How do digital certificates work in e-mail correspondence?
Suppose Sender wants to send a signed data/message to the recipient. He creates a message digest (which serves as a “digital fingerprint”) by using a hash function on the message. Sender then encrypts the data/message digest with his own private key. This encrypted message digest is called a Digital Signature and is attached to sender’s original message, resulting in a signed data/message. The sender sends his signed data/message to the recipient. When the recipient receives the signed data/message, he detaches sender’s digital signature from the data/message and decrypts the signature with the sender’s public key, thus revealing the message digest. The data/message part will have to be re-hashed by the recipient to get the message digest. The recipient then compares this result to the message digest he receives from the sender. If they are exactly equal, the recipient can be confident that the message has come from the sender and has not changed since he signed it. If the message dige
Figure 3: How Alice creates a Signature Suppose Alice wants to send a signed message to Bob. She creates a message digest (which serves as a “digital fingerprint”) by using a hash function on the message. Alice then encrypts the message digest with her own private key. This encrypted message digest is called a Digital Signature and is attached to Alice’s original message, resulting in a signed message. Alice sends her signed message to Bob (Figure 3). When Bob receives the message (Figure 4), he detaches Alice’s digital signature from the message and decrypts the signature with Alice’s public key, thus revealing the message digest. The message part will have to be re-hashed by Bob to get the message digest. Bob then compares this result to the message digest from Alice. If they are exactly equal, Bob can be confident that the message really is from Alice and has not changed since she signed it. If the message digests are not equal, the message may not have come from Alice, was altered
