Applications and the Future - Codes: The Guide to Secrecy from Ancient to Modern Times - page 331

hard drive. 9.1 This might be done via temporary storage in a buffer for later
analysis. Employers might want to monitor any number of employee activities
such as who visits the employee's site; what an employee downloads, including
streamingaudio and video; contents of incomingand outgoinge-mail messages;
which sites the employee visits; and the contents of what they view at a given
site. The amount of tra L c scanned by a given packet sniffer will depend on the
location of the computer in the network. If it is located in a relatively secluded
area of the network, then the sniffer will be able to scan only a tiny portion
of traLc over the network. However, if it is the principal domain server, for
instance, the packet sniffer will be able to scan virtually all of the traLc.
The above beingsaid, Mallory still likes packet sniffers, since if successful,
he can use them to seize passwords from data packets traversingthe network
and wreak havoc as described above. One method of thwartingMallory is to
encipher the headers of packets usingSSL in browser-based traLc (see Section
5.7).
Ethernet and Promiscuous Mode
Ethernet (as specified in IEEE 9.2 802.3), is the most commonly employed
Local Area Network (LAN). Ethernet evolved from a framework called Alohanet ,
named for the Palo Alto Research Center Aloha Network , which was developed
into Ethernet by XEROX, then further expanded later by DEC, Intel, and
XEROX. There exist Ethernet configurations that provide transmission speeds
up to 10 billion bits per second, called Ten-Gigabit Ethernet , which is specified
in IEEE 802.3a. The future of all interconnections of LANs, WANs, and MANs
is generally predicted to be via the Ten-Gigabit Ethernet.
Now that we know the basics of Ethernet, we describe the use of packet
sniffers in this context. Ethernet was designed to filter out all data traLc not
belonging to it. When a packet sniffer is installed in Ethernet hardware, that
filter is turned off and the hardware goes into promiscuous mode. Thus, if Alice
9.1 Although we gave a basic definition of a hard drive in Footnote 8.22 on page 324, we will
expand it here to get a better idea of how they function. A hard diskis essentially a collection
of stacked disks, each storing data electromagnetically recorded in concentric circles, called
tracks .Two heads , one located on each side of a disk, read or write the information on these
tracks as the disk spins. The spin speed is anywhere from 4500 to 7200 rpms. Think of the
comparison with a phonograph record and its player having a phonograph arm (“head”), to
“read” the music.
9.2 IEEE, pronounced I-Triple E , is the Institute of Electrical and Electronics Engineers
Incorporated. The AIEE, American Institute of Electrical Engineers, which was founded in
1884, merged with the IRE, Institute of Radio Engineers, in 1963 to form IEEE. The primary
function of IEEE, for our interest, is the development of standards for communications security,
the most famous of which are the IEEE 802 standards for LANs and WANs. A LAN is a
collection of computers and their attendant mechanisms sharing a common communications
channel or wireless linkage, and (usually), a shared server. The common server has applications
and data storage, which may be accessed by the LAN users who may vary in number from
a couple to several thousand. A WAN is a Wide Area Network , which differs from a LAN
in that it is a geographically more dispersed network, which usually includes shared user
networks. In size between a LAN and a WAN is a MAN or Metropolitan Area Network ,
typically meaning the interconnection of networks in a city into a single large network. A
MAN, of course, provides a more e6cient connection to a WAN. For more information on
IEEE and its standards, visit http://www.ieee.org/portal/index.jsp .