SixFile is a GUI application (currently only for Windows) that allows creation of an S/MIME protected file, complete with attachments, digital signature and digital envelope. Instead of sending the S/MIME file to an Email recipient over SMTP, SixFile writes it to a file. That file can be on a thumb drive, a CDROM, a shared file system, or a shared DropBox folder. The file is of type “.eml”, which is linked to your default E-mail client (if you double click on an .eml file it will pop into your E-mail client, which processes the S/MIME security). You can think of SixFIle as SMTP-Less S/MIME – it never goes through Email servers.
The .eml file is digitally signed, using your own private key, and your cert is included in the S/MIME message so any recipient can verify the digital signature. It is also typically encrypted, using the recipient’s public key (from their certificate, which is kept in a Personal Address Book, or a shared LDAP address book. Each entry has a name, email address and S/MIME certificate.
The received files in a DropBox or other cloud-based storage provider folder would display as below:
If I double click on the last one, it will pop into your Outlook client as below:
It looks just like it arrived via SMTP but came via DropBox instead. It can handle files of any type and size (unlike Email attachments which are limited to about 5-10 MB).
Shortly we will add the ability to send the S/MIME message to an FTP server via FTP/FTPS or an SSHD server via SFTP.
However the S/MIME message is sent, it is true end-to-end privacy, with original sender to final recipient authentication, which is otherwise difficult to accomplish with file sharing or file transfer. This is a new and innovative use of the IETF S/MIME security protocol.