How to execute local native compiled code in windows and use the output as input to a webmail application?

Question

I hope my question is not redundant. I have a small program (Windows Visual C++ native app) which can take a file and encrypt it using AES. It also can take text as input and also generate an encrypted version of the text.

What I want to achieve is to make this utility to interact with web mail applications, such as Microsoft Outlook or Google Gmail, In a way that is as transparent as possible for the user.

For example: User creates an email message, types his text, and then with a button, the small native program is called and the text is encrypted and it replaces the text that the user has entered in the email form. This text is sent, and the receiver can decrypt it from his web mail page (also pressing a button) and see the plain text on his screen.

For sake of simplicity I leave out the discussion about key management, etc.

I also want to apply the same scenario to email attachments.

I know that Greasemonkey can be used to change the appearance of a web page, and have been also looking at XPCOM objects in order to call local code, but I am not sure yet if this is the best approach. I would like to hear of alternatives if there are any.

Thanks in advance for your help!

Answer 1

Responding to my own question for anyone who finds it in the future. I got a couple useful comments from Brock Adams and did a bit more research. After looking at some options, looks like I will use XUL to build a Firefox Add-on. As for the execution of native code, js-ctypes looks like the best option for me since I already have my native code in a dll.