Joe, 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 Joe’s certificate? (Choose two.)
The CA’s public key
Joe’s private key
Ann’s public key
The CA’s private key
Joe’s public key
Ann’s private key
Joe wants to send a message to Ann. It’s important that this message not be altered. Joe will use the private
key to create a digital signature. The message is, in effect, signed with the private key. Joe 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 Joe. Ann will use a key provided by Joe—
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 Joe 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 Joe. If a third party (the CA) vouches for Joe and Ann trusts that third party,
Ann can assume that the message is authentic because the third party says so.