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An integration of PGP and MIME

Internet text mail has been developing to satisfy various user requests, such as transporting non-textual objects and privacy enhancements. While MIME redefined the mail body format to support non-textual objects and multipart structure, PGP provides encryption and digital signature features for text mail. MIME however does not provide privacy services whereas non-textual objects cannot be exchanged with PGP. It is of recent interest to integrate PGP and MIME so that users can make use of these two services at the same time. This paper describes an integration of PGP and MIME. Our scheme embeds PGP objects into MIME and maintains backward compatibility with PGP. It is possible to encrypt, sign, and sign-then-encrypt non-textual objects, single-parts in a multi-part, an entire multipart, etc. We also explain our viewing and composing mechanisms that allow users to handle PGP/MIME messages intuitively without format restrictions.