In this chapter, you learned how GPG can protect e-mail confidentiality. We created a threat model for our system and showed how this analysis can help us understand the capabilities and limitations of our design. At the end, we successfully built a BBB GPG co-processor that uses a TPM to help protect the GPG keys at rest and got more practice combining a microcontroller with an embedded Linux platform.

In the next chapter, we will investigate another major privacy enhancing technology that is used to protect real-time chat. You'll learn about the unique cryptographic properties of Off-the-Record (OTR) and how to use OTR over an Internet Relay Chat gateway that is hosted by your BBB.