Dana has registered her public key Kp with the certificate authority CA, whose public key is Kca. She wishes to send a message m to Earl, who does not know Dana and does not recognize the authority of CA. Fortunately, Dana knows Earl's good friend Finn, who does recognize CA's authority. Furthermore, both Earl and Finn work at Gaggle and have registered their public keys (Ke and KF, respectively) with the company's certificate authority, the public key for Gaggle's certificate authority is KG (Note that both Earl and Finn have access to Gaggle certificates, but they have never exchanged their public keys with one another before.) Dana signs her message using her private key, and sends it to Finn. She asks Finn to forward it to Earl, which Finn does as follows: • Finn uses his private key to sign Dana's signed message, and sends the result to Earl.
• Finn also gets a copy of Dana's public-key certificate, and signs and sends that to Earl
• Finn signs a message that indicates what CA's public key is, and sends that to Earl. . Finally, Finn signs and sends to Earl a message stating his confidence in CA's jurisdiction over Dana's public key.
a. Express in the access-control logic the four items that Finn sends to Earl.
b. Identify the additional certificates, recognitions of authority, and any other trust assumptions that Earl requires in order to deduce that the message m truly came from Dana. You should express each of these items in the access control logic.
c. Give a formal proof that m can be deduced from your answers to parts (a) and (b).
d. In your opinion, which if any of the assumptions from part (b) are the most suspect? Explain your answer.