Abstract

Much electronic mail is sent unencrypted, making it vulnerable to passive eavesdropping. We propose to protect email privacy by building encryption functionality into ESMTP mailers. Our solution, ssmail, provides fast, simple encryption for sendmail that does not require user intervention or reliance on public key infrastructure. We added a small number of steps to an ESMTP session, thereby allowing a client and server to create a secret, one-time session key used to encrypt the mail transfer session. ssmail relies on caching to reduce key generation overhead. The overhead imposed by our encryption scheme is minimal, allowing even busy mail servers to support privacy. We placed our encryption mechanism within the mail transfer agent itself, allowing people to use privacy protection software without having to know how to run an encryption program explicitly. Furthermore, we are able to encrypt the email transmission session, protecting such information as sender and recipient identities. The speed and simplicity of ssmail make it a very useful addition to widely deployed ESMTP mailers. Our solution can also be adopted easily by other mailers, and can be extended to use other encryption algorithms.

Citations