Page 245 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 14: Authentication

However, programming all the authorized users' MAC addresses into all the company's access Notes
points can be an arduous task for a large organization and can be time consuming - but for the
home technology enthusiast, or for small network installations, using a MAC filtering technique
can be a very effective method to prevent unauthorized access.
Media Access Control assigns a unique number to each IP network adapter called the MAC
address. A MAC address is 48 bits long. The MAC address is commonly written as a sequence of
12 hexadecimal digits as follows:
48-3F-0A-91-00-BC
MAC addresses are uniquely set by the network adapter manufacturer and are sometimes called
physical addresses. The first six hexadecimal digits of the address correspond to a manufacturer's
unique identifier, while the last six digits correspond to the device's serial number. MAC
addresses map to logical IP addresses through the Address Resolution Protocol (ARP).
Some Internet service providers track the MAC address of a home router for security purposes.
Many routers support a process called cloning that allows the MAC address to be simulated so
that it matches one the service provider is expecting. This allows households to change their
router (and their real MAC address) without having to notify the provider.

Self-Assessment

State whether the following statements are true or false:
8. All IEEE 802 network devices share a common 50-bit MAC address format.

9. Wireless networks are a helpful method for easily sharing network resources and
connections.
10. MAC addresses are uniquely set by the network adapter manufacturer.

14.4 Public-key Cryptography

Cryptography is the study of protecting information through the use of codes and ciphers.
Cryptography forms a fundamental part of message security.
At its simplest, a code is a process of methodically changing information to make it unreadable
without knowing how that information was changed. One of the earliest and simplest codes
(called a Caesar cipher) worked by taking the alphabet and shifting all the letters by a fixed
number. The sender and recipient would both know how many letters to shift and thus could use
this code to change information so that each would be able to understand, but no one else could
understand. This process of changing information into a code is encryption and the process of
changing code back is decryption. The original message is referred to as "plaintext." The changed
message is referred to as "ciphertext." The information that is used to change the plain text into
ciphertext is referred to as the key. The particular way in which a key changes information is
referred to as the algorithm.

Notes Plaintext (or cleartext) in this context should not be confused with plain text
when referring to the format of an e-mail message. In that context, plain text is used to
differentiate a message's format from HTML format or Rich Text Format (RTF). In the
context of message security, plaintext is used to differentiate from ciphertext to indicate
that the text is not encrypted.

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