Suppose that you receive an email from someone claiming to be Alice, and the ema

Question

Suppose that you receive an email from someone claiming to be Alice, and the email included a digital certificate that contains M = ("Alice", Alice's public key) and [h(M)]_CA, where CA is a certificate authority. How do you verify the signature? Be precise. Why do you need to bother to verify the signature? Suppose that you trust the CA who signed the certificate. Then, after verifying the signature, you will assume that only Alice possesses the private key that corresponds to the public key contained in the certificate. Assuming that Alice's private key has not been compromised, why is this a valid assumption? Assuming that you trust the CA who signed the certificate, after verifying the signature, what do you know about the identity of the sender of the certificate?

Explanation / Answer

(a). We can verify the signature, by verifying that M = {S} Alice. Then verify the hash signature M and comparing the result to the value is obtained when Alice's public key is applied to S and verify that h(M) = {S} Alice

(b). Because the signature is the one that corroborates the authenticity of the message or the email that in this case sends alice.

(c). The CA is attesting to the fact that it gave the private key corresponding to Alice. That is, the CA creates a public and private key pair and put the key audience on Alice's certificate. The CA then signed the certificate (using her private key) and gave the private key to Alice. If you trust the CA, you believe that you actually gave Alice the private key, not any other person.

(d). Once the certificate is verified the public key can be known, as well as a lot of information about the   person or thing that holds this private key.

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