Page 253 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 14: Authentication

z z Message is received. Notes
z z Encrypted message and encrypted session key are retrieved from the message.
z z Recipient's private key is retrieved.
z z Session key is decrypted with the recipient's private key.
z z Message is decrypted with the decrypted session key.
z z Digital signature containing encrypted hash value is retrieved from the message.

z z Hash value of the message is calculated.
z z Sender's public key is retrieved.
z z Encrypted hash value is decrypted with the sender's public key.
z z Decrypted hash value is compared against the hash value produced on receipt.

z z If the values match, the message is valid.
z z Unencrypted message is returned to the recipient.
The sequence shows how public key cryptography makes digital signatures and message
encryption possible.
Note how the public key or the private key of one party is required by the other party based on
the specific operation. For example, the sender must have his or her private key to digitally sign
e-mail, but must have the recipient's public key to send encrypted e-mail. Because this can be
confusing, a chart showing which keys are needed by which parties for which operation is shown
in the following figure 14.18.

Figure 14.18: Requirement of Keys to Parties

Source: http://technet.microsoft.com/en-us/library/aa998077(v=exchg.65).aspx
The next element to understand is digital certificates. Digital certificates make using digital
signatures and encryption possible by distributing key pairs.

Self-Assessment

Fill in the blanks:
10. …………………........ is the study of protecting information through the use of codes and
ciphers.
11. The reciprocal nature of the relationship of the key pair makes this unique identification
possible through …………………........ key cryptography.
12. Using a …………………........ key to establish identity shows that the full encryption and
decryption operation was accomplished successfully.

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