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), and cσ =Enc(pkC, σ).Aldebaran sends this ciphertext along with their usual broadcast(pkC, cdest, cmsg). Chandra performs her usual steps, as well as decrypting to obtain σ =Dec(skC, cσ). She sends it along with her usual broadcast (pkB, c′msg) for Borealis. Lastly, Borealis, decrypts to obtain the message m. Borealis believes the message should have come from Aldebaran. He runs Verify(pk′A, m, σ) and is satisfied only if the signature accepts.
Question
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), and cσ =Enc(pkC, σ).Aldebaran sends this ciphertext along with their usual broadcast(pkC, cdest, cmsg). Chandra performs her usual steps, as well as decrypting to obtain σ =Dec(skC, cσ). She sends it along with her usual broadcast (pkB, c′msg) for Borealis. Lastly, Borealis, decrypts to obtain the message m. Borealis believes the message should have come from Aldebaran. He runs Verify(pk′A, m, σ) and is satisfied only if the signature accepts.
Solution
This method is secure. Here's why:
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Aldebaran signs the message with his private key. This ensures that the message is indeed from Aldebaran, as only he has access to his private key.
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The signature is then encrypted with Chandra's public key. This ensures that only Chandra can decrypt the signature, as she is the only one with the corresponding private key.
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Chandra decrypts the signature and sends it along with her usual broadcast. This ensures that the signature is not tampered with during transmission.
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Borealis decrypts the message and verifies the signature using Aldebaran's public key. This ensures that the message is indeed from Aldebaran and has not been tampered with during transmission.
Therefore, this method provides a secure authentication mechanism. It ensures that the message is from Aldebaran, that it has not been tampered with during transmission, and that only the intended recipient can read it.
However, it's important to note that this method does not hide Aldebaran's identity from eavesdroppers. Anyone who intercepts the message can see that it's from Aldebaran by checking the signature with his public key. If anonymity is a requirement, this method would not be suitable.
Similar Questions
The SSL protocol addresses the confidentiality and the integrity of a message through:Group of answer choicessymmetric encryptionmessage authentication codehash functiondigital signature certificates
(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.
(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).
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).
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
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