ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 85)

the next round. At the end of the last round, which does not require transformation

mechanism M, the data block is considered encrypted.

Once all the blocks for a given message are encrypted, they are reassembled in

order to create the encrypted message that can then be transmitted over the network.

The AES encryption procedure is illustrated in Figure 4.3.

Decryption is the opposite process of encryption as illustrated in Figure 4.4.

AES, which was used by the U.S. administration to replace DES, was also chosen

as the new encryption algorithm for the IEEE 802.11i standard to replace RC4.

Public-Key Cryptography

The public-key cryptography technique solves the main problem with symmetric

keys, which resides in the key transmission.

Two types of keys are used with public-key cryptography:

•

A private key for data decryption. This key must remain confidential.

•

A public key, which is placed at the disposal of all the users. This key is used

for data encryption.

There is a mathematical link between these two keys, so finding the value of one

of the two keys from the other one is very difficult.

The public key is sent over the network in plain text so it can be encrypted. The

recipient uses his private key for data decryption as soon as the encrypted data has

been received. This process is illustrated in Figure 4.5.

66 Security

Figure 4.3 AES encryption

Figure 4.4 AES decryption

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 85