Aspose.Email

The library provides the LoadOptions class, an abstract base class that allows the user to specify additional options when loading a MailMessage from a particular format. The signature preserving option is set by default.

Convert EML to MSG While Preserving Signatures

The code sample below demonstrates how to load a message, convert it to MSG format and save as MSG (the signature is preserved by default):

import aspose.email as ae

# Load mail message
loadOptions = ae.EmlLoadOptions()
message = ae.MailMessage.load("Message.eml", loadOptions)
# Save as MSG
message.save("ConvertEMLToMSG_out.msg", ae.SaveOptions.default_msg_unicode)

Convert S/MIME Messages from MSG to EML

Aspose.Email allows you to convert from MSG to EML preserving a digital signature as shown in the following code snippet.

import aspose.email as ae

# Load mail message
loadOptions = ae.EmlLoadOptions()
smime_eml = ae.MailMessage.load("smime.eml", loadOptions)

conversion_options = ae.mapi.MapiConversionOptions(ae.mapi.OutlookMessageFormat.UNICODE)
msg = ae.mapi.MapiMessage.from_mail_message(smime_eml, conversion_options)
# Save File to disk
msg.save("ConvertMIMEMessagesFromMSGToEML_out.msg")

Check Signatures of Secure Emails

The following features are available to check the signature of MapiMessage objects:

• the SecureEmailManager class for checking the signature of secure emails;
• the SmimeResult class that stores the result of the check in its is_success property;
• the check_signature(msg) and check_signature(msg, certificate) methods of the SecureEmailManager class.

In Aspose.Email for Python via .NET a certificate is passed as a byte sequence: read the certificate file in binary mode and pass the resulting bytes object.

Check the signature of a message without providing a certificate:

import aspose.email as ae
from aspose.email.mapi import MapiMessage

msg = MapiMessage.load(data_dir + "signed.msg")

result = ae.SecureEmailManager().check_signature(msg)
print("Signature is valid: " + str(result.is_success))

Check the signature of an encrypted message by providing the certificate used for decryption:

import aspose.email as ae
from aspose.email.mapi import MapiMessage

with open(data_dir + "cert.pfx", "rb") as f:
    certificate = f.read()

msg = MapiMessage.load(data_dir + "signed_and_encrypted.msg")

result = ae.SecureEmailManager().check_signature(msg, certificate)
print("Signature is valid: " + str(result.is_success))

Remove Signatures from MapiMessages

For better compatibility, the remove_signature method and the is_signed property of the MapiMessage class are used to remove a digital signature from a message:

from aspose.email.mapi import MapiMessage

msg = MapiMessage.load(data_dir + "signed.msg")

if msg.is_signed:
    unsigned_msg = msg.remove_signature()
    unsigned_msg.save(data_dir + "unsigned.msg")

Decrypt MapiMessages with Certificates

If you have encrypted MAPI messages and need to decrypt them with the private key stored in a certificate, the following members of the MapiMessage class are useful:

• is_encrypted – gets a value indicating whether the message is encrypted.
• decrypt() – decrypts the message. The method searches the current user and computer My stores for the appropriate certificate and private key.
• decrypt(certificate) – decrypts the message with the given certificate. The certificate is passed as a bytes object and must contain the private key.

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

from aspose.email.mapi import MapiMessage

with open(data_dir + "private_cert.pfx", "rb") as f:
    private_cert = f.read()

msg = MapiMessage.load(data_dir + "encrypted.msg")

if msg.is_encrypted:
    decrypted_msg = msg.decrypt(private_cert)
    print(decrypted_msg.subject)