Peter, a user, wants to send an encrypted email to Ann. Which of the following will Ann need to use to verify the validity’s of Peter’s certificate? (Select TWO).
A. The CA’s public key B. Peter’s private key C. Ann’s public key D. The CA’s private key E. Peter’s public key F. Ann’s private key
Answer: A,E
Explanation: Peter wants to send a message to Ann. It’s important that this message not be altered. Peter will use the private key to create a digital signature. The message is, in effect, signed with the private key. Peter then sends the message to Ann. Ann will use the public key attached to the message to validate the digital signature. If the values match, Ann knows the message is authentic and came from Peter. Ann will use a key provided by Peter—the public key—to decrypt the message. Most digital signature implementations also use a hash to verify that the message has not been altered, intentionally or accidently, in transit. Thus Ann would compare the signature area referred to as a message in the message with the calculated value digest (her private key in this case). If the values match, the message hasn’t been tampered with and the originator is verified as the person they claim to be. This process provides message integrity, nonrepudiation, and authentication. A certificate authority (CA) is an organization that is responsible for issuing, revoking, and distributing certificates. A certificate is nothing more than a mechanism that associates the public key with an individual. If Peter wants to send Ann an encrypted e-mail, there should be a mechanism to verify to Ann that the message received from Mike is really from Peter. If a third party (the CA) vouches for Peter and Ann trusts that third party, Ann can assume that the message is authentic because the third party says so.