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With the help of these features, the following benefits are provided:
► From the moment the message is sent to the moment it is delivered to its final
destination, no one can see the contents of the message.
► The recipient can be certain that the message came from the person that he
or she thinks it came from.
► It is also certain that the message has not been tampered with or changed on
the way to delivery.
Encryption for message privacy
For message privacy, or confidentiality, S/MIME uses asymmetric keys
(public/private keys) to encrypt messages. This is essentially the same technique
as is employed in Notes and explained in the Notes PKI section.
To send an encrypted S/MIME message, it is necessary to obtain the recipient’s
public key and encrypt the message using this key. Since the only person who
has its associated private key is the recipient, the message can be sent safely
with the assured knowledge that only the recipient will be able to decrypt this
message. This technique is exactly like the one used in Notes and shown in
Figure 6-16 on page 227 and in Figure 6-26.
Figure 6-26 Electronic mail message encryption in S/MIME
This is a practical application of the hybrid solution that we covered in the
security fundamentals chapter. The numbered steps in Figure 6-26 are described
as follows:
1. Alice decides to send an encrypted S/MIME message to Bob. The messaging
client, seeing that the messages needs to be encrypted, generates a random
Chapter 6. Public key infrastructures 269