The consortium are interested in implementing signatures into the crypto-system. The goal is to provide an authentication mechanism which allows a recipient to see from whom the message originated. The consortium leader considers several options for how to implement this mechanism. State whether or not each option is secure, and provide a justification. Suppose Aldebaran wishes to send a message to Borealis, and Aldebaran possesses a signing keypair (sk′A, pk′A). (Hint: think about what eavesdroppers can learn about the identities of senders) Aldebaran computes σ = Sign(sk′A, m), andcσ = Enc(pkC, Enc(pkB, σ)). Aldebaran sends cσ along with their usual broadcast,(pkC, cdest, cmsg). Chandra performs her usual steps, as well as decrypting to obtain c′σ = Dec(skC, cσ). She sends it along with her usual broadcast, (pkB, c′msg) for Borealis. Lastly, Borealis, who will receives the message m, now also obtains σ =Dec(skB, c′σ). Borealis believes the message should have come from Aldebaran. He runs Verify(pk′A, m, σ) and is satisfied only if the signature accepts.

The SSL protocol addresses the confidentiality and the integrity of a message through:Group of answer choicessymmetric encryptionmessage authentication codehash functiondigital signature certificates

(15 marks) One of the approaches below is ”secure”. For each approach, state Secure or Insecure, and explain why that approach does or does not achieve the two desired notions of confidentiality described above. (a) Aldebaran computes c = Enc(pkB , m) and broadcasts (pkB , c). Borealis observes the broadcast containing their public key and obtains the message as m = Dec(skB , c).

(Encrypt-then-Sign-then-Encrypt) Recall that the original crypto-system, Aldebaran computes the double encryption cmsg = Enc(pkC, c′ msg) where c ′ msg = Enc(pkB, m). In this approach, Aldebaran computes σ = Sign(sk′ A, c′ msg), and then encrypts cσ = Enc(pkC, σ). Aldebaran sends cσ along with their usual broadcast. Chandra performs her usual steps, as well as decrypting to obtain σ = Dec(skC, cσ). She broadcasts σ along with her usual broadcast (pkB, c′ msg) for Borealis. Lastly, Borealis, believes the message should have come from Aldebaran. He runs Verify(pk′ A, c′ msg, σ), and decrypts c ′ msg to obtain m only if the signature accepts.

Which of the following is the most reliable sender authentication method?Group of answer choicesDigital signaturesAsymmetric cryptographyDigital certificatesMessage authentication code

ohn recently received an email message from Bill. What cryptographic goal would need to be met to convince John that Bill was actually the sender of the message?Group of answer choicesAvailabilityIntegrityConfidentialityNonrepudiation